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This study reports on the diet of breeding West African Crested Terns Thalasseus albididorsalis on the basis of otoliths found in excrement (a mixture of pellets and faeces near nests). During the period 1998–2019, towards the end of the incubation period, excrement samples were collected from breeding colonies on islands, along the Atlantic coast from Mauritania to Guinea. In 31 samples with a total of 8956 otoliths we identified 53 fish families, 75 genera and 101 species. Twelve fish families occurred in more than 2% of the samples. The families of Haemulidae, Mugilidae, Pristigasteridae and Sparidae were particularly numerous (found in 10.5–15.7% of samples). The most numerous species were Bigeye Grunt Brachydeuterus auritus (9.8%) and West African Ilisha Ilisha africana (13.3%). There were marked differences in the diets of terns from the Banc d'Arguin (Mauritania), The Langue de Barbarie (northern Senegal) and all more southerly sites together (Senegal, The Gambia, Guinea Bissau and Guinea). On Ile aux Oiseaux, Delta du Saloum, Senegal, we found long-term changes in the diet of the terns with a marked decrease in Brachydeuterus auritus and the family Sparidae and a strong increase in Ilisha africana. Our analyses suggest that breeding West African Crested Terns are food generalists rather than specialists. This is surprising in view of the general trend in terns of the genus Thalasseus. There are indications that chick diets may differ from those of adults. [ABSTRACT FROM AUTHOR]

West African Slender-billed Gulls Chroicocephalus genei are considered vulnerable due to a very restricted breeding range. However, little information on their ecology is available to support conservation action. We describe diet and foraging range of Slender-billed Gulls breeding in the Saloum Delta National Park in Senegal. Diet was analysed on the basis of fish otoliths in excretion (mixture of pellets and faeces) collected near nests at the end of the incubation period between 2000 and 2015. Gulls mainly consumed fish of the families Cichlidae (25–93%), Clupeidae (0–54%) and Mugilidae (0–34%). The log-ratio proportion of Mugilidae increased significantly between 2000 and 2015, but there was no significant trend for other prey taxa. In 2014, UvA-BiTS GPS-trackers were fitted to three Slender-billed Gulls to study movement and foraging range. During daytime, these gulls spent 27% of their time incubating the eggs, 10% elsewhere in the colony and 63% outside the colony on foraging trips. Foraging trips lasted on average 18 ± 9.5 (±SD) hours. Total distance covered was on average 96 ± 39 km with a maximum distance to the colony of 37 ± 13 km. There were marked and consistent individual differences in the flight paths of the gulls. In two birds, foraging mainly took place in mangrove-bordered lagoons, salt pans, creeks, rivers and a complex of abandoned rice fields. The third bird almost exclusively explored the Atlantic coast near a fishing village in The Gambia. The home range and the foraging area of the three birds together measured 2400 and 1800 km2, respectively. The diet components found near the nests of the three birds could only partly be related to their foraging areas. [ABSTRACT FROM AUTHOR]

A frequently used method to estimate diet composition is based on the identification of fish otoliths present in pellets and feces. However, whether pellets and feces provide similar unbiased estimates of the diet remains poorly understood. The diet of African Royal Terns (Thalasseus maximus albididorsalis) breeding in the Parc National du Delta du Saloum, Senegal, was studied. Prey species composition based on otoliths in freshly regurgitated pellets and a mixture of pellets and feces (excrement) accumulated near nests during the incubation period were compared. Altogether, 59 fish species were identified. Pellets contained far less prey species than excrement. Maximum diet overlap between excrement and pellets varied between 0.34 and 0.43 (mean = 0.36). Differences between minimum and maximum overlap between both sample types were small in all years. Pellets contained almost exclusively large otoliths (widths 3.0–8.5 mm), whereas excrement contained two fractions: large sized ones, identical to those present in the pellets and smaller-sized ones (0.5–3.0 mm) originating from feces. It is hypothesized that large otoliths cannot pass the intestinal tracts of the birds and are therefore regurgitated. Differences in prey species composition in pellets and excrement could potentially be explained by a combination of seasonal changes in availability of prey species and size of otoliths. Neither pellets nor feces alone give an unbiased picture of the diet of African Royal Terns. [ABSTRACT FROM AUTHOR]