BREEDING PERFORMANCE OF BLACK-LEGGED KITTIWAKES ON GREAT ISLAND, NEWFOUNDLAND, DURING PERIODS OF REDUCED FOOD AVAILABILITY
rlHEIDI REGEHR
A thesis submitted to the School of Graduate Studies in partial fulfillmentof the
requirements for the degree of Master of Science
Department of Biology Memorial University of Newfoundland
1994
St.John's Newfoundland
1+1
NalionalU braryole.""d.
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ASS'l'RAC'l'
The breedingsuccessofBlac k -l e g ge dKit t iwak e~ (Ri s sa
~) was inv e s ti g a t e d on Great lelan d , Witle s s ua v, Newfoundland, in 1992 and 1993, following two yea rs of breedingfailure. Eggproducti onwas low in bothyears. High egg mortalities (90% and 89%) and highchickmortality in 1992 (93 %), but not in 1993 (32 %) , resultedin a breeding succes s of1% in 1992 and 7%in 1993. Timing of breedingwasla te r th a n in previousyears and clutchesand eggs were smal ler . Failure was extensive throughout the col ony. The degree of failurevaried consistentlyamong regionsbetweenyee ra which was probably related to cliffstructureand theref ore to nest predation. Comparison "f egg shape indices among years suggested that a higher proportion of olderin di v i d u als were breeding in years of poor productivity. This isco n si s t e nt with the hypothesis that older breeders are more abl e and wil lingto expend effort and incur cost.
Egg predation, primarily by Great Black-backed Gulls
(~marinus), accounted formo s t egg mortality. Results suggest that egg predation in both years and poor chick survival in 1992 were related to food shortage. Capelin (Mallotus~) arrivedinshore for spawning up to1month later than normal, which, in conjunctionwi t h a lack of fish offal,wa s associated with food shortagein kittiwakesand in
i i
oth e r gull s. Ki t tiwa ke incubationandchick -rearing shifts we r e shorter and surv ival time of chicks wa s longer af t er capelin arri valthan be f o r ein 1992, indicating increasedfood ava i l ability. Observationsand growth measurements indicated that chicks ha t.c hing be fore capelin arrival were starving.
Th e ef fe c t of hatchdateonchicksurvivalwas lesspr on o u nc e d in 1993 than in 1992. Unat tended eggs and chicks were uncommo n and ad u l t s endured long nest shifts, probably in re spo n s eto highpr e d a t i o nri sk . Incubation and chick-rearing shifts we r e sho rter and feeding rateswere greater in 1993 than in 1992, sugges t i n ggreaterfoodavailabi lity in 1993.
The seasona l migration of cape Li n into inshore wa t e r s in Wi t l ess Bay provides an important re s o u r ce to kittiwa kes, affecting their timebudgetsandsurvival of their chicks.
iii
FOR MY' FATHER
iv
ACKNOWLEDGEMENTS
I am very grateful to Bill Montevecchi for making this study possible. I thank him for his help, comments, and advice throughout this study, and for always, w.lt.hout;
ex c e p t i o n , finding time for help and discussion, and for financial support received through hisgrants. I thank my co- supervisor, John Chardine for his interest and discussion throughou t the study, and for helpful comments on the thesis.
I am also grateful tomyothercommitteemembers, Ransom Myers andAnne Story, for discussion and for reviews of thethee Le.
Robert Barrett and Laur'e-L Duquette provided constructive criticism whichhe l pe d to improve thiswo r k . Michael Rodway help e d inmo r e wa y s than I can recount. Mostly I thankhim for invaluableassistance in the field, for ideas, discussion, and forhe l pful comments on the thesis. Dave Schneider shared his et at.Lat Ica L wisdomforwh i c h I am very grateful. Merrill Francis ,WayneLidste r, Ja n ne t Russell, and PierreRyanhelp e d inth e move to the field ;their as s i s t a nc e in carrying heavy boxes up the hillwa s greatlyappreciated. Many than ks to Donna Butlerwho wa s alwayson handfor questions, help, and meeeaqee,andto Pie rreRyanfor providingsometransportation to the is l a ndan dfo r sha ringhis drafting materials. Thanks to Mu r r a y Colbo for help with funding, administration and other as pec t s of my graduate progra m. I would also li ke to
tha nk Lyndo n Cassel l , Peter Earle , Roy Ficke n, Gail Kenny.
Shirl e y Kenny , and Chr is Verson for technical and administrat i v e help. All·....ereveryhel p fu lan dcon tr ibut e dto maki ng this study enjoyable. The research cabi n on Grea t Island was used with permi s sion from the Canadian Wildl He Se rvice. Pers ona l fi nancialsupport was received fr o mNSERC lof Cana d a). The Re d d i c k family of Bau li ne pr ov i d ed tr a n s p o r ta t i on totheLaLand and radio contact. Ma ny tha n k s to Martin Rege hr for his wonde r ful e·mail comp a n ions hip . Las tly, with all my heart, I thankmy fathe r, Jac o b Reg ehr, for hi s limitle ss enc oura g e me n t of my dreams. With o ut him, muc h wo u l d not be.
vi
TABr.EOFCONTENTS
ABSTRACT DEDICATION i\CKNOWLEDGEMENTS TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF APPENDICES
CHAPTER 1INTRODUCTION 1 . 1.REFERENCES
CHAPT E R 2BREEDING SUCCESS OFBLACK-LEGGEDKITTIWAKES ON GREAT ISLAND IN 1992 AND 1993 2•1.ABSTRACT •
i i iv
vii xii
xvii
2.2. INTRODUCTION 11
2.3.METHODS 20
2.3.1.Study site and field schedule ?O 2.3.2.Reproductive p-=:rformance in the
study plots . . . 23
2.3.2 .1. Timing of breeding . 26
2.3.2.2. Analysis of disturbance effects 28 2.3.2.3. Comparisonof reproductive success
amongyears . . 29
2.3.3.Brood counts on Great Island during
the late chick stage 30
2.3.4.Statistics 33
vii
2.4. RESULTS ]5 2.4.1. Effectof re s e a r c he r disturbanceon
reproductive success in the study plots 35 2.4. 2. Kit t i wa k e breedingperformance in the
studypl o ts in1992and 199], and in
comparisonto previousye a r s ]7
2.4.2.1 . Breeding performa nce ]7
2.4 .2.2.Clutchsize 40
2.4.2.3.Egg size and shape
2.4.2 .4 .Changes in egg volume with laydate '17
2.4.2 .5.Timing of breeding . '19
2.4 .2.6 .Association be t we e n reproductive
me a sure samo ng years 52
2.4.3. Islandproductivityin19 92 and199] 52 2.4.4. Overall island pr od u c t ivi ty of1992and
19 93 in comp arison to estimated
productivity in1969and197 0 61
2.4.5 . Isla ndproductivityincomparisonto pr o du c t i vityinthest u d y plots 61
2.5.DISCUSSION 63
2.5. 1. Effect ofres e a r c h e r disturbance 63 2.5.2. ~reedingfailureof ki t t i wak e s in
wit l ess Bay 65
2.5.2.1.Wea the r , climat eandoce enoqre p htc
co nd i tion s . 68
2.5 . 2 . 2 .As s o ciatio ns bet wee n repro du c t i ve
measuresamong years 7 ]
2. 5.2 . 3.Eggshap e 78
2. 5 . 2.4.Re l ation s h ip betwee negg volume and
la yd ate . . 61
viii
2.5.3. Productivity acrossGreat Island 82
2.6. REFERENCES 85
CHAPTER3CAUSESOFBREEDING FA'I LUREOFBLACK- L EGGED KITTIWAKESONGREAT ISLAND,NEWFOUNDLAND,
IN 19 9 2 AND1993 96
3.1.A..,STRACT . 96
3.2. INTRODUCTION 98
3.3.METHODS 103
3.3. 1.Stud y site 10 3
3.3.2. Breed ing pe r f o r ma n c e 103
3.3.3 . Egg fates . . . . 104
3.3.3. 1Egg predation 104
3.3.3.2. Roleof kit tiwa ke eggs in Great
Black-backGullchickdiet . 105
3.3 .4. Fate of chicks . 106
3.3.5. Relationshipbetween timi ng of breeding and re p r o d u c ti v e success . . . 107 3.3.6. Foo davaila bi lity: timing of inshore
capelin arrival, incubationshifts, chick feeding, di et , and grow t h . lOB 3.3. 6.1.Timingof ca pelioinre j.at ion to
reproductivesucces s 10 8
3. 3.6.:2. Incubation shifts 109
3.3.6.3 .Ch ick feeding . . 111
3.3.6.4.Chick-r e a ring sh if ts 112
3.3.6.5. Diet . . . . 114
3. 3. 6. 6 .Chi c kgrowt h 114
3.3 .7 . Stat ist ics . . 115
ix
3 .4.RESULTS 116 3.4.1. Egg mortality
3.4.1.1. Fate of eggs 116
3.4.1 .2. Egg predation 116
3.4.1.3.Roleof kitt iwakeeggsinth e diet of Gr e a t Black-backedGu ll chicks 123
3.4 .2.Chick survival 12/j
3.4.3 . Relationship between timing of breeding
and reproductive success 12 6
3.4 .3 .1. Influence oflay d ate on hatching 126 3.4.3.2 . Influenceof hatchdateon the fate of
ch i c k s 13U
3.4.4. Fo od availabili t y . . . 133
3.4.4 .1.Timingof in s ho r e capelinarr i v a l in relation tokittiwakechick surv i v al 133
3.4.4.2 . Incubation shifts . 135
3.4.4.3.Chick~rearingshifts 13 9
3. 4.4 4. Chickfeeding rates 1'12
3. 4 . 4 .5 .Chic kdi e t 1'1.2
3.4.4 6.Chick growth 1'l4
3.5. DISCUSSION . 1'16
3.5.1. Egg mortali ty 146
3.5.1.1. Egg predators 14'1
3.5.1.2. Herring Gullsas a factor in kittiwake
bre e d i n g per f ormance 149
3.5.1.3.Factors involved in the intensityof.
