In the annual cycle, Yelkouan Shearwaters are ‘early birds’ – they start visiting the colonies in winter. That is why the team started colony work in February to monitor their nesting. Peak of egg-laying is end of February and beginning of March.
At the colonies, Yelkouan Shearwaters are strictly nocturnal and working with these birds one has to be prepared for long night shifts. Even with moonlight the activity of the birds at the colony at night is lower and in moonlit nights less birds come in or leave. Few days after full moon, when the moonrise is in the evening, relatively short time after dusk, the shearwaters visit their colony during this narrow time slot and the air is vibrating by their wing beats and ghostly scream-like calls. These are the nights when we manage to handle many Yelkouans in a very short time. After the bright moon is up and illuminating the night sky, the colony falls silent. This adaptation of the birds to the moon phases is probably there in order to avoid predators during brighter nights.
Monitoring the Yelkouans in selected sea-caves from pre-egg laying to fledging we were very excited to get a first glance of a freshly hatched chick. But even at an older age Yelkouan Shearwaters chicks are really cute. In July, the last young fledge and the colonies are abandoned when adults and young fly into the Agean and Black Sea where they spend the non-breeding season.
Two Yelkouan Shearwater sub-colonies in Malta were visited regularly and during many night visits GPS units were attached to individual adult birds to track their at-sea movements. In March and April we even increased the number of nights at the colonies since this is the peak of the breeding season of the species and the GPS tags had to be retrieved.