The West African Crested Tern (Thalasseus albididorsalis) is the most abundant breeding tern in West Africa, nesting from Mauritania to Guinea. Its global population is estimated at less than 77,000 breeding pairs, mostly restricted to a few colonies in Senegal and Guinea-Bissau.
West African Crested Tern breeding in Bantambur, Guinea-Bissau by Teresa Catry
In this study, we tracked 20 birds, nesting in Bantambur, from late incubation to early chick-rearing, to characterise their foraging behaviour and to identify the most important sites for this population during the breeding period.
Terns foraged mostly in shallow waters along the coasts of Guinea-Bissau and Senegal. During single-day trips (i.e. no overnighting outside the colony) terns that stopped to rest took longer trips, travelled greater distances, and foraged further away from the colony.
Due to its recent split from the Royal Tern (Thalasseus maximus), the West African Crested Tern lacks a recognised conservation status, as well as a conservation action plan. Despite the recent efforts, which have resulted in the designation of Marine Important Bird and Biodiversity Areas (IBAs) along the West African coast, empirical data on critical sites for the West African Crested Tern is urgently required to evaluate the adequacy of IBA borders in support of the conservation of this species.
Bantambur, in Guinea-Bissau, is the second largest colony of the species, holding ca. 20,000 breeding pairs, which represents 25% of the global breeding population of the species.
Drone image of the Bantambur colony by Teresa Catry
We tracked 20 birds, nesting in Bantambur, from late incubation to early chick-rearing, to characterise their foraging behaviour and to identify the most important sites for this population during the breeding period.
Terns foraged mostly in shallow waters along the coasts of Guinea-Bissau and Senegal. During single-day trips (i.e. no overnighting outside the colony), terns that stopped to rest took longer trips, travelled greater distances, and foraged further away from the colony.
Terns spent the night away from the colony on 10% of all trips, and such overnight trips were significantly longer in duration, total distance travelled, and maximum distance from the colony. Therefore, overnight trips enhanced foraging further away from the colony, but also allowed birds to exploit a wider foraging area, by travelling overall longer distances.
Figure 5 from Correia et al. 2024: Important foraging areas and resting sites (circles) of West African Crested Terns breeding on Bantambur (diamond), Guinea-Bissau. The red line indicates the 95% used area of the colony.
Terns are considered visual predators foraging primarily during daylight hours. Nocturnal foraging seems, therefore, rare in this bird group. The tracked West African Crested Terns showed nocturnal flight activity on ca. 20% of all foraging trips, suggesting that nocturnal activity may be frequent in this species, and should be further confirmed and better understood in future tracking studies.
We show that the existing Marine IBA in Guinea-Bissau covers only half of the important foraging and resting areas used by the population of West African Crested Tern breeding on Bantambur, highlighting the importance of population-level studies for informing spatial conservation measures, as well as the need for national and international management efforts for the conservation of this species.
The important foraging and resting areas identified in our study may regularly hold up to 23.4% of the global breeding population of the West African Crested Tern, and, therefore, are relevant for the global persistence of the species, meeting the Criterion D1 for a Key Biodiversity Area (KBA) qualification.