predation . 15 1
3.5.1.4. Specialists 155
3.5.1.5. Timing of egg predation 156
3.5.2.Chicksurviva l . 158
3.5 .3. Timing of breeding inrela t i o nto
breeding success . . . 15 9
3. 5.4. Incubationand chfck- rearing shifts 163
3.5.5. Adul t nest attendance 168
3.5.6 . Chickfe e d i n g andgr owt h 172
3.6.REFERENCES 177
CHAPTER 4 CONCLUSIONS 18 5
4.1.REFERENCES . 190
xi
L'ISTOF TABL ES
Table 2.1 Comparison of the bree:ding performance of Black-leggedKittiwakesin observation and distu rbedplots on Great onGreat
Is lan d, Ne wfoun d l a nd , in1992 and1993 36 Ta ble2. 2 Summary of reproductive success of
Black-leggedKitti wakeson Great Isla n d , Ne wf oun d l an d, for 7study plots, in 1992 38 Tabl e 2. 3 Summaryof reproductive success of
Black-legged Ki t t iw a k e s on Great Is l an d , Ne wf o un d l a nd , for 8 study plots, in1993 39 Ta bl e 2.4 Comparison of egg, chick, and eggto
fledging mortalityof Black- legged Kittiw akesinWitl e s s Bay, NeWfoundland, in19 92and 1993 (Gr e a t Island , this study), and in1959 and 1970 (Gu ll Island, Maunder and Threlfall 1972). X2compareproportions of mortalitybetweenye a r s (df"ll 41 Table 2.5 Compa r isonof proportionsof l, 2, and
3-eggclutchesand meanclu tc hsizesof Black-leggedKittiwakesin1969, 197 0 , 19 8 8 , and199 0 to 1993, in WitlessBay,
New f o u nd l a nd. . .4]
Table 2.6 Meanvalu es andranges of egg length, brea d th , and volume, for Black-l egged Ki t t iwak esbr eedingin WitlessBa y , Newf ou n d l a nd , in1992, 199] (this study) and196 9 (Mau n de r and Threlfall 1972).
Standarderr orsare given for1992and 1993an d estimated for196 9 ; cri t i ca l valu e s werecalc ulated using estimated standard erro rsand det e r mi ne stat istically different means at
p=O.OS .45
xii
Table2. 7 comparison of the egg shape index of all eggs in 1992 and 1993 (this study) to all eggs, A~eggs(first laid eggs), andA~eggs
of 2-egg clutchesfrom 1969 (Maunder and Threlfall 1972) for Black-leggedKittiwakes breedingin Witless Bay, Newfoundland. Mean values, ranges, standard deviations and standarderrorsare given for 1992 and 19 93 ; standard deviationand standard error for 1969 are estimated;a critical value (Xl determines statistically different
means at p=O. 05 . 46
Ta b l e 2.6 Comparioon ofti mi n g , mean clutchand egg size, percent of nests with eggs, and hatching, fledgingand breedingsuccess of Black-legged Kittiwakes breeding on Great and Gull Islands, Witless Bay, Newfoundland, in 1969, 1970, 1986, and
19 90 through 1993 53
Tabl e 2.9 Pearson's correlation coefficientsbetween re p r o du c t ive measures of Blac k-legged Kittiwak esfromWi tl e s sBa y , New f o und l and, inth e years196 9 , 1970 (Maunder and Thre1fall1972), 1968 (Chatman 1989, E.Chatman andJ.M. Porter cited in Neuman 19 94 l , 1990, 1991 (Neuman 1994l,
1992, an d 1993 (this studyl 54
Table 2.10Summaryof percentage of young and percentage of di ffe ren tbrood sizes relative to total number of nests, for the B regions of Great
Island, in 1992 . 56
Table 2.11 Summary of percentageof young and percentage of diffe rentbrood sizesrelative to total number of nests, for the Bre g i o n s of Great
Island, in 1993 . . 57
Table 2.12 Percentage of nests with young and percentage of diffe rent br oo d sizesrelative to total numberof nests, summarized for Black -legged Kittiwakes breeding on Great Island, in
1992 and 1993 . . . 60
xiii
Ta bl e2.13 Percent of to t a l nests with young in the study plots and proportions of total nests withyoung on Great Island as recorded in island brood counts.Study plots are compared to corresponding regions of the islandand to the overall average of Great Island.na tas for study plots correspondto dates of island survey . .62 Table3.1 Fates of Black-leggedKittiwake eggsin
19 92and1993on Great Island,
Newf o u n d l a nd . . 117
Ta b l e3.2 The fates (a) and survival times (bJ of Black-legged Ki t t iw a j{e chickshatched on Great Island, Newfoundland, in
1992and1993 12 7
Table3.3 Mean laydatee of Black-leggedKittiwakes that did hatch chickscompared to laydates of kittiwakesthat did not hatch chicks
in1992anti 1993 . . 12 9
Table3.4 Comparison of hatchdatesbetween Black- legg e d Kittiwake chicks that fledged and did not fledge, and between those that lived to14 days or more and those that diedbefore 14 days, in1992 and19 9 3 131 Table 3.5 comparison of mean hatchdates of Black-
legge d Kittiwake chicks that died in the nest, disappeared, or fledgedinthe study plots on Great Island, in1992and1993 132 Table3.6 Compa risonof survival time of Black-legged
Kittiwakechicks hatching before and after insho recapel in arrival in1992 and19 9 3 13'1 Tabl e3.7 MeanDIS (du ratio nofin c uba t i on shifts)
beforeand after capelin arriva l in 1992.
and a comparisonorDIS in1992 and1993 . 136 Table3.B Comparisonof mean DeS (dur ationof chick-
re a r i n g shifts) of Black-legged Kittiwakes before and after the arrival of capelin
in199 2 . . . • . . . 140
xiv
Figure 2. 1
Figure2.2
Figure2.3
Figu r e 2.4
Figu re2.5
Figure2.6
LISTOF FIGURES
Locationof Great Islandinth e Witless Bay EcologicalReserve and locationsof the eight st u dyplot s onGreat Island . Great Island, Newfoundland, showingthe 8re g i o n s for which nest and br o od counts were summarized in the latechick stage of Black-legged Kit tiwake r-epz-oduccLori in19 9 2and199 3 . . . • • • . Comparison of the breeding performanceof Black-leggedKittiwakesin Witless Bay, Newfoundland, in1992 , 1993, 1969, and 1970. Data for1969and197 0taken from Maunder and Th r e lf a ll (1972 )
Mean egg volume (+standarder ror)according tothedateof laying for Black-legged Kittiwakesbreeding on Great Islandin 19 9 2and19 9 3.Samplesizesare shown in brackets .
