The Yelkouan shearwater is a medium-sized seabird that is endemic to the Mediterranean Sea, with between 300-500 breeding pairs in Croatia (BirdLife International, 2020).
They only come to land to breed on rocky islands and islets, like those found within the Lastovo Archipelago. They nest in natural holes, such as those in the cracks of rocks or between fallen boulders, occupying the deepest part available. This offers concealment from predators, as well as providing protection from the weather and helping to regulate the temperature.
The birds typically breed for the first time when they are 3-4 years old (Borg et al., 2010). The breeding cycle begins in November, when the birds start to visit the colonies (Bourgeois et al., 2008). During this time, known as ‘prospection’, the birds will prepare and defend their nests, and form bonds with their mates. They typically return to the same mate, and if they had previous breeding success, then they are likely to return to the same nest too (Bourgeois, Dromzée and Vidal, 2014). They usually arrive at the colony during this time early in the night, to reduce the risk of losing their nest or mate to intruders.
Mating begins in February, and pairs will meet regularly to court and mate. After this time, the females go on an extended foraging trip to acquire all the necessary nutrients required for egg production and laying (Mallory et al., 2008). When the females are away, the male will regularly return the nest to guard against intruders and prepare it for the return of the female (Gatt et al., 2019).
One white egg is laid in March (Bourgeois et al., 2008), with the male taking the first incubation shift whilst the female returns to sea to feed and regain her strength (Gatt et al., 2019). If the egg is lost to predation or otherwise broken, the female will not lay another. It is incubated for 50 days (Bourgeois, 2012), by both the male and female who take it in turns whilst the other goes foraging. During incubation, the foraging adult typically returns to the nest late at night under the cover of darkness, to prevent revealing the location to predators.
Hatching occurs between the end of April and beginning of May (Bourgeois et al., 2008), with the chicks resembling a grey ball of fluff. Both parents will feed the chick for a period lasting 60-68 days (Bourgeois, 2012). The adults can travel as far as 428km before returning to their chick to feed them regurgitated meals of small fish such as anchovies and sardines (Péron, 2013).
When the chick is big enough, the parents will reduce the number of return trips to feed them, and the chicks start to take trips outside of their nest. Eventually, the parents stop returning completely, and by July fledging of the chicks will begin (Bourgeois et al., 2008). Once all the chicks have fledged, the colonies are abandoned, with the birds returning to spend the non-breeding season at sea until the cycle starts again in November.
References:
- BirdLife International (2020) Species factsheet: Puffinus yelkouan.
- Borg, J.J., Raine, H., Raine, A.F. and Barbara, N. (2010) Protecting Malta’s wind chaser: The EU LIFE Yelkouan Shearwater project report.
- Bourgeois, K. and Vidal, E. (2007) Yelkouan shearwater nest-cavity selection and breeding success. Comptes Rendus Biologies, volume 330 (3), pages 205–214.
- Bourgeois K., Dromzée S., Vidal E. and Legrand J. (2008). Yelkouan shearwater Puffinus yelkouan presence and behaviour at colonies: not only a moonlight question. Comptes Rendus Biologies, volume 331 (1), pages 88-97.
- Bourgeois, K. (2012) Yelkouan Shearwater Puffinus Yelkouan, Updated state of knowledge and conservation of the nesting populations of the Small Mediterranean Islands, Initiative PIM.
- Bourgeois, K., Dromzée S. and Vidal E. (2014) Relationships between nest-cavity and mate selection, reproductive performance and fidelity in the Mediterranean endemic Yelkouan shearwater Puffinus yelkouan. Acta Ornithologica, volume 49 (1), pages 9-22.
- Gatt, M.C., Lago, P., Austad, M., Bonnet-Lebrun, A-S. and Metzger, B.J. (2019) Journal of Ornithology, volume 160 (3), pages 625-632.
- Mallory, M.L, Forbes, M.R, Ankney, C.D. and Alisauskas, R.T. (2008) Nutrient dynamics and constraints on the pre-laying exodus of High Arctic Northern Fulmars. Aquatic Biology, volume 4, pages 211–223.
- Péron, C., Grémillet, D., Prudor, A., Pettex, E., Saraux, C., Soriano-Redondo, A., Authier, M. and Fort, J. (2013) Importance of coastal Marine Protected Areas for the conservation of pelagic seabirds: The case of vulnerable yelkouan shearwaters in the Mediterranean Sea. Biological Conservation, volume 168, pages 210-221.
