Analyzing Pellets and Feces of African Royal Terns (<i>Thalasseus maximus albididorsalis</i>) Results in Different Estimates of Diet Composition

Veen, Jan; Dallmeijer, Hanneke; Damme, C.J.G. van; Leopold, M.F.; Veen, Thor

doi:10.1675/063.041.0309

Cited by 8 publications

(4 citation statements)

References 13 publications

(12 reference statements)

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“…However, the number of suitable breeding sites is limited. Along the West African coast between Mauritania and Guinea, only a small number of sites are suitable for breeding but they may hold very large numbers of breeding seabirds (Veen et al, 2004(Veen et al, , 2018a(Veen et al, , 2019. The main sites from north to south are Parc National du Banc d'Arguin, Parc National de la Langue de Barbarie, Parc National du Delta du Saloum, Bijol Islands (Tanji Bird Reserve), Réserve Ornithologique de Kalissaye, Bijagós Archipélago, Bantambur (near Jeta) and Iles Alcatraz and Naufrage (Fig.…”

Section: Study Area and Bird Speciesmentioning

confidence: 99%

“…While one of the parents breeds, the other is foraging or resting outside of the colony; the number of breeding pairs therefore corresponds directly to the number of identified individuals. In West Africa, a seabird monitoring project has been ongoing for over two decades (Veen et al, 2004(Veen et al, , 2018a(Veen et al, , 2019 in which a variety of counting methods have been employed in the main breeding areas. Several areas consist of large colonies where birds cannot realistically be individually counted and hence need to be estimated.…”

Section: Coastal Seabirds and Manual Countingmentioning

confidence: 99%

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21 000 birds in 4.5 h: efficient large‐scale seabird detection with machine learning

Kellenberger

Veen

Folmer³

et al. 2021

Remote Sens Ecol Conserv

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We address the task of automatically detecting and counting seabirds in unmanned aerial vehicle (UAV) imagery using deep convolutional neural networks (CNNs). Our study area, the coast of West Africa, harbours significant breeding colonies of terns and gulls, which as top predators in the food web function as important bioindicators for the health of the marine ecosystem. Surveys to estimate breeding numbers have hitherto been carried out on foot, which is tedious, imprecise and causes disturbance. By using UAVs and CNNs that allow localizing tens of thousands of birds automatically, we show that all three limitations can be addressed elegantly. As we employ a lightweight CNN architecture and incorporate prior knowledge about the spatial distribution of birds within the colonies, we were able to reduce the number of bird annotations required for CNN training to just 200 examples per class. Our model obtains good accuracy for the most abundant species of royal terns (90% precision at 90% recall), but is less accurate for the rarer Caspian terns and gull species (60% precision at 68% recall, respectively 20% precision at 88% recall), which amounts to around 7% of all individuals present. In sum, our results show that we can detect and classify the majority of 21 000 birds in just 4.5 h, start to finish, as opposed to about 3 weeks of tediously identifying and labelling all birds by hand.

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Section: Study Area and Bird Speciesmentioning

confidence: 99%

Section: Coastal Seabirds and Manual Countingmentioning

confidence: 99%

21 000 birds in 4.5 h: efficient large‐scale seabird detection with machine learning

Kellenberger

Veen

Folmer³

et al. 2021

Remote Sens Ecol Conserv

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“…Because small and fragile otoliths may be more difficult to find than large ones, a possible bias is introduced due to underrepresentation of small fish. Furthermore, Veen et al (2018a) showed that small otoliths are strongly underrepresented in regurgitated pellets as compared to the faeces. The terns produce regurgitated pellets and defecate while sitting on the nest.…”

Section: Diet Analysismentioning

confidence: 99%

“…This study focuses on the diet of the West African Crested Tern Thalasseus albididorsalis (from here on WA Crested Tern) which was previously a subspecies of the Royal Tern T. maximus albididorsalis , but which has recently been given full species status based on DNA analysis (Collinson et al 2017). So far WA Crested Terns have received little attention in the literature (but see Veen et al 2003, 2018a,b, Correia et al 2019).…”

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confidence: 99%

The Diet of the West African Crested Tern Unveiled by an Analysis of Otoliths Collected Over 20 Years along Its Main Breeding Sites

Veen¹,

Dallmeijer²,

Diop³

et al. 2023

Ardea

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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.

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Foraging movements and important sites for conservation of the West African Crested Tern Thalasseus albididorsalis breeding in Guinea-Bissau

Correia,

Beal,

Gomes

et al. 2023

Mar Biol

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Assessing at-sea distributions and behaviour of seabirds to identify critical foraging sites and spatial overlap with potential threats is a major step for delineating conservation guidelines. The West African Crested Tern (Thalasseus albididorsalis) is the most abundant breeding tern in West Africa, nesting from Mauritania to Guinea. Its restricted breeding range and exclusive nesting at coastal low-lying areas, place this species at particular risk of losing suitable breeding and resting sites as a consequence of current global changes, namely, sea-level rise. The at-sea distribution of this species is mostly unknown, and therefore, the specific threats faced are still unidentified. Here, we characterize the foraging behaviour and distribution of West African Crested terns breeding at the world’s second-largest colony of the species, in Guinea-Bissau, by tracking 20 individuals. Overall, terns took an average of 2 trips per day, travelling on average 100 km per trip, but often reaching areas up to 120 km from the colony. Shallow waters, usually not exceeding 10 m in depth, and upwelling areas were mostly used as foraging sites. Nocturnal movements, rarely reported on terns, suggest active foraging at night. Key foraging and resting sites were identified, which altogether may regularly hold 2.5–23% of the global breeding population of the West African Crested Tern. These areas are only partly (ca. 50%) covered by the existing marine Important Bird and Biodiversity Area (IBA). Therefore, our results should be considered in any re-evaluation of the IBA borders.

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Analyzing Pellets and Feces of African Royal Terns (Thalasseus maximus albididorsalis) Results in Different Estimates of Diet Composition

Cited by 8 publications

References 13 publications

21 000 birds in 4.5 h: efficient large‐scale seabird detection with machine learning

21 000 birds in 4.5 h: efficient large‐scale seabird detection with machine learning

The Diet of the West African Crested Tern Unveiled by an Analysis of Otoliths Collected Over 20 Years along Its Main Breeding Sites

Foraging movements and important sites for conservation of the West African Crested Tern Thalasseus albididorsalis breeding in Guinea-Bissau

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