Percentageof first laid eggs by dat e of Black-leggedKittiwakesbreeding on GreatIsla n d , Newfoundland, in19 9 2and 19 9 3 . La y d a t e s before4 June1993were estimated from dates in1992 (Kolmogorov- Smirnov test fo und no differencebetween distributions; seete x t) . Percentage of kittiwakenests withyoung in the8 regions of Great Island,as surveyedin the latechick stage of reproduction in1992and1993
22
32
42
4B
50
5B Figure 3.1 Numberof landings , ur.eucceeafufpredatory
at t e mp t s , an d nestsrob b ed by ne s t predators of Black -legg~dKittiwakes, in104hours of observationin Southern Cove, Great Isla nd , 1993 . . . 118 Figure 3.2 Timing of Black-leggedKittiwakeeggs
laid and depredatedinthe studyplots on GreatIsland. Newf ou ndl and , in19 9 2
and1993 . • . • . . . 12 2
Figure 3.3 Timing of th edepre da t i o n of Black.legged Kittiwake eggs fromthe studyplots in relation to the timingof Great Black- backed Gull chick hatch in1992 and 1993 on Great Island , Newfoundland. 125 Figure3.4 Chick survivorship curves for Black-legged
Kittiwakes from the study plots on Great Island,Newfoundland, in 1992 and 19 9 3 128 Figure 3.5 Mean duration of incubationand ch ick
·r e a r i ng shifts (.±standard error) of Black-legged Kittiwakesbefor eand after capelin arrival in 1992 for (a ) twonests wh e r e incubation spanned capelinarrival, and {bl fo u r nests where chick feeding spannedcapelinarrival.Sample sizes
are shown in brackets . 137
Figure 3.6
Figure3. 7
The relationshipbetween estimatedquantity of foodfe d to Black-leggedKi t t iw ake chick s per pairper hourand chickage for19 92 and 1993. Least squares linea arefitted through the data points . Feed sizeswe r e
estimated by observation . H3
Gr o wth of Black - leggedKittiwake ch icks on Great Island in 1992 th at (a) survived to fledging or near fle dg ing ,and (bl died.Each letterrepresents:adiff e r e nt ch i ck . . .
xvi,
LIST OF APPENDICES
Appendix1 Great Island,Wi t l e s sBa y , Newfoundland, showingst ationnu mber and area surveyed during broodcountsin the late c!lick stage ofBla ck~leggedKit t i wake
re p r o d uc t i o n in199 2and 1993 . 193 Appendix2 comparisonofthe timin gof breedingof
gLackcLeqqe dKitt iw ak e samo ng13 years in Wi t less Bay,Newfoundland . Records from othe r studie sare listed as
"ob serva t i o n s " . Timing of th e earliest youngin the nests was estima tedfrom these records, andare listed for
comparison . . . 194
Appendix3 Summaryof countsof atte ndedand unattended ki t t i wak e nestswith different brood sizes fo r 16observationstations, onGr eat Isl an d , in thela t e chic k stage ofre pro du ct i on , on 9and10
August , 1992 195
App e n d i x4 Summaryof counts ofat t e n d ed and unattended kittiwa ke nests withdifferent br ood sizesfor th eBreglons of Great Island, in thelatechickstage of
reprodu..:ti on, on 9and10Au gu s t, 1992 • . 196 Appendi x5 Summaryof counts of attended and
unattended kitti wakenestswithdi f f erent brood sizes fo r 16 observationst atio ns, on GreatIs l and, in the la t ech i c k stage of rep r odu c tion , on7to10Au gus t, 1993 . 197 Appendix6 Summa ryof coun t s of at t e nd e dand
unatte nde d kitt iwake nestswithdif f ere n t br ood sizes fo r theBregions of Great Is lan d , in the latech i c kstage of
re p roduction, on 7to10 Au gu s t , 199 3 . . 198 Appendix7 Food regurgi tat ed by Black- l e g gedKi t t i wa ke
chicks and ad ultsonGre a t Isl and , on 21 July and5Aug u s t ,19 93 199
xvii
CHAPTER1 INTRODUCTI ON
The importance of seabirds asind ica t ors of chenqea in the marine environment is becoming increasingly recogn ized (Fu r n e s s and Barrett 1985, 1991, Chapdelaine and Brousseau 1989, Baird 1990, Harris and Wanless 1990, Furnes s and Nettleship199 1 , Murphy et a1. 1991, Montevec c hi and Myers 1992, Monaghan et a L. 1993, Mo n t e v e c c h i 1993). Se a b i r d s are relatively easilystudied and areoftenat the top s of food chains whereth e y are vulnerable to changes th ro ug ho u t the tropic levels. Changes in marine food webs are therefore reflectedin their breedingbiology.
Some seabirds, such as the Black -l eggedKittiwake (~
~ ) ,are particularly sui tableindicator s of change (Ha r r i s and wanless 1990, Monaghan et a1. 19 9 3 , Montevecchi 1993). Kitti wakes breed colonially on cliffs, with one distinctly formed nest per pair. They are therefore easily studied and surveyed,and the contents oftheir ne s t s ca n be determined with li t tl e or no disturbance. Kittiwakes are usuallyamongthr firstspecies in a seabird colonyto reflect external chenqes in their breeding success (Hatch et al.
1993). They are small, pelagic surface feeders, faced by greater time and energy constraints than larger species (Pearson 1968, Furn essand Monaghan 1987) and are unable to pursue their prey under waterbu t depend on it to come to the su rface. They are thereforethought to be moresensitive to
food shortage (Cairns 1987, Burger and Pd att.1990, Furness and Barrett 1991 , Mont e v e c c h i 19 93) . Cl u t c h e s vary from one to three eggs and provide the potential for varying brec';,!ng effo rt an d success. This permits greater opportunity for interpretationand comparison than in seabird species with single-egg clut ches . In add i t i o n , Black-leggedKittiwakes have a holarctic distribution so that withinand between ocean c.:omparisonsare possible.
In Wi tl e s s Bay, Newfoundland, Black-legged Ki t t i wa k e s experiencedlowbreeding success in 1990 and severe breeding failu rein1991(Neuman1994). Br e e d i ngfa il u r e ofki t t i wa k e s wa s wi d e s p r e ad in Ne wf ou n dl a nd in 1991 with food shortage speculated as the cause (Casey 19 94 , Ne u ma n 19 94 ) . I t is becoming clear th a t changes are taking place in this oceanogr aphic region. Sea surface cemperaeuree during the have been colder than normal, a situation which app e a r s to be closely associa ted with pr e y sh i f t s in some seabird species, and with the maturation, spa wning and inshore movementsof capelin (Mallotus~)(Meth venand Piatt 19 91 , Mon t ev ecc h i and Mye r s 1992 ). Capelin, the main preyspecies of breeding seabirds in much of the northwest At la nt i c (BrownandNettleship 19 84 , Burger and Piatt 199 0 , Mont ev e c c h i and My ers 1992), winte r offshore and migr a t e to in shore Newfoundla nd waters to spa wnon beachesduringJune and July (Temp12 man 1948, Carscadden 1984). The in s ho re
arrival of spawningcape lin has be e ndelayed by twa to fo ur weeks in recent years (Mon t eve c c h i and Myers 1992, J.
Carscadden, DFO, St.John' s, pe r-e.ccrnm.j. Seabirdbreeding is ti me d to benefit from the usual pattern of prey availability (Lac k196 8,Pearson1968,Ashmole 1971, Fur n e ss and Monagha n 1987 ) , and therefore, ch an ge s inthetimi n g of capelinin s ho r e arrival could representase v e r e food shortage to breedingseabirds.
There has also been muc h concern ov er the gr a undf i sh fishery inth e nor thwestAtlantic in the1990s. Northe r n Cod (~ ~) stocks have drastically declined in recent years, and the fishing ind u s t r y in eastern Newfoundland was vir t u a lly shut down in1992. A fisheriesmora t o r i umco uld magnify fo o d shortage because fish offa l , which has been normally available to scavenging seabirds th roug hou t the breeding season (Pi e r o t t i and Annett 1987) , would be eliminated. Food shortage has been associated wi th an increase in predation in some studies (Be l o p ol 'skii 1957, Beaman 1978, Neuman 1994), and Herring Gulls (Larus
~) and Great Black-backed Gulls (~ marinus) , which are potential nest predators of kittiwakes , rely extensively on fish oCf a l (Threlfall 196 8, Furness 19 84, Dunnet et al. 1990, Furness et al. 1992, Ga r t he andHuppop 1984). Thus, kittiwake breeding failure due to nest pr e d a t i on maybe an indirectre su l tof general food shortage .
The object ivesof this study were to assess the breeding failure of kittiwakes in Witless Bay and to investigate its Low productivity in 1990, followed by severe and widespread failure in 1991, suggested that breeding success would continue to be poor in subsequent breeding seed shortage was predicted to be responsible for breeding failure.
Thisthesis is divided into two main sections, both of which were written to stand on their own. Chapter 2 assesses kittiwake breeding success and the tim ing of egg and chick losses in 1992 and 1993 through comparisonto previousstudiea in Witless Bay. Chapter 3 considers the causes of egg and chick mortalilty and examine a changes in the behaviour of incubating adults and those feeding chicks relat ive to the timing of the inshore arrival of spawning capelln. General conclusions are presented in Chapter 4.
