Long-term trends (1989-2013) in the seabird community breeding in the lagoon of Venice (Italy)

The community of seabirds breeding in the lagoon of Venice, one of the largest around the Mediterranean, was monitored over the 1989-2013 period. Six species have been recorded (<em>Larus michahellis, Chroicocephalus ridibundus, Larus melanocephalus, Sternula albifrons, Sterna hirundo, Sterna sandvicensis</em>). Over the study period, 346 colonies were surveyed; they were located on saltmarsh islets, dredge islands and other artificial sites, in descending order of importance. Beaches were used only at the beginning of the survey. About 4,900 pairs bred in the 2009-2013 years. The community has been always dominated by <em>L</em>. <em>michahellis</em>; in the 2009-2013, this species and <em>S. sandvicensis</em> comprised about 70% of the total. The longterm trends show moderate increase in the size of the whole community. Contrasting trends were observed in different species, with <em>L. michahellis</em>,<em> S. albifrons</em> and <em>S. sandvicensis</em> stable or increasing, whereas <em>C. ridibundus</em> and <em>S. hirundo</em> were declining. The number of pairs nesting on artificial sites increased over the last 15 years, while those on saltmarsh islets decreased correspondingly. This was possibly a response to the increase of mean sea level and storminess observed in the last twenty-five years. <em>S. albifrons</em> and <em>S. sandvicensis</em> populations reached national importance; the population of the latter species is noteworthy at a Mediterranean level.

Foraging Decisions of Sandwich Terns in the Presence of Kleptoparasitising Gulls

We studied prey selection of Sandwich Terns (Sterna sandvicensis) in the presence of kleptoparasitising Black-headed Gulls (Larus ridibundus) on Griend, Dutch Wadden Sea, from 1992 to 1998. Most often, gulls robbed larger sandeels rather than herring from terns. Provided that one parent attends the chick, energy intake would be too low for the chicks' survival if exclusively fed on sandeel. By provisioning an increasing proportion of herring, parent terns could theoretically overcome a potential food shortage when the chicks grow older. However, the proportion of herring did not increase with age of chicks in most years. Instead, parents increased their foraging effort with the growth of their offspring. In years with high proportions of food loss, parents left their chicks unattended at the nest more often. In that way, parents were largely able to counterbalance food shortage of offspring. In 1992 and 1996, when diet composition was unfavorable and food losses to gulls were high, parents left their chicks unattended at the nest for ∼80% of the daylight period. It is argued that the present working level of parents might be higher than in the 1960s.