Multispecies colonies of wading birds frequently occur in both freshwater and estuarine environments, in locations with potentially safe places for nesting where the nearby shallow waters provide food for rearing chicks. In 2011/2012, we investigated the feeding ecology of two large-sized waterbirds, the great egret, Ardea alba, and the roseate spoonbill, Platalea ajaja, which breed sympatrically in limnetic and estuarine colonies 65 km apart in southern Brazil. Whole blood from chicks was sampled for d 13 C and d 15 N stable isotopes, and their diets were assessed using direct (conventional) methods. The diet of spoonbills consisted of fish, insects, crustaceans, mollusks, and seeds, whereas great egrets fed mainly on fish, insects, and crustaceans. Bayesian stable isotope mixing models indicated that spoonbills fed exclusively in limnetic habitats, regardless of where they bred, whereas egrets breeding in the estuarine colony fed on both estuarine and limnetic prey, expanding their isotopic niche considerably. Dietary data confirmed this result, with the diets of egrets in the freshwater colony showing high similarity to the diets of spoonbills in both freshwater and estuarine colonies. The isotopic niche overlap was the lowest between species in the estuarine colony, suggesting that the feeding plasticity of egrets reduces interspecific competition during breeding.

Foraging habitat selection by gull-billed tern (Gelochelidon nilotica) in Central Spain (Castilla-La Mancha). The gull-billed tern breeds in temporary lakes in Castilla-La Mancha in Central Spain but depends on surrounding land habitats to feed its chicks. It is therefore vital to know the type of environments it selects to capture prey to feed nestlings. The aim of this study was to evaluate the use of habitats for hunting by adult gull-billed tern. Of 66 lakes monitored between 1996 and 2016, we found the gull-billed tern used 12 for breeding. Each lake was used during this period for 1-14 breeding seasons. We selected circular areas around the three wetlands where the species bred in 2013 and 2014. Within these circles, we sampled a total of 60 random points and recorded 125 gull-billed tern contacts (including between 1 and 39 birds). We estimated the same environmental variables at contact and random points, including land use and the distance to the nearest wetland, the nearest colony and to several types of anthropic uses (paved roads, houses, and cities). To evaluate habitat selection we calculated the Manly selection index for soil use variables, and fitted linear mixed models to evaluate differences in the distance variables. Land uses selected for foraging by the gull-billed tern were mainly cereal crops, whereas vineyards were avoided. The birds foraged on average up to 2 km from the colonies and tended to avoid proximity of towns and paved roads, suggesting that the species is sensitive to human disturbance. Vineyards are the main land use in this region and the intensity is increasing. Our results suggest vineyards should be limited in areas around these wetlands so that gull-billed terns may forage in their preferred sites.

Rice fields and waterbirds are an example of a synergy that can occur between agriculture and conservation. This connection is especially relevant during the farming period, when nesting waterbirds need to obtain resources to cover their energy requirements and those of their chicks in rice fields. However, new farming techniques may potentially put fulfilling this role at risk. Studies on how species use rice fields to feed during this critical period are essential to understand waterbird population dynamics and to optimize conservation measures. At present, several species of colonial birds in l’Albufera de València (Spain) that depend on trophic resources available in rice fields have decling populations and decreases in productivity. We therefore assessed trophic niche segregation in the diet of chicks of a waterbird community composed of seven species through stable isotope analyses of carbon (δ13C) and nitrogen (δ15N) obtained from chick blood and tissue samples of potential prey. According to trophic niche widths, chicks of Black‐headed Gull Chroicocephalus ridibundus and Gull‐billed Tern Gelochelidon nilotica showed a similar diet, although Gull‐billed Tern had a major trophic specialization. The Western Cattle Egret Bubulcus ibis fed its chicks in a wider range of different habitats, with organisms located at the base of the food chain and with a greater importance of terrestrial prey than other species. Conversely, the Glossy Ibis Plegadis falcinellus had a more differentiated diet, mostly in freshwater habitats and mainly consuming odonates. Grey Heron Ardea cinerea, Little Egret Egretta garzetta and Squacco Heron Ardeola ralloides showed overlap between their niches, largely explained by the presence and abundance of cyprinid fish and odonates in their diets. Our results suggest a less important role than expected of Red‐swamp Crayfish Procambarus clarkii, and a more important role of odonates despite being a less energy‐rich prey. In conclusion, the diet of generalistic species of waterbirds in this study suggests that their trophic niches can overlap when relative prey abundance is high.