1.1. REF ERENCES
Ashmole, N. P . 197 1. Sea bird ec o l og y and the marine environment.p .22 3 - 286in Farner,D. S .,King,J.T: .,and Parkes,K.C. (e da.l Avian Biol09yVol.1. A.c ad emi c Press, Ne w York.
Baird, P.H. 1990 . Influence of abio t i c factors and prey distributionon diet and reproductivesuccess of three seabirdspeciesinAl a s k a . Ornis Scand.21:224-235.
Beaman,M.A.S. 1978 .The fe edi ngan d popula tionecologyof the Great Black-bac k ed Gull in northern Scotland. Ibis 120: 126-127.
Be l op o l ' s ki i, L.O. 1957.Ecologyof sea colonybirds of the Barents Sea. rev. Akad. Nauk SSSR, Moscow-Le ningrad.
(trans latedfrom Russian byIsra elProgram forScientific Translations,Jerusalem, Israel, 19 6 1).
Brown ,R.G.B .,an dNettleship ,D.N.1984.Capelin and seabirds in the northwes t At lantic . p , 184 -194 in Nettleship, D.N.,Sanger, G.A.and Springer,P.F.Mari n e Birds:Their Fe ed ing Ecologyand Commercial FisheriesRelationsh ips. Ca n . Wil d l.se r v. Spec. Publ., Ottawa .
Burg e r, A.E. , an d Piatt,J.F.19 9 0. Flexibletime budgetsin breeding CommonMu r r e s : buf fers aga i ns t variable prey ab un dan ce.Stud .Av. Biol. 14:7 1-83.
Cairns, D.K. 19 87. Seabirds as indicators of marine food supplies.atct . Oceanogr.5:261-271.
Carscadd en, J.E. 19M.• capel in in the northwest Atlan tic . p . 170 -1 8 3 inNettleship, D.N., Sanger, G.A., andSpringer (eds.l. Marine Birds: Their Feeding Ecology an d Comme rcial Fisheries Relations hips. Can. Wildl. serv.
Spec. Publ., Otta wa.
Casey, J. 1994. Reproductive success of Black-legged Kittiwakesin the nort.hwest Atlanticin2991-2 99 3 . B.Sc.
Honours Thesis (Biopsychology). Memori al universityof Newfoundland, St . Jo hn ' s .
Chapdelaine, G. , and Brousseau. P. 1989. Size and trendsof Black-leggedKit tiwake(~ ~ )populat.ionsin uhe Gulf of at.Lawrence (Que b e c) 2974- 1985.Am. Birds 43:21-24.
Du nn e t, G.M. , Furness, R.W. , Tas ker, M.L. ,andBecker, P.H.
1990. SeabirdecologyintheNort.h Sea. Ne th e rlandsJ.
Sea Res. 26:387-425.
Fur n e s s. R.W . 19 8 4. Se a b i rd-fi s h er i e s relat.i onships in theno r t h ea s t At.lant i cand NorthSe a .p,162- 26 9in Nettleship, D, N.• Sanger, G.A., and spr inger (cds.). Marine Birds: Their Feeding Ecology and Commercial Fisheries Relationships. Can. Wildl.
serv. Spec.Publ ., ctce wa .
Furness,R.W.,and Monaghan,P. 1987. SeabirdEcology.Ch a pma n and Hall, New York.
Furness,R.W. ,and Barret.t, R.T .1985. The food requirements and ecological relat i onships of a seabird commu n i t y in nort.h Norway.Ornis Scand. 16 : 305-323.
Furness, R.W., and Barret.t, R.T. 1991. Seabirds and fish declines. Nat.Geogr. Res.Explor.7:82-95.
Furness, R.W ., Ensor, K.,and Hudson,A.V .199 2,The use of fishery waste by gull populations around t.he British Isles. Ardea80:105-113.
Garthe, S., and Huppop, O. 1994. Distribution of ship-following seabirds and their utilization of discards in the North Sea in summer.Marine Ecol . Progr. ser . 106:1-9.
Harris, M.P., and Wanless, S. 1990. Breedin g success of British kittiwa ke s ~ ~ in 198 6 ·1988:
evidence for changing condi tions in the northern North Sea.J. Ap pl. Eeol. 27:172-187.
Ha tch , S.A., By r d , G.V ., Ir on s, o.B., and Hunt, G.L. , Jr . 1993.Status and ecologyof kittiwakes (Rissatri dacty1il andR. br evirostris)inthe North Pacific. p. 140-153 in Vermeer, K., Briggs, K.T . , Mor g a n , K.H., and 51<:1gel- Causey, D. (e d e.) . The Status, EcologyandConservation of Ma r i n eBirds of the North Pacif ic.Can.Wi ldl.Servo Spec. Pub l., Ottawa.
La ck,D.1968. EcologicalAdaptations for Breeding in Bi r d s.
Methuen, London.
Methven, o.A ., and Piatt, J.F . 1991, Seasonalabun dan ce and vertical dist r ibutionof capelin (Malletos vLILoau s ) in relation to wat er temperature at a coastal site off eastern Newf o u ndl a n d.ICESJ.Ma r.Sci. 48:187-193. Mo na gh a n, P., Wri ght ,P.J. , Bailey,M.C., Uttley , J.D. , and
Wa l t o n , P. 1993. The in f l u en c e of changes in foo d abundanceon divingand surface feedingseabirds. In Mon t e v e c c h i , Ii.A {ed.L . Studies of High Latitude Homeo t he r ms : Multispeciescomparisonsof FeedingEC',-,logy an dEnergetics.Can.wildl. Ser v . occes . Pap. Mon t e ve c c hi, W. A. 1993. Birds as indicators of change in
marine pr e y stocks . p. 217-266 in Fu r ness , R.W., and Green wood, J.J.D. (eds.). Birds as Monitors of Enviro n menta l Change.Chap man &Hall, London.
Mo nt ev e cchi, W.A., and Myers, R.A. 1992. Monitor ing fluctua t ionsin pel a gic fis hav a i l a b il i ty withseabirds.
CAFSACResearch Document92/94.
Murphy, E.C., springer, A.M., and Roseneau, D.G. ~99~. High annual variability in reproductivesuccess of kittiwakes (~tridactylaJ.!.l aL a colony inwesternAl a s k a . J.
Anim. Ec ol. 60:515-534.
Neuman, J.A . 19 94. Aspects of the behaviour and ecologyof Black-legged Kittiwakes, ~ ~ ,breeding at two sites in Newfoundland, Canada, 1990-1991. M.Sc.
Thesis.Memorial university of Newfoundland,St. John's. Pe a r s on , T.H. 1966. The fe e d ing biology of sea-bird species breeding onthe Farne Islands,Ncz-thumbe z-Lend.J. Anim.
Ecol. 37:521-5 52.
Pierotti, R., and Annett, C.1987.Reproductiveconsequences of dietary specializationandswitchingin an ecological genera lis t. p. 417 - 4 4 2 inKami l , A.C., Krebs, J.R, and Pull iam, H.R. (eds.). For agi ng Be havior . Plenum Press, NewYork.
Templema.n, W.1946.Thelifehistory of the capelin ( ~
~o.f.Muller) in Ne wfoundla ndwaters.Bulletinof the Newfoundland Government Labor-atc.cy . No. 17 (Research). 151pp.
Threlfall, W. 1968. The food of three sp e c i e s of gulls in Ne wf ou nd l a nd . Ca n. Field- Nat .62: 176-1 6 0 .
CHAPTER2 BREEDING SUCCESS OF BLACK-LEGGEDKITTIWAKES ON GREATISLANDIN1$92 AND 1993
2.1 . ABSTRACT
The breeding success of Black-leggedKittiwakes (Rissa tridactyla) was investigated on Great Island, Witless Bay, Newfoundland, in 1992 and 1993, following two years of breeding failure. Fewer pairs produ ced eggs in 1992 (64\) thanin1993 (77\), and these proportionswe r e low relative to previous studies. High egg mortality in 1992 (90 \} and in 1993 (89%)and high chickmortality in1992 (9n) , but not in 19 9 3 (32%), resulted in a breeding success of 1\in 19 9 2 and 7% in1993. Timingof breeding was later than in previous years and clutches and eggs were smaller. Mean egg volum e increased slightly throughout the laying period in 1992. Volume gradually decreased in 1993. Anin c r e a s e , as notedin 1992, may indicate that food availability improved with the season. Correlations among reproductive meauurea from 7 years were high: early breeding was associated with high egg production, large eggs and clutches. and high hat ch ing , fledging and breeding success. The shape index of eggs increaseswith the age of the breeder. Comparisonof shape index among years suggested that a higherproportion of older individuals wa s breeding in years of poor productivity. This is consistent with the hypothesis thatolder individua lsare
'0
mo re able and will ing to expe nd effort and incur cost in a reproductive attempt.
