Publication Date

8-2016

Date of Final Oral Examination (Defense)

4-7-2016

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Raptor Biology

Department

Biology

Major Advisor

Marc Joseph Bechard, Ph.D.

Advisor

Keith L. Bildstein, Ph.D.

Advisor

Jesse R. Barber, Ph.D.

Abstract

Avian scavengers perform vital ecosystem services by removing waste and by slowing disease. Yet few details are known about the purpose or purposes of social interactions near carcasses and their role in the physical depletion of carcasses (Gangoso et al. 2013). The globally Near-Threatened Striated Caracara is a social scavenging falconid that relies on seabird colonies for food during the breeding season in the Falkland Islands, a principal stronghold in its range. The birds have been persecuted as livestock pests since the late 1800s. Although the population is now protected and remains stable, it does not appear to be growing. The caracaras’ reliance on human settlements as winter foraging grounds makes them an ideal species to examine age-stratified consumption over the entire period of a carcass’s availability. By providing and closely monitoring experimental carcasses, I estimated the mass of food consumed per bird over five minute intervals (mean 22.9 g/bird/5 min, ±1.2, SE), and found that this was negatively influenced by the time of arrival to the carcass, positively by the total numbers of birds feeding on the carcass, and positively by the proportion of the group that was adult birds. I also found that, as previously shown in Common Ravens, aggregation of a group to a carcass can be accelerated by vocalizations of the birds (Heinrich and Marzluff 1995). My data indicate that the so-called gang behavior in juvenile caracaras is very similar to that in ravens, and is an adaptive strategy to overwhelm adults at ephemeral resources and obtain food.

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