3.4 Relative Abundance

Recommended method(s): Active nest count for swallows for relative abundance. Unlimited radius point count survey for relative abundance for all species.

3.4.1 Unlimited Radius Point Count Surveys

This technique is also used for presence/not detected surveys. Only differences from the presence/not detected survey are listed here. For details on how to conduct this type of survey see section 3.3.1

Field Procedures

• Only record swallows and swifts that are detected at point count stations during the 3 minute time-interval. Do not record birds observed between point count stations or after the 3 minute period. Any incidental observation of importance (e.g. red- or blue-listed species) should be recorded on the Wildlife Sighting Form.

Data Analysis

Relative Abundance

Relative abundance can be obtained in three ways:

• The number of birds detected per visit (i.e., the mean number of birds detected per point count multiplied by 100);
• The frequency of occurrence at the point count; and
• The frequency of occurrence of all birds detected from point counts.

A frequency of occurrence is the percentage of point counts at which a species is detected (Manuwal and Carey 1991).

3.4.2 Active Nest Count for Swallows

Counting nests is an excellent index of population size for any bird species, although it requires a great deal of effort. Ryder (1986) suggests that it is seldom possible to find enough active nests for measuring a breeding population. For most of the species in this inventory group, where information on preferred nest sites and habitats is available, generating sufficient numbers for an analysis of the breeding population (colony) is possible. It is important to realize that this is only an index to density (i.e., the number of nests per unit area). The number of nests does not necessarily reflect the size of the breeding population because there are many non-breeders (Medvin et al. 1989). It may however, be possible to assess whether a nest represents a breeding pair (is active), by watching the birds (e.g. watching for food being taken into the nest, etc.).

Active nest counts differ between individual species due to differences in nest site selection. Consequently, different searching techniques are required. These groups are: 1) Barn Swallow and Cliff Swallow 2) Bank Swallow and Northern Rough-winged Swallow 3) Tree Swallow, Violet-Green Swallow and Purple Martin 4) White-Throated Swift, Violet-Green Swallow (note this species occurs in two inventory groups) 5) Vaux's Swift 6) Black Swift.

In Table 2, the habitat and nesting preferences for swallows and swifts are given. This data can be used to aid the researcher in designing a nest survey. Nest counts are not recommended for swifts as their nests are often hidden and difficult to find. Black Swifts, although relatively common during migration, have a propensity for nesting in precipitous moist canyons thus making it very difficult to find nests (Bent 1940; Campbell et al. 1990). Consequently, there are only two nest records for all of British Columbia (Campbell et al. 1990). White-throated Swifts are often found in association with Violet-Green Swallows, and nest in the dry steep canyons of the southern interior ecoprovince (Bent 1940; Cannings et al. 1987; Campbell et al. 1990). Vaux's Swift prefers to nest in broken off, hollowed stumps, within old growth coniferous forests or big cottonwood stands (Bent 1940; Campbell et al. 1990; Manuwal 1991). The difficulty in determining nesting for this species is that the nests are placed in hollow stumps, making verification extremely problematic. Unless the potential site can be somehow accessed without destroying the nest site, surveys will not be able to accurately assess the number of nests inside a hollow stump.

Table 3. Habitat and nesting characteristics of swallows and swifts nesting in British Columbia.