Brood countsacross Great Islandin the latechick stage indicate dthatbreeding failure wa s ex tens i ve throughout the colony. Breedingsuccessvaried amo ng regions and differences were most extreme in 1992 whe n failur e wa s greatest. The areas of greatest and least successwe r e consistent between years and we r e probably related to differences in cliff structure and therefore to nest predation.
Breeding perfo r mance in study plots where adults were flushed was compar ed to studyplots assessedby observation only. No statistical diffe r ences we re found. Breeding success in eac h study plot was not different from the corresponding re g i on of Great Island, but mean productivityof allplots wa s sign if icant lylower than meanprorluctivity for Great Is lan d, emphasizing the import a nce of random or re pres entative study plots.
11 2•2• INTRODUCT ION
Breeding failure of Black-legged Kitt iwak es 1B..!.EM
~) is typical of some colonies and geographical areas in some years. In Alaska,reproductivesuccess of kittiwakes has been highly variable (Roberts19 88,Baird 1990, Murphy et al. 1991,Hatch et al. 1993). and more recently, productivity has been low in some colonies in the North Sea (Harris and Wanless 1990, Hamer et al. 1993). Ata,small, well stud ied colony in North Shields, England, breeding success was moderately high withlittle variationbe t we e n years (Thomas and Coulson 1988). Variation in success has been attributed primarily to the reliability of a stable food supply (Barrett and Runde 198 0 , Coulson and Thomas 1985, Hatch 1987, HarrifJ and wanless 1990, Murphyet al. 1991, Monaghanet; al. 1993) . At the North Shieldscolony, abundant and available foodwa s ac c e s s i b l e to kittiwakes throughout the breeding season (Coulson and Thomas 19 85 ) , whil e Alaskan kittiwakes are subject to more variable marine conditions (Hatch 1987, Baird 1990, Murphy et. ...1. 1991). Recent failures on the North Sea are attributedto food shortage because sandeel stocks (the mainpreyspeciesof kittiwakesin Britain) ha v e declined in the area in recent years (Dunnet et al. 1990, Harris and Wa n l e s s 1990, Monaghan et al. 1993). Breeding success of kittiwa kes has bee n linked to independe nt me a s u r e s of food
12 abundance in both Alaska (s p ri ng e r etet. 19 96) and in the North Sea (Aebischer et al. 1990, Hamer et ak. 1993).
Small, surface feeding seabirds such as kittiwakes parti c ula r lyvu lnerable tochang e s in food availabili tydue to time and energyco n s t r a i nt s and toaspeci a li z e dand limited feeding technique (Pearson 196B, cai rns 1987, sum eee and Monaghan 1987,BurgerandPiatt19 9 0 , Harris and Wanl ess199 0, Furness and Barrett 1991) . Kittiwakes are more ma r i ne in theirfe e d i n g habits thanar e other gull species, which are opportuni s ticand scavenge fishoffal and garbage at seaor on land (Th r el f a ll 1968), and whil';! many other gulls spend winters onla nd , kittiwakes spend non-breedingperiodsat sea (Cullen 1957). Although kittiwakes areknown to take fi sh offal, th e y are often excluded by larger species (O ' Con n o r 1974, Dunnet et a1.1990,Furness et a1. 1992 ). Thus, changes inth e breeding performance of kitt i wa k es islikelyclosely tied to changes in food availability in the marine eeceveuem.
In Witless Bay, Newfoundland, previousstudiesindicated that Black- leggedKittiwakeproductivi tywas low in1990, and severe failure was observed in 1991 (Neuman 1994). Cape lin ( ~ ~), which 1s the main prey species of breeding seabi rds in much ofthe northwestern Atlantic Ocean (Templeman 1948, .arown and Nettleship 1984, Burgerand Piatt 1990,Montevecchiand Myers 19512),havebeen delayed in their in s h o r e spawning migrationsin recent years,an anomaly which
13 seems tohe closelytie d to surface watar t:emperature (Methven and Piatt 1991, Montevecc hi andMyers 1992) . DeLayed capelln arrival or a reductionin their availabilitycould cepre sent;
a severe food shortage to breeding seabirds (Br a wl, and Nettleship1984). Neuman(1994)speculated that food shortage was in v o l v e d in kittiwake breeding failure in 1991, and probably in 1990.
The timing of breeding failure, and comparisons of repro du ct ive measuressuchas clutchsize, egg size, ti mi ng of breeding, and propo rtionsof pairsprodudngeggs, to years when productivitywas high, can be indica tiveof the timi ng and severity of food shortage. The reproductive advantagesof earlybree dingand of Lar-qe eggs and clutcheshave beenwe ll established in birds, and many stud ie s have linked these reproductive measures to food availability {Murphy et al.
19 9 4,springer et a1.1996, Cairns1997, Safinaet al.1988}.
Latebre e d ers areknown to lay smal lerclutches (Coulson and White 1961, Lack 196 8 , Perrins 1970, Montevecchi 1978, Boe r s ma and Ryder198 3 , Nelson 1988), andgenerally experience poor e r succe ss tha n ear ly bleeders (La c k 1968, Nisbet and Drury 1972, Davis19 7 5 , Ryder 1980,Toft et a1. 1984, Mart in 1987, Poole 1989, Ha r ris et a1. 1992). Timingof breed ing seems to be li n kedto food supp ly,and the resultsof numerous studies comparing reg ions or ye a r s of high and low food availabilityhan: sho wnthat theon s e t ofla yi ngcanofte n be
14 advanced throughincreased food euppt Lee,ei ther from natural variation ,orby experimentalsupplementation (Dr e nt andDaan 1980 , Martin1987, Arcese and Smit h1966). Somestudieshave shownthat early laying is associated wit hsuperior physical condition (Drentand Daan198 0 , Boersmaand Ryder 1983 ).
Different studies have reported much variat ion in the response of clu tch"sizetofood supply (Winklerand Walte rs 198 3 , Murphy et a1. 19 84, Safina et a1. 1986, Bolt on et a1.
19 92)I and studies of food supplementation have been inco n s i s t en t Jr, their results (Ar c e n e and Smith 1968 ) . However, given optimal conditions , large clutch size allows maximization of 'repz-cduot.Lve potential, and larger eggs producela r g er young (Pierottiand Annett 19B7, Bo1tonet al.
1992) and increase the Lr- probabili ty of su rvival (Parsons 1970, Pierott i 1982, Thomas 1983, Pier o t tiand Ann e tt198 7). Part of the inconsistency found in stu dies of food supplementat ionmay come from ala c k of consideration of the foodquality,an opposed to energeticcontent (Murphy et aj. 1984, B..:.~tonet al. 19 9 3), from variation in the sta te of natural food availability (Bolton et; at. 1993), and from differences between species (Sa f i n a et al. 1988) . For example, Boltonet al. (1 9 93 ) foundthat in a year of apparent food shortage, clutchesand eggs of Lesser Black-backedGulls
(l!a1 :ill1 ~) could be increas ed in size by the
supplementation of protein but not fat, and that clutch si z e
15 did not re spon d to food supplemen t at i o n in yea rs of epparencfood shortage . Simi larl y, some studi e s have fou nd differences in egg size in relat i o n to food availability (Ni s bet 197 3, 1977,Piero t t iand Bell r o s e 19 86) andso mehave not (Poole 1985. Safina et a1. 1988 ) . However. many stud i e s have demonstratedthat cl ut c h sizeinseab irds reflect s the body condit ion of the female (Nigbe t 1973, 1977, Dr e nt and Daan 1980 ,Boersma and Ryde r1983,Houat.onet al.1983,Martin 1987).
Comparisonsamongyea r s have oftenshownthat in years of poorproductivity,fewerbirds attempt reproduction(Ha t c h and Hatch :!.98 B, 199 0, Roberts 1988, Hurphyet a1. 1991, Neuman 19941. This appears tobe due tothephy s i cal body conditio n of breeders, si nce in yearswhen food availa b ility is ve ry poor, birdsmaynot attempt to breed atall (Dr e nt andDaa n 1980, Sc hr e i be r andSc hre i be r 1984,Ca i r ns 1911 7, Monte v ecchi 1993), and for so me species the r e is evide nc e that only fe ma les reaching a thresho::"d body mass will breed (e .9 ., We i mers k i r c h 1992). Drent and Daan (19801ha v e shown that body condition (measured as mass0::-muscle tissue) is a good predi cto rof breedi ngsucce ss, and corre lationbetwee nadult mas s and br eedi ng success or clutch size has be e n foun din ot he r studies (Nisbet 1913,Dre n t and Daan198 0, Mart i n 1981, Hamer et a1. 19931 . This is not surprising because bod y condition is li kel y associated with an ability to expend
as energy, which is required by processes such egg production, incubation, and chickfeeding.
