Egg season

Yes, full egg season is upon us. Rockabill is teeming with eggs. Some of our main species, Roseate (Sterna dougallii) and Common (Sterna hirundo) terns have now laid their second and third eggs, respectively. Arctic terns (Sterna paradisaea) and Black Guillemots (Cepphus grylle) are also on their way and Black-legged Kittiwakes (Rissa Tridactyla), have just started… we still see them traveling around for some algae as nesting material, but some eggs started popping out!

Common tern (Sterna hirundo) with a three-egg clutch during nest checks. Photo taken under NPWS licence.

 Common terns get extremely protective and aggressive during this period. We miss the days we could walk the island peacefully! Now we are being attacked left and right, they peck our heads, our hands, poop on our heads and let’s admit it, sometimes on our faces too and scream in our ears. You have to admire their courage! They will do everything to protect their potential offspring. As Tim Birkhead says: “eggs are the most beautiful thing” indeed! Females invest so much on them, all their nutrients in the prior weeks before laying, the energy during the incubation period (shared by both partners in this case) and in protecting them from predators. During the process of egg laying, males will feed females. It is a funny thing to watch males coming into the colony holding fish in their bills and trying to find their partners. When they do find them, they sometimes still seem to tease them a bit before they actually feed them. I can definitely identify with the “hangry” (hungry + angry) females annoyingly screaming until fed, and sometimes after too, begging for more! Common terns normally lay 3-egg clutches in open nests on the ground. Roseates, on the other hand, generally lay 2-egg clutches in the wooden nest boxes provided, but that’s not to say that some Roseates will not lay open nests or just have the nutrients or energy for a single egg. Reproduction is a serious investment in the life of a seabird. If a bird needs to prioritize its own body condition of if reproducing during that season does not look favourable, for external factors, a bird will likely skip a reproductive year and try again the following season.

Roseate terns (Sterna dougallii) can be seen incubating eggs inside nest boxes provided. Photo taken under NPWS licence.

During egg season, one of our main worries is to keep the island predator free. Luckily here on Rockabill, we do not have to worry about any rodents (they would probably keep me off the island too!), but we do need to worry about gulls and birds of prey, especially Great Black Backed gulls (Larus marinus) and Peregrine falcons (Falco peregrinus). If given a chance, they predate on nutritious eggs, and sometimes on adult birds too, leaving a trail of destruction. For that, we have a gull scarer device, which plays distressing calls to keep gulls away, and we also do 5 AM shifts, when we try to keep the colony patrolled and busy and scare any attackers with our presence :)

Roseate egg predated just outside the nest box, likely by a Great Black Backed gull (Larus marinus). Photo taken under NPWS licence.

We are hoping for a very productive season, with many fledglings successfully leaving us at the end.  For now though, you can find us counting eggs around, under the Irish sunshine, wearing the most exotic three-layer head attires :)

That busy dinner hour! Common terns (Sterna hirundo) enjoy the Rockabill sunset while waiting for that take away fish :) Photo taken under NPWS licence.

Until next time,

Heidi Acampora

& the Rockabill team