Species	Habitat	Nest Location	Breeding System
Tree Swallow	Open habitat, near forest edge, often near water with standing dead trees.	In tree cavity created by woodpeckers; readily accepts nest boxes.	Highly social aggregate breeder, but not considered colonial because it defends area 10 to 15 m around nest site.
Violet-green Swallow	Open coniferous, deciduous forests, often near edge; cliff ledges. Often at high elevations.	In tree cavities, cliff ledges, nest boxes, cracks in buildings such as shingles.	Solitary or colonial depending on availability of habitat. 20 pairs have been recorded in one nest tree.
Purple Martin	Standing snags, especially near water.	In tree cavity or nest box. In B.C., all known pairs occur in managed nest boxes on Vancouver Island.	Eastern populations are highly colonial; in western part of range they are considered less colonial.
Bank Swallow	Open country with available cutbanks for nesting; near running water.	Nests are burrows dug into cutbanks along rivers or roadsides.	Highly colonial; up to 1000 pairs have been recorded.
Northern Rough-winged Swallow	Open country with available cutbanks for nesting; near running water.	Nests in burrows created by other species such as the Bank Swallow or the Kingfisher. Often nests in association with Bank Swallows.	Usually considered a solitary nester, however, recent reports of large colonies up to 300 pairs nesting in human-modified cut banks.
Cliff Swallow	Open country, near running water and highly associated with human settlements.	Nests under eaves of barns and houses, and under bridges and culverts.	Highly colonial; up to 1000 pairs.
Barn Swallow	Open country, numerous in agricultural areas; highly associated with human settlements.	Nests under eaves and on ledges, walls of barns and houses, and under bridges and culverts.	Solitary or in loose colonies.
Black Swift	In moist steep canyons.	On cliff ledges and in crevices.	Nest in small colonies. Colonies have not been recorded in B.C.
Vaux's Swift	In old growth forests? Often preferring cutover areas or burns which have left snags.	Inside a hollow tree; often up to 20 pairs. Very few natural sites have been recorded in B.C.; most are reports of nesting in chimneys.	Nest in small colonies.
White-throated Swift	In dry steep rocky canyons of the southern interior.	On cliff ledges and in crevices of precipitous cliffs.	Highly colonial.

Office Procedures

• Review the section, Conducting a Wildlife Inventory, in the introductory manual, Species Inventory Fundamentals (No.1).
• Obtain relevant maps for project and study(s) (e.g., 1:50 000 air photo maps, 1:20 000 forest cover maps, 1:20 000 TRIM maps, 1:50 000 NTS topographic maps). At minimum 1:50 000 map of region is needed, so that study areas can be delineated.
• Determine Biogeoclimatic zones and subzones, Ecoregion, Ecosection, and Broad Ecosystem Units for the project area from maps.
• Identify potential survey strata. Select study areas from the strata that are likely to have suitable swallow nesting habitat.
• Consult the British Columbia Nest Records Scheme for possible nest locations and information.
• Contact all landowners prior to surveys and request permission to trespass on their land.

Sampling Design

• Varies by species groups as outlined below.

Barn and Cliff Swallows build mud nests which are highly friable, thus they must place them in locations protected from rain or run off water. Both species select protected nest sites under eaves and bridges and inside old buildings and culverts (Bent 1942; Gauthier and Thomas 1992). They nest almost exclusively on artificial structures in human environments (Erskine 1979).

• Nest counts: Methods for determining nest densities will depend on where the survey is done. Regardless of whether the focus is on suburban or rural populations, stratify the habitat based on expected densities. For example, structures such as barns or bridges could be placed in a high strata; parks, schools, and vacant lots could be put into a medium strata; and suburban neighbourhoods in the lowest strata (based on percentage of open area to suitable nest sites). Communication with farmers, homeowners, shopowners, and the local police should precede the survey as a precaution, and also for gathering further population information. Farmers and homeowners especially, often know what species are nesting on their property, and the more interested ones will keep a watch for further nesting activity.

Bank and Northern Rough-winged Swallows naturally nest in burrows within cutbanks of rivers and streams. They too have benefited from human activities (Erskine 1979; Weeks 1987; Moller 1989) such as extensive rock quarrying and road building which has created gravel pits and cut banks allowing for easy burrowing (nest building).

• Nest counts: Colonies can be located by following river courses and roadways in areas where the soil conditions allow for easy burrowing in the cutbanks. It might be practical to stratify quadrats by the length of river or roadways running through the quadrat. After talking to local naturalists, cruise all roadways, gravel pits, and river systems to identify nest sites. Since a burrow may be unused in any given year, the criteria for establishing occupancy are the presence of chicks, fledglings, or adults at the burrow entrance, claw marks outside of the burrow, or lines of faeces outside of the burrow (Jones 1986; Garrison at al. 1989). Unused burrows often have vegetation growing out of them or cobwebs hanging across the burrows entrance. The contents of nests of Cliff, Bank and Northern Rough-winged Swallows can be determined using a flashlight and a dental mirror.

