A study of nesting sparrowhawksAccipiter nisususing video analysis

Abstract

Capsule Chick age influenced female prey size and the provisioning rate of each parent while rainfall increased female brooding in a single sparrowhawk territory in Edinburgh. Aims To study the details of prey delivery, female brooding and the factors affecting chick mortality in a single sparrowhawk territory in Edinburgh. Methods Video footage collected from a sparrowhawk nest in the Royal Botanic Garden Edinburgh in 2011 and 2012 was used to record the occurrence and size of prey deliveries by each parent and the time spent brooding by the female, with respect to the age of the chicks and daily rainfall measurements. The results were compared to observations made at three nests in Ae Forest (southwest Scotland) by Newton [1978. Feeding and development of sparrowhawk Accipiter nisus nestlings. J. Zool. 184: 465-487]. Results Once the chicks were four days old, the total number of prey deliveries per day did not change with age. However, there was a corresponding decrease and increase in provisioning rates by male and female parents, respectively, although the male contribution remained highest throughout. In the late stage of the nestling period, the higher food requirement of the chicks was matched by an increase in female prey size. The total rainfall per day had no effect on the rate of prey deliveries by either sex but did cause a rise in the time spent brooding by the females each day. A higher frequency of smaller prey deliveries and more extensive female brooding and prey partitioning occurred at both nests compared to those studied by Newton [1978. Feeding and development of sparrowhawk Accipiter nisus nestlings. J. Zool. 184: 465-487]. Conclusion The study nests were probably in a particularly high quality sparrowhawk territory and wetter weather may have been the primary reason for the reduced reproductive success in 2012.

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“…Most likely this reflected the chicks being provisioned away from the view of the webcam rather than an actual decrease. Similarly increased provisioning of nestling raptors is widespread where prey availability is sufficient to meet the chicks' demand, either via increased rates of delivery or the delivery of larger prey (e.g., Watts 2014). At their highest, the rates of prey delivery we observed are slightly lower than Laing's (1985) estimate of 9.6 deliveries per day across the nestling period for Merlin nests in Denali National Park, Alaska.…”

“…Attendance declines substantially once the nestlings reach thermoregulatory independence (Holthuijzen 1990, Katzenberger et al 2015, Keeley and Bechard 2017. The species' body size and rate of development modify the chicks' time to homeothermy and the associated drop in the adults' brooding, but brooding varies in response to weather such as rain and abnormally cold or warm temperatures (Watts 2014, Katzenberger et al 2015. Our observations align with expectations in terms of parental roles during the nestling phase, but the suggestion that Merlins attain homeothermy by D7 (Warkentin et al 2005) may be too optimistic, given the continued brooding past D7 that we observed.…”

“…Studies of diverse raptor species over the past three decades using these technological approaches have assessed variation in nesting behavior and provided insight into raptors' capacity for adaptation to, or mitigation of, varying environmental conditions (Palmer et al 2001, Watts 2014, Katzenberger et al 2015. Outcomes have ranged from baseline descriptions of nesting behavior, as for the Mexican Spotted Owl (Strix occidentalis lucida; Delaney et al 1999), Eurasian Kestrel (Falco tinnunculus; Steen et al 2012), and Northern Saw-whet Owl (Aegolius acadicus; McCullough and Conway 2017), to detailed assessments of intersexual differences in nesting behavior of adults and the effect of nest-site quality on parental care, as for the Ferruginous Hawk (Buteo regalis; Keeley and Bechard 2017) and Gyrfalcon (F. rusticolus; Henderson et al 2021).…”