Abundance and Breeding Success as Weak Indicators of the Status of an Endemic Species

BALZA ULISES; LOIS NICOLÁS; SALOM AMIRA; PIZZARELLO GIMENA; LOIS-MILEVIVICH JIMENA; LOPEZ MARÍA EUGENIA; RAYA REY, ANDREA

Fort Lauderdale

Conferencia; Annual Meeting of the Raptor Research Foundation; 2022

Raptor Research Foundation

The fate of the breeding season in raptors is normally driven by nest site and food availability. The StriatedCaracara (Phalcoboenus australis ) is an endemic species native to the islands of southern South America. Itnests near the ground in high grasses surrounding seabird colonies, which offer the primary food source. InBahía Franklin, Isla de los Estados (IDLE, Argentina), they are associated with a Rockhopper Penguin colony ofapproximately 127,000 breeding pairs and two invasive ungulates: red deer and feral goats. We study thespatial arrangement of nesting caracaras as well as their breeding dynamics, using 69 breeding events during2014-2019. The distance to the penguin colony was the most important variable explaining caracara nestarrangement. The area of the Rockhopper Penguin colony nearest to caracara nests explained 21-38% of thevariation in reoccupation of sites and breeding success. Reproductive adults only represented 6-15% of thepopulation. The chick sex ratio was slightly biased towards females and this bias was negatively associatedwith clutch size. We could not detect any turnover of breeding pairs nor recruitment of individuals based onbanded individuals and kinship analysis. Overall, neither the local abundance nor the breeding success at thesite level would be a good indicator of the status of the species in IDLE. Specifically, interpreting individualfitness using breeding success may be spurious because of the skewed sex ratio. Considering the highabundance of floaters, there might be a shortage of breeding sites. Although ungulates may have reducedcaracara nest site availability via grazing and nest disturbance, we did not find conclusive evidence on this, asno topographic features were preferred for nesting above food availability. Individual quality, tolerance toungulate disturbance, or other behavioral traits may be driving a new dynamic in which few individuals breedin this environment.