Purple Martin, Tree Swallow and Violet-green Swallow all are cavity nesters and use natural snags and artificial nest boxes throughout their range. Violet-green Swallows also nest in the cracks and crevices of buildings. Traditionally, they are hole nesters which have depended on other species such as woodpeckers to provide cavities for nest sites. They have also benefited from direct intervention by humans through placement of artificial nest boxes in open habitat (Erskine 1979; Lumsden 1986). The Purple Martin especially, has benefited from artificial nest sites, but most successfully within the eastern part of its range. Southern British Columbia is the northern extent of its western range, with only about 50 breeding birds all confined to artificial nest boxes (Siddle et al., in prep.).

• Nest counts: Focus on snags or live trees which contain cavities formed by woodpeckers and sapsuckers. Habitat can be stratified (based on expected densities) using a ratio of open habitat (agricultural fields, open water) to snag density. For example, one could assume a continuum from completely open habitat (0%) to completely forested habitat (100%). A plausible stratification may be < 5% or > 70% habitat as a low strata, 30% to 70% as medium strata, and 5% to 30% as high strata. These numbers are only suggestions, and preliminary surveys are required for proper sampling.

Sampling Effort

• Will depend on the extent of the survey area to be searched.

Sampling Standards

• Weather: Nest surveys can go ahead under all reasonable weather conditions, except during rain or when it is unseasonable cold, since the process will flush the parent from the clutch exposing the eggs to the weather.
• Time of year: Conduct surveys from the last week of May till the first week of July.
• Time of day: Nest surveys can be conducted after 09:00 hours because female is laying before then.

Personnel

• Surveys should be conducted by a biologist with prior experience in bird surveys, and an expert in swallow and swift species identification.
• An assistant should be hired to assist in nest searches to permit more area to be covered.
• At least one person should be familiar with the collection of habitat data.

Equipment

• Binoculars (minimum 7X) and a spotting scope (minimum 15X)
• Field note books and data forms
• Compass
• Ladder
• Nest checking mirror
• Flashlight

Field Procedures

• Search study areas for Barn Swallows and Cliff Swallows.
• Old buildings, eaves of houses and barns, inside culverts, under bridges and other areas which provide a combination of cover from rain and access to flight paths.
• Nests are mud structures plastered against the walls of these structures.
• Search study areas for Bank Swallows and Northern Rough-winged Swallows.
• Cut banks along roadsides, train tracks, rivers, lakes, gravel pits, sawmill-sawdust piles.
• Nests are placed at the end of burrows which are dug into the sides of cutbanks.
• Nests are considered active if there are fresh claw marks at the entrance of the burrow, lines of faeces below the burrow, an adult present or a chick present.
• Nests are considered inactive if there are webs, or vegetation growing across the entrance to the burrow.
• Search study areas for Violet Green Swallow, Tree Swallow, Purple Martin.
• In natural areas, check snags where the cavity is not obscured by vegetation and the immediate surroundings are open (e.g., natural clearings, beaver ponds etc.).
• To ascertain occupancy of a hole, tap on the snag with a stick to bring the swallow to the entrance for identification.
• In human landscapes, check natural cavities in fence posts, buildings and other structures; also check artificial nest boxes.
• When a colony/nest is found follow the appropriate protocol below.

Complete Colony / Nest Count

• At each colony record its location (UTM), area, and habitat information. If only a solitary nest is found record its location (UTM), area, and habitat information.
• For each nest observed: record the species, number of birds present, their age class and sex, and the appropriate nest description information.

Partial Colony Count (if a colony is too large to count every nest)

• Estimate the total number of nests in the colony (active or not).
• Choose a representative Sample Plot(s). Describe its location within the colony and record its area.
• Estimate the proportion of the colony that the Sample Plot occupies.
• For each nest in the Sample Plot(s): record the species, number of birds present, their age class and sex, and the appropriate nest description information.

Data Analysis

• Relative Abundance: # of active nests per unit area.