Intrinsic and extrinsic factors affecting foraging behaviour of breeding Mediterranean Gull (Ichtyaetus melanocephalus)

Gulls (subfamily Larinae) are a cosmopolitan group of seabirds, and as such they have peculiar biological traits like colonial breeding, high longevity, low fecundity, biparental care, sexual maturity reached over many years. Moreover they stand out for their generalist nature, both in their methods of locomotion (flying, swimming and walking) and in their foraging behaviour and diet. They are therefore opportunistic species that, being able to use both terrestrial, coastal and marine habitat, constitute a link between marine and terrestrial trophic webs. Moreover, it is common for them to exploit food sources that derive from human activities, like agriculture and fishery. In this study 17 adults of Mediterranean gull (Ichthyaetus melanocephalus) were fitted with GPS devices to follow their movements during different breeding seasons (2016, 2017, 2022), and in two different places a few km from the coast of Emilia Romagna: the saltpan “Salina di Cervia” and the wetland of Ortazzo. This approach has never been applied to this species, which is less studied and known than other gull species. The aim of the study is to assess the type of foraging behaviour of this species during the breeding season, and in particular to verify which factors affect it. In this study I analyzed some foraging trip metrics (maximum distance from the nest, duration) and the proportion between number of fixes at sea and on land of each trip, in relation to features of individuals and some marine meteorological variables. Results show that males make trips that have the same length as the ones of females, but with a longer duration, and that parents reach longer distances during chick rearing than during incubation, but with the same trip duration. The probability to forage at sea is higher for males, and increases with the passage from incubation to chick rearing. This probability shows a peak late in the morning while it is smaller in the other periods of the day; furthermore it is higher during working days than during weekend. Mediterranean gulls also seem to prefer a calm sea and an intermediate wind speed to go to the sea. The colony identity, instead, seems not to have a role in determining their usage of the sea. Foraging tactics of these individuals therefore is given by a combination of intrinsic (individual characteristics and breeding stage) and extrinsic (environmental variables) factors. This type of study is important because it allows to obtain useful information for management and conservation of the target species by increasing our knowledge about its habits. Moreover, its application to other seabird species has already demonstrated that it is possible to obtain indications about the status of surrounding marine environment by studying their ecology, thanks to their important role as sentinel organisms.