Keep the chicks moving: how Sandwich terns can minimize kleptoparasitism by black-headed gulls

sandwich terns, Sterna sandvicensis, often nest in association with black-headed gulls, Larus ridibundus. The gulls provide protection against predators, but can also adversely affect the terns' reproductive success through predation and piracy of fish. To test whether leading the chicks away from the nest site is an evasive strategy used by the parent's to reduce the incidence of robbery by the gulls, we kept one group of Sandwich tern chicks at their original breeding site, while, with a wire-netting enclosure, we moved another group away from the gulls. The rate of kleptoparasitism was greatly reduced when the tern chicks were moved away from the original nest site, resulting in faster growth and earlier fledging. The rate of food parasitism and chick condition were affected only during the first 5 days of the experiment. After that, the rate of kleptoparasitism no longer differed between chicks that we moved away and those remaining in the colony. A second shift of the chicks again led to less kleptoparasitism and better chick condition. In line with these findings, the condition of free-living chicks that were lured away from their nesting site by their parents also improved. In particular, chicks initially in poor condition, which apparently suffered from high rates of kleptoparasitism, left the colony site. Free-living chicks are often lured away from the robbing gulls. However, not all subcolonies provided suitable escape routes and subsequently chicks in such subcolonies suffered from high mortality rates. (C) 1999 The Association for the Study of Animal Behaviour

Diet and foraging behaviour of oystercatchers (Haematopus ostralegus) and grey plovers (Pluvialis squatarola): The importance of intertidal flats

Many shorebirds feed on macrobenthic fauna that become available at low tide in coastal intertidal flats. Waders differ in the method used to search for food. This paper presents results of a study on the feeding behaviour, diet and energetic needs of oystercatchers and grey plovers at the Bay of Heist, Belgium, using focal bird observations and macrobenthos sampling. The two bird species differed in their success rate and foraging rate but not in their foraging efficiency. Oystercatchers spent 70.2 % of time for handling mussels and 28.6 % for worms whereas grey plovers spent 93.3 % of the time for handling worms. During the whole period of observation, 75.5% and 42.5% of prey were identified for oystercatchers and grey plovers, respectively. Of these, polychaete worms comprised 51.3% and mussels 23.4% of oystercatchers prey, and worms 41.2% of grey plovers´ prey. For both species of birds, the overall size of prey estimated was significantly correlated with the corresponding biomass (worms R2 = 0.97; mussels, R2 = 0.99). Oystercatchers obtained a total of 158.8KJ daily energy intake from mussels, worms, and grey plovers 2.37 KJ from worms only. Mussels comprised an important contribution to the total energy intake of oystercatchers and worms for the grey plovers. Habitat partitioning between the two species of birds was not observed. Keywords/phrases: Daily energy intake, Diet, Foraging behaviour, Macroinvertebrates, Shorebirds, Tidal flatEthiop. J. Biol. Sci., 10(2): 167-184, 201

Building on the concept of marine biological valuation with respect to translating it to a practical protocol: Viewpoints derived from a joint ENCORA-MARBEF initiative

Marine biological valuation provides a comprehensive concept for assessing the intrinsic value of subzones within a study area. This paper gives an update on the concept of marine biological valuation as described by Derous et al. (2007). This concept was based on a literature review of existing ecological valuation criteria and the consensus reached by a discussion group of experts during an international workshop in December 2004. The concept was discussed during an ENCORA-MARBEF workshop in December 2006, which resulted in the fine-tuning of the concept of marine biological valuation, especially with respect to its applicability to marine areas

The Influence of Diet on Mercury Intake by Little Tern Chicks

We assessed mercury levels in the feathers of little tern (Sternula albifrons) chicks from hatching to fledging and in their prey captured by adults in three main foraging habitats: lagoon, salinas, and adjacent sea. These data were used to model mercury concentration in chick feathers through food ingestion, in order to explore the effects that changes in diet would have on the mercury burden of chicks as they aged. The mercury concentration in feathers of chicks raised in sandy beaches was higher than in those raised in salinas. Lagoon prey had a significantly higher mercury concentration (0.18 ± 0.09 µg g-1 dry weight [d.w.]) than prey from salinas and the adjacent sea (both 0.06 ± 0.03 µg g-1 d.w.). In relation to prey species group, mercury content was significantly higher for bottom fish (0.17 ± 0.10 µg g-1 d.w.) than for pelagic (0.08 ± 0.06 µg g-1 d.w.), euryhaline fish (0.04 ± 0.02 µg g-1 d.w.), and crustacea (0.08 ± 0.03 µg g-1 d.w.). To understand the importance of mercury content of each prey group, we ran several theoretical scenarios assuming that chicks were fed on only one species at a time. Considering a diet restricted to lagoon (mostly benthic) prey, A- and B-chicks may encounter health problems with an excess of mercury. On the contrary, a diet restricted to marine (mostly pelagic) prey would decrease the mercury concentration in chick feathers; the fast growth rate and the related mercury dilution effect in little tern chicks seem to decrease mercury levels in their feathers. Our study supports the fact that marine pelagic prey are important for estuarine seabirds because they provide a food resource with lower contamination levels. This model may have a wider application in similar seabird species and coastal environments