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Read by Dave and Charley

Once they have fledged it will take a number of years for the juvenile seabirds to mature. For puffins and gannets it takes 5 years for them to reach sexual maturity but what they do in the intervening time is very different. Puffins will migrate out into the Atlantic Ocean, not seeing land again for at least 3, often 4-5, years. On the other hand gannets will migrate south for the winter but return to the nesting grounds every year, even though they are juveniles and do not breed. Identifying which gannets are juveniles, and therefore non-breeders, is actually quite simple due to their plumage. The more dark feathers they have the younger they are.

The gannet second from the right still has many black feathers in its wings, it is 2-3 years old

The gannet second from the right still has many black feathers in its wings, it is 2-3 years old

Whilst gannets can return to breeding grounds every year of their juvenile stage, puffin will not do so until they are at least 3 years old. When they do come back for the first time though, they come back late. Instead of arriving in March, like the breeding adults, they arrive in June boosting the numbers we can see in rafts on the water.

Large puffin raft

Large puffin raft

Seabirds not only migrate when they are juveniles but will do so in every year of their adult life. Leaving the breeding areas for other regions and the reasons they have for doing so depend on the species. Gannets, shags and gulls all migrate further south where the weather is warmer during the winter and where food sources are richer at that time of year. But they will all stay close to land if that is where the food and weather is best.

Gulls on migration in the Algarve, Portugal

Gulls on migration in the Algarve, Portugal

Puffins however may go further south but will not go anywhere near land. They do this because they are much more comfortable swimming than they are on land or even flying. They also do it because it is easier for them to avoid predators in the open ocean, where they can fly away, dive in to the water and remain in large groups to confuse predators. Staying in open water is also better for puffins to find food during the winter.

Puffins carrying sandeels on open water

Puffins carrying sandeels on open water

ECOLOGIST'S UPDATE

Between 30th May and 1st June Vicky and I were joined on Burhou by a gull expert from Guernsey called Paul Veron. We had two aims: catch and ring lesser black-backed gulls and count all gull nests on the island. On Thursday I will tell you about the ringing, but today is about the count.

Counting nests is a simple method, move through the colony counting all the nests using pieces of dry pasta to mark nests already counted. However, despite Burhou being so small it took over 6 hours to cover the whole colony and locate every nest!

Gulls mobbing Tim and Vicky whilst they count nests

Gulls mobbing Tim and Vicky whilst they count nests

We do the count at this time of year as we have to do it before the vegetation grows too much around the nests and obscures our view. We also do it whilst most nests will have eggs and are therefore easier to check they are actively being used - once chicks have hatched they wander away from the nest, the first few were hatching on this trip.

The first chicks were beginning to hatch - note the pasta locating a counted nest

The first chicks were beginning to hatch - note the pasta locating a counted nest

In total we counted 1,430 nests of gulls, containing over 3,000 eggs between them!! 6 nests were great black-backed gulls, 32 herring gulls and 1,392 lesser black-backed gulls. The lesser black-backed gulls are continuing to increase whilst the other two species are having a decent year so far, lets hope they breed well and successfully fledge their chicks as well. Of course the easiest nests to count were those just in front of the hut on Burhou!

A gull nest as seen from inside the hut on Burhou

A gull nest as seen from inside the hut on Burhou