I fin years of poor breeding conditions a low proportion of the population attemptsreproduction, then this proportion is predicted to represent older , more exnez-Lenced birds. Experienced birds may be more able to find and accumulate resourcesand attain the body condition necessary to attempt reproduction because foraging ability increases with age (Burger and Gochfeld 1979, Porter and sealy 1982, Furness and Monaghan 1987, Burger 1988). Older birds may also be more willing to reproduce in poor years because more effort is required and a higher risk (in terms of mortality) is involved. Since seabirds are long-lived, and assuming that reproduction is energetically expensive and represents a cost in terms of mort.. lity risks to the breeder (wooller and Coulson 1977, Reznick1985, Bryant and Tatner198 B, Nur 1988), adults are expected to protect their survival by reduced breeding or non-breedingi fcondi c Lona are poor (Ca i r n s 1987, Dunnet et al.1990). Older individuals, with less remaining potential for reproduction, are expected to accept higher risks th..n young individuals, which have many more reproductive opportunities left (pugesek 1984, 1990, Toft et al 1984, Hamer and Furness19 91 ) .
In this eeucy age of breeders was not known, but egg shapein d e xtccc.tecn196 3 ) can provide information on the age
17 composition of a breedingpopulation, and can ther efor e be used totestthepre dict i onthatahigherproport ie>nof old e r indiv i du a lswill breedin poor conditions than ingood.ones.
Egg shape inde x is a mea sur e of the ro und ne s s of the egg.
becominggrea t e rwhen theegg isre lati v e l y shor t and bro a d, an d is indepe n d e n t of the volumeof the egg (Coulson1963).
Cou lson (196 3 ) ha s sho wn that shape inde x in creaseswith the age of the female. Sha pe indexis als oas soci a tedwithlay ing order : singl e eggs, second lai d eggs in 2-e99 clutches, and C-eggs (thi r d laid) have lowestshape indic es (long and narr ow egg s). Thatsi ngle eggsha ve a lo wshapeind e x reflectsthe fact thatyoung birdstend tolay!Jing l eeggclutche s (Couleon and White 1958 ) .
A compari s on of shape ind ex between yearsof va ry i ng pr oduct i v i t y and food availabilityis predicted to reflect the assoc iatio n bet ween age of breeding birds and breed ing cond i t ions. Ifolde r bir d s repres en t ahi g her proportionof the br e e d i ngpopulation inpoo rye ars, thensha peind ex wo uld be high e r in ye ars of poorfood availabi litythanin years of abundant food supplie s . Clutch sizeis re latedto theage and expe ri en ceof bre ed ers, with older, more experi e nc e d femal e s laying lar ge r clutches (CoulsonandWhi t e 1961). Breeding conditions areals oassociatedwit h change s in clutchsi z e, andthe r e f o r esing le egg clutchesinpoor yea r s may be laid by olderindividua l s thatwouldlay two or thre e egg cl ut c he s i f
18 conditions were better. Single eggs in poor years would then also be predicted to show higher shape indicesthar,wo u l d be expected from single egg clutches in normal years.
The objective of this study was to investigate anticipated kittiwake breeding failures in Witless Bay, Newfoundland, by examiningthe reproductive measures egg size and shape, clutch size, timing of breeding, proportions of pairl3producing eggs, and egg and chick mortalities, in 1992 and 1993, on Great Ioland. These reproductive measures were compared among years, including previous studies of kittiwakes from Witless Bay, and were predicted to reflect food shortage.
The work of Maunder and Threlfall (1972) describes the breeding biology of kittiwakes on Gull Island, Witless Bay in 1969 and 1970. productivity was high in 1969 and 1970, indicating adequate food availability. These two years maybe more representative of kittiwake reproductive performance prior to recent years, and were used as a reference": to the breeding performance documented in the two years of this study. Neuman (1994) studied kittiwake breeding biology on Gull Island in 1990 and 1991, and Chatman (1989) provided informationfor198 8.
Two questions of methodology were also addressed. In any study of breeding success the studyit s e l f may influence the re s u l t s , and therefore investigatordisturbance is a potential pr ob l e m. Colon ial ne s t e r s , such as many seabirds, seem to be
19 particularly vulnerable to disturbance. Whil e solitary nestersgenerally dependon crypticne st s and.is o l a ti onfor protectio nagainst predators, colonial speciesof t e n relyon inaccessibilityof nesting areas, suchas cliffs oris l a nds . Any dist urbance in these "safe" areas may indi c at e a life· threatenlnged tueti.o n to the adultsand may therefore cause a severe re a c t i on , and because nests are dense and conspicuous. nest predators can take advantageof abandoned egge andyo u n g. Inaddit ion,becauseof thelongli f e s p a n of ma ny seabirds,ea c h breeding seasonisonl y a reLativol y small componentof theirlif e t i me reproductive success,andthe y may thereforebe selectedto respond to disturbancewi t h caution (Go t ma r k 1992). Whe n nests of kitti wak e s ar e accessedto decemdne nest conte ntsand egg size, breeding adultsinthe vicinityvacate theirnests. The effect ofth i s disturbance wa s examinedthrough a comparisonof the breedingsuc cess of plo t s wh i ch we re disturbed in this manner to plots whe r e reproduc t i ve measures wer e recordedby observation onl y.
The useof study pl ot s for the assessment of breeding success of a population mayals o cr eatea bias. For practi cal reasons, eat Ina t.eaofbreed ing success ar eoften derived from nest swithin studyplots. Whe n examined, however, variat i on between plotswi t hi n a colony can be high [Hat.ch and Hatc h 1988 ,Harrisand Wa nl e ss 1990). In 1992and 1993, I conducted island wide brood counts in the late-chi ck stage of
20 reproduction. These brood counts allowed an assessmentof variability in success across the island anddeterminedhow resultsderived fro m atudy plo t s compa r e dto ov e r all col ony
2.3. METHODS
2.3. 1. Study site and fieldschedule
This study wa s conducted on Great Island (4 7°11' N, 52°46 'W), Witl e ssBay,Newfoundland, in 1992 and19 93. Great Island is the southern most of three islands in the Witless Bay Ecological Reserve, andis located about 2j\" .~off the southea s tern shore of the Avalon Peninsula (Fi g u r e 2.1). Dimensions of theis l a nd are about 1200 x70 0m, The interior of Gr e a t Is l a n d is partially forested (fo r a detailed description of Great Island, see Net t leahip 1972) and cliffs surround most of the perimeter on which 23,229 pairs of Black-legged Kittiwakes breed (Ca i r n s et al. 1989). Oth er seabirds breeding on the island inc lude: Northern Fulmars
(EYlJr..'U:Y.§. ~), Leach 's Storm-Petre ls (Oceanodroma
~~). Herring Gulls (I&.nl..§. ~l, Great Black-backed Gulls (~ m.n.iml..§), Common Murres (!lI:i.9.
~), Razorbills (~ ~) , Black Guilemots (~
su:xllil, andAtl a n t i c Puffins (~ ~ ) .
Figure 2. 1 Location of Great Island in the Wit less Bay Ecological Reserve andlo c a tio n s of the eight study plots on Great Island.
22
23 Gr e a tIsl a nd is locatedabout 10 kmsouth of Gull{Bland (47°1S .8'N, 52°46.3' Wi Figure2.1) where previous studies of kitt iwa kebreedi ngbiologytook place (Mau nderand Threlfall 1972 , Chatma n 19 8 9 ,Ne uma n199 4 ) . Descriptions of GullIsland can be found in Ma u nde r and Threlfall (1972 ) and Neuma n (1994). On Gull Island 10,140 pairs of kittiwakes breed. Both Greatand Gull Islandsare influenced by the Labrador Cur rent,bringingcoldwa t e r southward, pastthe east coa s t of theAv alonPeninsula.
Most of June, July and Augustwere spenton GreatIslan d in 19 9 2and19 93 :fro m 20May to 28 August in 1992,and from 4 June to30Au gu s t in19 93 . In 1992, 3 days in June were spent off is la nd (2 2 Jun e - 25 June). In19 9 3 . arrivalwas dela yedbypoorweat h er,buttheis l a ndwa s visitedon 19Ma y .
2.3.2. Re p ro duct i ve performancein the study plots Sevenstudyplotswith a totalof469 nests, an d ast ud y pl ot s with atotalof 755 nestswe re monito red th r o ug hou t the br e e di n g seasonin 19 92 and19 93 , respectively (Figure 2.1). In 19 93 , the plots estab lished in 1992 were reused and expandedand plot 8wa s added. All nests considered herewere regula r lyattended byadu Lt e , at lea s t duri ng thelay i ng and incubationstageof thebreedingseaso n ,even ifno eggswere lai d.
