Nesting ecology and reuse of nest burrows by Bank Swallow (Riparia riparia) in southern Yukon

Bank Swallow (<i>Riparia riparia</i>) is a declining insectivorous bird that nests colonially in near-vertical surfaces, including natural banks along waterways as well as those created by industrial excavation. Several threats are likely contributing to the population decline, conservation measures have been recommended, and monitoring methods have been developed. However, little is known of this species in the extensive boreal portion of its breeding range. To assess whether recommendations developed in southern areas are likely to be effective in a more northerly region, we investigated aspects of the nesting ecology of Bank Swallow in southern Yukon during 2013–2017. Nesting activity occurred between 20 May and 21 August. We found an exceptional abundance of nest burrows in natural riverbanks along 46 km of the Yukon River near Whitehorse (326 burrows/km), but relatively low percent burrow occupancy in both natural and artificial habitats compared to studies from other regions. Year-to-year persistence of nest burrows and rates of reuse of burrows were high compared to other studies. We highlight the potential importance of the boreal region for recovery of Bank Swallow in Canada, and the importance of using region-specific estimates of percent occupancy when monitoring Bank Swallow using burrow counts. Further study is needed to determine whether unoccupied burrows contribute to nesting success, and whether there are situations in which Bank Swallow burrows should be protected year-round instead of only during nesting.

Reproductive success and health of breeding Bank Swallows (Riparia riparia) in aggregate (sand and gravel) pit and natural lakeshore habitats

Bank Swallows (Riparia riparia) are designated as Threatened in Canada, in part due to loss of natural breeding habitat along lakeshores and rivers. Excavation in sand and gravel pits (aka aggregate pits) has increased availability of potential nesting habitat away from lakes and rivers, and these substitute habitats may be important to stabilize the decline experienced by some Bank Swallow populations. Over 2 yr, we collected data on Bank Swallow reproductive success from 2 natural lakeshore habitat sites along bluffs of the north shore of Lake Ontario and 7 aggregate pits in southern Ontario, within 100 km of the lakeshore. Nests at the lakeshore habitat were initiated earlier than in aggregate pits, 8 days earlier in 2014 and 13 days earlier in 2015. Neither clutch size nor number of nestlings were different between the 2 habitat types. There were differences in the number of fledglings produced between the habitat types, with Bank Swallows nesting in aggregate pits raising more fledglings per successful nest. However, birds nesting in aggregate pits also had significantly more nests that raised no fledglings, even though eggs in those nests hatched. Breeding adults from aggregate pits were initially heavier than those from the lakeshore habitat, but their mass decreased significantly over the nesting season. Fledgling masses were not significantly different between habitat types. Parasite loads on fledgling Bank Swallows from aggregate pits were significantly lower than on fledglings from the lakeshore. These indicators suggest that aggregate pits can provide at least equivalent habitat for Bank Swallows to that provided by natural lakeshore habitat, making them potentially key for the recovery of this species in Ontario.