Cannibalism of nestling American kestrels by their parents and siblings

Abstract

We examined the frequency of cannibalism of nestling American kestrels (Falco sparverius) in north-central Saskatchewan. We investigated human disturbance and food shortages as possible causes of it. Cannibalism of nestlings by their parents and siblings was confirmed by observation and by the presence of partially eaten carcasses, or inferred from the sudden disappearance of a nestling between frequent nest checks. Cannibalism occurred at 8% of 48 nests in 1988, and 18% of 92 nests in 1989. Not all nestlings that died were cannibalized. Where nestling mortality occurred, carcasses were eaten in at least 20% of nests in 1988, and 63% of nests in 1989. The chicks that were cannibalized died at a significantly younger age than those that died but were not cannibalized. The mass and age of the parent and the laying date were not associated with the occurrence of cannibalism. We found no strong evidence of a causal link between human disturbance and nestling mortality or cannibalism; however, the abundance of small mammal prey was inversely related to the frequency of cannibalism between years, and there were fewer prey and lower prey delivery rates in territories where cannibalism occurred than in territories where nestling mortality did not occur. The fact that some nestlings died but were not eaten suggests that such mortality was unrelated to food shortages. The food advantage of cannibalism may not outweigh potential disadvantages such as disease transmission.

Sex-specific associations between reproductive output and hematozoan parasites of American kestrels

“…Voles, the main prey of kestrels on our study area, were more abundant in 1994 than in 1995 (Dawson and Bortolotti 2000b). Although parasite loads do not appear to be related to food abundance (Dawson and Bortolotti 1999), reproduction by kestrels is highly dependent on food supply (e.g., Bortolotti et al 1991;Wiebe and Bortolotti 1992, 1995 and kestrels may have been under more stress during egg laying in 1995. Nonetheless, our results may be conservative because we tested for relationships between parasitism and only one component of reproduction, namely egg laying.…”

Genetics, local environment and health as factors influencing plasma carotenoids in wild American kestrels (Falco sparverius)

“…Studies of our kestrel population have shown that the abundance of voles has an impact on the growth, condition and survival of nestlings (Bortolotti et al 1991;Wiebe & Bortolotti 1994, 1995. Therefore, the lower carotenoid levels in adult kestrels at nests with more voles suggest a potential trade-o¡ between diet quality and quantity.…”

Sexually dimorphic eggs, nestling growth and sibling competition in American Kestrels Falco sparverius

“…American Kestrels are small falcons that have been the recent focus of laboratory-and field-based work Functional Ecology 1997 11, 331-335 on reproductive behavioral ecology (Bortolotti, Wiebe & Iko 1991;Wiebe & Bortolotti 1992Anderson et al 1993a, b;Wiebe & Bortolotti 1994, 1995Wiebe 1996). We used the egg dimensions of 170 kestrel nestlings from five-egg clutches (the modal clutch size in the wild) produced in 1990 and 1991 in the captive breeding colony at the Avian Science and Conservation Centre, McGill University, Montreal, Canada, to test the hypothesis that mothers favour son function with larger eggs.…”