Breeding biology of American crows in Saskatchewan parkland habitat

Abstract

The breeding biology of American crows (Corvus brachyrhynchos) was studied in two areas (St. Denis and Elstow) of aspen parkland habitat in Saskatchewan, Canada, in 1987 and 1988. The St. Denis area had relatively more diverse land use and contained more wetlands than the Elstow area. Crows returned from winter ranges in early April and were frequently observed at breeding sites in late April, when nest building began. Overall, mean (± SD) clutch initiation dates were 6 May (± 6 days) at St. Denis and 10 May (± 6) at Elstow, but, in 1988, clutches were initiated about 6 days earlier at St. Denis than at Elstow (P < 0.05). Density of nests at St. Denis averaged twice that found at Elstow (0.70 and 0.35/km2, respectively; P < 0.05). Size of incubated clutches did not differ between years or areas, and averaged 4.8 ± 0.6 eggs (n = 104). Hatching success did not differ by year or area, but in 1987, nests at St. Denis produced nearly twice as many young as at Elstow. Brood losses resulted from predation, starvation, and possibly other factors. Chicks in smaller broods gained mass faster and fledged at a lighter mass than chicks in larger broods. There were no consistent differences between areas in the mass, bill length, and head–bill lengths of 22-day-old chicks. Young fledged when they were between 30 and 34 days old. Crows at St. Denis had higher reproductive success (1987), nested at greater densities (1988 and both years combined), and began egg laying earlier (1988) than at Elstow, suggesting that St. Denis was a more productive breeding habitat.