Dat.eof laying ofea c h eg g.ct uc cnsiz e, hat. c hd a t.e, dat e of df aeppear'anc e of eggs or chicks,and approximat.efl edgi ng da t. ....ere r-ecorded for all nest.s . Plo t.1 inbot.h years and plot 2in1993 were che c ke d dailyandot.her pl o t.s , except.plo t.
7. were ch e ck ,:,d at le a s t on ce in four days, ....ee.t hec permit.ting. Plot 7,whichwas locat.:.dwithina dense He rring Gull nestingaree,wa s checked every10 days. Eggs and chicks we r e ecceeetbt e in three plots (plots 5, 6 and7) and vere mar ked for fut u r e identi f icat ion. Eg g s were ma r ke d wi t h wa t e rp r o o f pens and wereme a s u r e d (maximumlengthand breadth ) tothe nearest 0.1mm withvernier callipers . Egg volume (t he measure used fo r egg size ) was calcula ted fromthe formu la V..10.4866xbread th~x length ) , and shape indexfrom51_11 00 xbr e a d t h/lengt h), as outlined inCoul son (1963). Chick s of 2-chi c k broodswere mar ke dund er th echinwi tha snlallspot.of colourfrom a wat er;-roofpen;mass wasmea sureci.with50 ,100 , 300and 50 09 PesolaseeLee and wi ngleng t.hwas recordedwit h a stopped(wi ng ) ruler.
At plot.s 1 to 4 (in 1992 and 19 931 and B(i n 1993), re p r o d u c t i v e status was det.emu.ned by observation only and adults wi t h eggs or young in the nest never leftthe nest due to the ob s erv e r . Thus , the s e plot s also served as. «uitab l.e control pl o t s fo r thoseat ...hich eggsandchicks wer e marked andme asu red. 'ttiee e plots arerere ri-e dto as "o b s e rvaticn"
plots in analysi s or discussion of re s earcher ef fect a, and
25 r:ontrasted with "d Lst uz-bede plots whe r e ad ul t s flushed from neets wh e n e v erre p r o du ct i v e status wa s assessed.
Nes t s and plotswe r e chosen primar ily for visibilityfrom nea rbyobservation po s t s or for ac c e s s i b ilit y for egg and chic k measurements. Random choice of nests or plots was there forenot feaeible. A comparison of reproductive status between study plot s and brood counts across the is l a nd addresses the question of whether the results obtained [rom the study plata were representative for the region of the island in which the plot was located, andwhe t he r theave r age breeding succes s of the Rtudy plot s wa s repreeencac Ive of ove ra ll islandproductivity.
All cbeervecton plots (plots 1 to 4 and 8) we r ein c l u d e d in calculationsof hatc hingsuccess (chickshatchedper ~gg lai d), fledging success (c h i cks fledged pe r ch Lok hatched), and breeding success (ch i c k s fLedqedpex egg laidi in both years. In19 92 , my disturban ce seemedto have lit t l e eEff!ct onbree d i ng perf ormancein plots5,6and 7(s e a Re s ul t s) and these plot s were i.ncluded in calculations of br eed ing performance. In19 93 , Herri ng Gullsseemed ".0cue in to the opportun ity fo r pre d a t ion tha t my disturba nce created (see Di s c u s sio n ) and vis its had to be reduced t.o plots 5 and 6 laterin the season, and to plot 7 (l o c a t edwithi na dense Herr ing Gu ll col ony) throug h out the season. All data are re po rtedill pl o t summa ries,butin 1993, data fromplot7 were
"
excj.uded in calcul ation ofha tching, fledging and breeding success , an d data f:T"n plots 5 and 6 were exclud ed from cal,,:ula tior.of hatchingand fledging success.
The proportionof pai r s producingeg9s was calculatedfor each breeding season. In 199). this propo rt.io ns was calc u l atedonlyfrom plots1an d 2 (whIch were che c keddaily') be cause the rate of egg disappearan c e throughou t incub a t: i o n was high. In1992.egg predationwa s low until mosteggs had been la i d (see Cha pt e r )), and the pz-opo z-tLon of pairs producing eggs"'as cons i d e r e d reliable forall plots.
Pro::ortio n s ~, f1-and2-egg clutchesand averageclut ch size s were calcula ted fr o mclut c he s of know n siz e. Clu tch size wae conuideredunkno wn whe n a single eggwa s found for the firs t ti me on onevisitand the nest was empty in the next lindi s t urbP.dplo t s ) orwhena cl e a r view of nest contentshad Clot been oht;lined (in observa tionplots). Unknown ctuechea we r e as s i g ne d the ave zaqe clutch of that year in the calculatio nof tot a leggs laidpe r plo t .
2.3.2 .1. Timi:1gofbreeding
La yi ng distribut ions (di s t ri but i o nsofpercentageof eggs laidbydate) wer eba s e donthe layd ate s offirstlaideggs of each clutch . For ne s t s checkeddaily, layd a t ewasconsidered tobe the day an egg was found. For nestsno t checkeddaily.
laydatewas take n to be the midpo i nt betwe en visits , unless
27 hatchdate was known, Lnwhic h case laydates were ce Icu fac ed from hazchda te lbysubtrac tingmean incubation time, 27 days). Back-dating fr o m hatchdate could not be used to estimate laydate in most cases because few eggs hatched.
In 1993, my arri va l on the island was delayed until 01 June and earlyla y i ng had already begun. To est i ma t e the laydates of these earliesteggs,laydateswerecalculatedfrom hatchdatea when eggs hatched, and when 1;:99adidnothat ch, the mean laydate ofeg g s already laidon the samedate in1992was cal:. ulated and used for the la y da t e of such Elggs . Thi A approach seemed ju s t ifie d because judgi ng by the number of eggs present relativetoth e number present at that time in 19$12,andby the number ofth o s e nestswhichhad only one '?:!gg and subsequentlygained another, timing wa s very similar in the two years. Theco n d i t i o n of nests andthe behaviourof birdsonavisi t to the island on 19Ma y199 3matched clo sel y to whatwa s observed on 21 May 1992. Althoughth i s methodof eat LrnauLnq early laydates in1!')93bia s edthe earlypartof the laying distribution in 1993, analysis revealedtha t there was no statisticaldi ff e r enc e betweenthe layingdistri but ionRof 1992 and 19 9 3 (s e e Results) and this procedure th-are fore provided a good estimate of lay d a t e fo r eggs laidpri orto '1 June in1993.
Hatchdatewas consideredto be the day achi c k was found for nests checked daily. For nests not checked daily, the
28 mi d p oi n t betweenvisitswa s used . In plots wherech ickswere measured, this was refined usingchick size and the growth cu r v e s provi.ded byMaunderan d Threlfall (19 72 ).
2.3.2.2. Analy sis of dis t u r banceef fec ts
Proportions of 1- and 2-e99 clutches, and hatchi ng, fledgi ng, and breeding success were compared between observation and dist urbedplots in 1992. In 1993 , because visits to disturbedplots we re not frequentenoughduringthe hatching period to record all small c.hicks (s o me of which would have ddod or disappe aredsoon afterhatching!,hatching and fledging success wa s not compared between pl o t s . A comparison ofbreeding successbetwee nobserved anddisturbed pl o t s wa s used to test the effect of my disturban ce on breedingperformance in1993 .
As an additiona l test of theeffect ofmy disturbance , a section of accessiblecliffs south of plot5 wa s no t disturbed in 1992during regular nes t che cks. Thisareawa s surve ye din thelate incubation,earlyhatching period. and to tal nes t s, ne s t s with egg s , and nes tswith chickswe r e counted. Nest contents of thisarea we re comparedto the nest contentsin pl ot 5 on the same da y. Th i s areawa s of the same habitat type as plot5(al thoughin one section, cliffswe r e slight ly steeper and more difficult to access). and wa s there fo re
2.
cons i dered to be a sui t a blecompa r i son . In the resu l t s it19 referredto as th e control sect i o n southof plot S.
