Gathering Breeding and Nest Density Information

In order to model the number of individual birds (adults, eggs and nestlings) that are killed annually by roadside mowing and brushing operations, we needed to assemble breeding and nest density information for each of the focal species on the bird list (Table 2).

Table 2: Model parameter input information for birds.

Parameter Description

egg dates the earliest and latest dates on which viable eggs have been recorded in nests (Peck and James 1987:2) incubation time average # days from date of last egg laid to hatch nestling time average # days in nest after hatching

temporal distribution of egg-laying use start date regression model to determine proportion of nests initiated by date (as per Tews et al. 2009) temporal distribution of fledging assumed to be the same as distribution of egg-laying,

i.e., fixed number of days for incubation and nestling time

clutch size average number of eggs per nest

nest densities average # nests per hectare, in each of 4 general habitat types

The assumptions inherent in the parameter definitions in Table 2 are:

• 1 brood per pair and no re-nesting (as per Tews et al. 2009); most of the focal species on the list of roadside birds are known or suspected to be capable of raising second broods (killdeer, savannah sparrow, song sparrow, vesper sparrow) (Peck and James 1987), but further research is needed to gather the information necessary to incorporate this factor into the calculations of take

• 100% of eggs laid are fertile and represent a bird for the purposes of incidental take

• hatching success is 100%, i.e., the number of fledglings equals the number of eggs

• the nestlings of altricial species stay in or near the nest until fledged, and are therefore vulnerable to mowing/brushing equipment for the entire nestling period; the nestlings of killdeer (the only precocial species on the list) are led away from the nest by their parents within 2 days of hatching (Davis 1943 in Ankney 1985), travelling long distances (greater than 100 m) to brood rearing habitats (Powell 1993), at which time they are no longer vulnerable to mowing/brushing equipment

Natural mortality was not deducted from our estimates (pers. comm. C. Machtans and B. Dale, Environment Canada). The consensus was that a nestling killed by a mower constitutes incidental take no matter if that nestling would have later died of other anthropogenic or non-anthropogenic causes. These assumptions will therefore generate a maximum estimate of incidental take.

To maximize efficiency, we used the breeding information compiled by Tews et al. (2009)¹ whenever possible, i.e., for focal species that were common to both projects. For other focal species, we used Peck and James (1983, 1987) and the Birds of North America online as resources.

To determine estimates for nest densities by habitat type, we used the Canadian Breeding Bird Census (CBBC) database (see Kennedy et al. 1999) which reports adult densities (birds/km²) derived from “spot- or territory-mapping” censuses from 640 sites spread across 76 of Canada’s 194 ecoregions (Figure 1) (Blancher 2002).

Figure 1. Canadian Breeding Bird Census sites (from Blancher 2002).

For each of our focal species, we mapped the habitats in the CBBC to 4 general habitat types – Forest, Shrubland, Grassland And Wetland. For example, "grazed pasture" and "clover-alfalfa-timothy field" both mapped to Grassland, whereas "old field with hedgerows" and "tall

bottomland willow stand" both mapped to Shrubland. This both simplified and standardized the relevant habitats, and made them compatible with the Land Cover classes available to us for the GIS analysis (see Table 5, below). For provinces/territories within a species range that had no density estimates in the CBBC, we used densities from the nearest neighbouring

province/territory for which there were data. Where multiple values were available, we used the mean value. The strength of the CBBC is that it provides habitat-specific density estimates by species and by province/territory; its weaknesses are: 1) older data; 2) low sample sizes, precluding fine resolution analysis; and 3) non-random sampling sites, which make it unclear to what extent densities are representative of areas not sampled (Blancher 2002). Additionally,

1 We are indebted to Pierre Mineau, Environment Canada (Ottawa) for access to these data.

the CBBC under-represents the boreal and taiga regions of Canada (see Figure 1, above), and there are no census data for the province of Prince Edward Island.

The bird breeding and density inputs used in the simulation model are shown in Appendix C.

Further research and analysis could be done to refine these density estimates (e.g., using the approach taken by Blancher (2002)), including incorporation of data from the Northwest

Territories / Nunavut Bird Checklist Survey, and data for Prince Edward Island. Density values can easily be updated in the model if/when better information becomes available.

Accounting for Habitat Quality

Bird species that occur in roadside habitats tend to be similar to those of the adjacent habitat (Meunier et al. 1999; Belanger et al. 2006). However, road rights-of-way are probably not preferred habitat for any of the species that nest there, except possibly killdeer (Jackson and Jackson 2000). In a study in southern Quebec, species richness and bird abundance were both greater in the adjacent habitats than in the road rights-of-way (Belanger et al. 2006). Given that roadside nesting species tend to be open country birds, roads that run through closed forest habitat probably have fewer breeding birds using the roadside than those running through open habitat. Exceptions to this general rule are probably habitat generalists (e.g., song sparrow) and species that use woodland edges such as Mourning Dove and Indigo Bunting. In an attempt to address this issue, we decided to incorporate habitat quality into the analysis. For each focal species, we categorized roadside habitat as either moderate or poor quality, based on the surrounding habitat type and the habitat preferences of each species. Sources for species habitat information were Peck and James (1983, 1987), Birds of North America online, and the CBBC database (Kennedy et al. 1999). Each category was then assigned a multiplier so we could discount nest density values to account for the habitat quality factor. The

multipliers we used were 0.5 for moderate quality habitat and 0.1 for poor quality habitat. For example, if the density of savannah sparrow nests in preferred habitat was 1 per hectare, then our analysis would use half of that density for roads running through open country and one tenth of that density for roads running through forests. These multiplier values should be considered placeholders; an attempt to validate/revise them with research and expert opinion still needs to be made.

Additionally, we have allowed for some variation in roadside habitat type in our analysis. For example, a road running through open country might have a right-of-way composed mostly of grasses and herbs, whereas a road running through a forest may tend to have more of a woody component.

The combinations of habitat type and quality used for each focal species are listed in Table 3.

Table 3. Combinations of habitat type and quality for each focal species. Surrounding Habitat is the habitat through which the roadside runs, and Right-of-Way Habitat is the habitat assumed to be available to nesting birds along the roadside. Habitat Quality Multipliers are used in the analysis to discount nest densities in non-preferred habitats.

Killdeer

Surrounding Habitat Right-of-Way Habitat (Habitat Quality) Habitat Quality Multipliers

Forest 50% grass (poor), 50% shrub (poor) 0.1, 0.1

Grassland 100% grass (moderate) no discount

Shrubland 50% grass (moderate), 50% shrub (moderate) no discount Wetland 50% grass (moderate), 50% wetland (moderate) no discount Savannah Sparrow