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

Abstract

ABSTRACT 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.