Estimating predation on breeding European storm‐petrels ( Hydrobates pelagicus ) by yellow‐legged gulls ( Larus michahellis )

Abstract

Several hypotheses about changes in adult survival of European storm‐petrels Hydrobates pelagicus and predation by yellow‐legged gulls Larus michahellis at Benidorm Island (western Mediterranean) during 1993–2003 were assessed. Two approaches were used: analysis of pellets containing remains of predated petrels from two caves, and multistate capture–recapture models using recaptures of breeders together with recoveries only from one of these caves. These models were used to estimate separately adult storm‐petrel survival and a minimum probability of being killed by gulls. At least 11–14% of the storm‐petrels killed had been ringed as breeders. Local adult survival varied greatly among years, from 0.701 (se=0.095) to extremely high values (0.951, se=0.031) for such a small species (0.833 on average for the whole period). Nevertheless, it was not possible to assess whether this variation was influenced by inter‐annual differences in gull predation. The peak of predation occurred in June, when maximum numbers of prospecting petrels visit the colonies. Predation was much higher at the cave that received stronger illumination from Benidorm city. Minimum predation probabilities estimated from capture–recapture varied with time from 0.022 (se=0.011) to 0.040 (se=0.016), and increased significantly after the powering of light received from the city in 1997. In these years, predation by yellow‐legged gulls accounted for a large percentage of mortality of storm‐petrels at Benidorm Island (up to 33%). Both methodological approaches confirmed that predation was carried out by specialist gulls, and that neither the size of the gull colony nor its food availability influenced predation on petrels. Management might reduce predation rate by removing gulls that nest in the caves, since these individuals tend to kill most storm‐petrels.

An invasive gull displaces native waterbirds to breeding habitats more exposed to native predators

“…This contrasts with the data from other related, large gulls, especially the closely related yellow-legged gull Larus (cachinnans) michahellis. In the Mediterranean, this species is an important predator on the eggs and chicks of many seabirds, some of them endangered (Vidal et al 1998;Rusticali et al 1999;Hernandez-Matias and Ruiz 2003;Oro et al 2005). It is also a very strong rival and competes successfully with other, smaller seabirds for breeding sites (Oro et al 2009), which is in agreement with our results.…”

Methods for detecting and quantifying individual specialisation in movement and foraging strategies of marine predators

“…Pierotti & Annett 1991, Annett & Pierotti 1999, Oro et al 2005, Hamer et al 2007). For example, by observing prey items being delivered to pigeon guillemot Cepphus columba chicks for an average of 4 full days over multiple years, Golet et al (2000) defined specialists as individuals whose diet contained more than 50% of a particular item or class of items.…”

Uso del espacio por adultos de gaviota patiamarilla Larus michahellis Naumann, 1840 durante el periodo reproductor: resultados preliminares en relación al uso de vertederos.

“…Por ejemplo, varias especies de gaviotas en todo el mundo han incrementado el tamaño de sus poblaciones muy significativamente (Olsen & Larson, 2004). Tal incremento ha generado, en ocasiones, la aparición de problemas ecológicos, sanitarios, sociales o económicos (Raven & Coulson, 1997;Barras & Wright, 2002;Oro et al, 2005;Oro et al, 2013). La gestión del binomio vertederosgaviotas se ha convertido, en consecuencia, en algo prioritario para las administraciones y organismos gestores de residuos sólidos urbanos (Smith & Carlile, 1993;Harris & Wanless, 1997).…”