2.3 .2.3. Compari sonofrepro duct i ve successamong year s The pro p ortion ofpa irspr od uc i ng eggs,hatchingsucceas, fledgingsuccess, bree dingsuc c ess, propor tionsof diffe r e n t si z e d clut ch e s, and laying distr ibut i onswere compa r ed betwe en 19 9 2 and 1993 . Re sults from th is stud y were compar ed to reproductivemeasuresfor 1969and 1970 (Ma unde r andThrelfall 1972) . Egg morta lity (p r o p o r ti o nof eggs laid that did not hatch ). chickmo ~·tali t y (proporti on ofchicks tha t di ed ) , an d eggto fledg i ng mo r t a lity (proport i on s of eggs that didno t produce fle dg lings ) wer e report e d by Maunder and Threlf all (1 972) and were compa r e d among years of this study to det ermine ti mi ng of fail ure . Data fr om1992 and 1993wer-e combined if no statis t i c al diff ere nc e s wer e found in the s e reproduct i ve measu r es. Simila rl y, data from 196 9 and 1970 were combined i fno statis t i c al diffe re nceswere fo u nd, and the two setscf ye ars were the ncompare d. Hatching , fledg i ng and breedingsucce ss ,timi n g of breedi ng , clutch size and egg volumewere also co mpa r e d withvalues for Gull Island in1988 (Cha t man 1989) and in 1990 and '!991 (Ne uman 19 94), when possible . I t was assumed that egg measurements takenby different researche rs did not bias the comparison . Thi s seemedju st ifiedbecause met hodsofob tai n i ngegH me a surements
30 werethe same and because eggs have clear boundaries and are not dif f i c u lt to measure. Egg length, breadth, volume and shape index in19 92 and19 93 were comparedto data from1969.
The mean shape indices of all eggs,of A-eggs (first laid eggs in 1-and 2-e99clutches). and of first laid eggs in 2·e9g clutchesin 196 9 were compared to the shape indices of all eggs in 1992 and 1993.
Changesin egg volume with laydatewe r e compared to the relationship fou n d in 1969 and 1970 (Ma u n de r and Thre lfall 1972). Volumes of eggs laid on and after the median laydate were considered separatelyto test if volume decreasedinthe second half of the laying period.
2.3.3 . Broodcounts on Great l:sland duringth elat e chic k.
stage
Broodcounts were conductedem Great Island on August9 andlQ in 1992, and on August 7 to10 in 1993. Suitable dates were based on chick sizes in the study plata, sa that all chicks could be seen but none had fledged. In a givenarea (Appendix 1) , visible neet;e , nests attended by adults, and brood sizes were counted. Most areas easilyvisible from land we r e surveyed. Areas surveyed were grouped into e regions (Figure 2.2),and data were summarizedfor each.
Reproductive success, as determined from island brood counts, was compared among regions and years. Proportionsof
Figu re2.2 Great Island, Newfoundland, showingthe B regions for which nest and brood counts were summarized in the late chick stage of Black-leggedKittiwake reproduction in 1992 and 1993.
o 100 200 '---'---- ' Scaleinmeters
32
33 youngcounted per nest were comparedamong regionsandovera ll proportionswere compa r e dbet we e n years. Propor t ionsofyoung countedpe r nest were inrefere n ce to totalnests and notto atten de d nestsbecause at te n d a nc e of non-breedersand failed breede rsva riedconsiderablyon a dailybasis (unpubl.data).
The re su l t s of island brood counts were al s o used to as ses s ho w representative the study plots were of the pr od uc ti vityofthe colony. The variable comparedamongstudy plo tsand islan dsur veyswaspr o po rtionof total ne s t s wi that le a s t one yo ung . Data fr om the study plotscorr es pond toth e same date s as the isl and surveys . Studyplots were fi r st comp ared to the region of the isl a nd inwhic h the y were locat e d to test for a diffe r en ce in proport io nof ne ec e with chicks between plot and region. The overall pr opo rt i on of nests with at least one young for all study plots was then compared to thepr opor t i onfo r the entireisland, testing for diff e r encesbetweenstudy plotsand island productivity.
2.3.4. Statbticil
SYSTAT (Wi lkinson 19 90) was used for statistical analysis. Chi-s quare ana lysis us e d to compare propo rtions, the Kolmogorov-Smi rnovmet hodwasusedto compa r e laying distributi ons , Student' s t-test s compared the rel a tionsh i p sbetweentwocategorie s ofacontinuousvariable, and regress i on analy sis tested fo r seas onal tr e nds in
cont i n u o us va r i a b l e s .
34 ANCOVAwa s used to examine the relationship betwe enegg volume and laydate and year, with laydat e as a covariate; the interactiontermwa s tested for significance and i f significant. separate regressions were performed to examinethe relationshipbetweenegg volumeand laydate for eachyear. Tolerancefor type I errorwas setat 0.05 and residuals were examined for normality and independence. Means are reported±standarderror.
When multipleChi-squ are compa r i s ons were made (i nthe analysisof proportionsof 1 and 2 egg clu tchesamongye a r s and in thecomparisonof proportions of young producedamong regi ons o( Great Island),8anEerreni adjustments were made to cor r e c t the fa milyw i s e errorrate (Hays1988).
In the comparison of egg leng t h, breadth, volume and shape index bet weenthe yearsof this studyand 1969 (Ma u nd e r and Threlfall1972), a crit icalvaluewa s calculatedfor each variablefor 1969,which allowed stat i sticalcomparison . For the variables egg length,breadth and vol ume,a criticalvalue wa s calculatedfor each from the formula X= Xo- 1. 6 5(SE ) (one-t a ile d comparison; Hays 1988), whe r e
x ,
is the mean of 1969, SE is the standarderrorof19 6 9, and X isthe critical value. For each variable, the critical value for1969wa s compare dto the meansof that variablefrom 1992and 1993. If Xwas greate r than the meansof th a t vari able in 19 9 2 and 1993, the nthe mean of 196 9wa s significantlygreater than the35 means of 1992 and19 9 3 atp~O.05(Ha y s 1988) , Standard errors were not reported for 1969 and were there forecalculated using thela r g e r of the standard deviations of 1992 or 1993 (to be conservative) and the sample size of 1969. Using the standard deviation of 1992 or 1993 probablyprovided a conservative test because ranges in 1969 were smaller than in 1992 and 1993 fo rall variablesconsidered, and since eg9 measurements are normally distributed, ra n g e and standard deviation are related. For the variable shape index, a.s s(BE) was added instead of subtracted(s e e above equation)because valuesin 1992 and1993we r e predicted to be larger and not smaller than in1969, and mean shape index of 1992 and 1993 had to exceed that critical value to be statistically different from the mean shape index of 1969 atp~O.05.
2.4. RESULTS
2.4.1. Effect of res earcherdisturbance on reproductive succ essin the studyplots
No differences were observed between observation and disturbedplots~nproportionsof 1- and 2-eggclutches, an d in hatching ,fledging,and breeding success in19 92 (X·tests, p<O.OS; Table2.1). Only three chicks fledged from all study plots in 1992 and all werefrom a dist.urbed plot.. In 1993 there were no significantdifferences betweenproportions of
36
Tab le 2.1 Compar19oll of the breeding performance of Black-legged Kittiwakes in observation and di st urbed plota on Great Island , Ne wf ou nd l a n d, in 1992....nd 199).
observation distu rbed observat ion distur bed
Breeding plots plots plo ts plots
performance rvrsn ['(NI l [ \(<<)1 [lIN ) ]
l-c'J9clu tch e s ss(100 )
"
(12 6) (2S6)"
(59)2-eggcruccnec e a(IOO) aa(lUI) {2 56} u (5 9) Hatchingsuccess >0 (21 8)
,
{231} 11 (S06 ) Fledging success 0 (22)"
(2 1) ee (5 7)Breedingsu c c ess 0(:218 )
,
(::lUI,
(S0 6 ) 5(11 8) 'hatchingand fledging successcouldnot be eeeeaeedfer disturbedplots~n199).
]7
1- and 2-egg clutches or breedingsuccess in observat ionand disturbedplots (X2tests, p<O.05;Tab l e 2.1).
Nests in thecontrolsection south of plot 5 were counted on 4July 1992, in the latein c u b a t i o n per iod . Thiswas er-e first day on whichno eggs or chi ckswere found in plot5. Of 133 nestsin the area, only one nestco nt a i ned oneeggand one nest contained one small young. Both these nests we r eon a sectionwhere a steep cl i f f face madeaccessibili tydif f i cult
2.4.2 . Kittiwakebr e e d i n g perfonnance in thest u d y plotsin 1992 and 1993,and in comparis on topreviousye ars
2.4 .2.1. Breedingperformance
In sevenstudyplots and169 neace in 1992 ,64\ of pairs produced eggs, 11% of pairs with eggs producedchicks, 9\ of pairs withchicks fledged yaung , and 1%of pairs witheggs fledged yaung (Ta bl e 2.2). In19 9 3 , witha study p lot.a and 755 nests, 77\of pairs produced eggs, 17.\ of pairswith eggs la i d producedchicks, 76!1r of pairswit hchi cksfled g e d young, and9\pairswith eggs fledgedyaung (Tab le2.]).
There was no significantdifference between19 9 2and1993 in the proportionof pairs producing eg g s (X" ",O.42, p",O.64 ) and the proportion of pairs with eggs produc. ing chicks (X~1=O . 2S, p",O.62). Mare nests with ch i c k s fLedq cd yo ung
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