Sunday, June 12, 2011

A fantastic calm and sunny day yesterday meant that we could get around the steep north and east sides of the island to continue the seabird monitoring. The gull colonies were first on our hit list, with Herring Gull chicks plentiful and easy to locate on the rocky outcrops. It became more of a challenge as we entered the Lesser Black-backed Gull colony as they tend to hide their chicks amongst the dense bracken and nettle beds. Lesser Black-backed Gulls form monogamous pairs and, although nesting colonially, defend their territory fiercely. It's important, therefore, that there is sufficient vegetative cover within each territory as exposed wandering chicks will often be pecked to death by neighbouring adults. Parent birds have a series of key-calls that act as commands to their chicks. A 'Kaw' call causes the chick to run and hide in cover, whereas a 'Mew' call summons the chick to come out and feed and a 'Kowp' call summons the chick to return to the nest to be brooded.

This Lesser Black-backed Gull has just finished an exhausting hatching session. It will initially take food from inside its parents' bill by pecking at the red bill-spot, but when older it will usually eat food off the ground when brought in by parent birds. (c) Richard Brown

Where Herring Gull and Lesser Black-backed Gull colonies overlap it can be difficult to differentiate between young chicks of the two species due to their similar size and almost identical downy patterning. A chick only a few days old (above) cannot be accurately identified until it's primaries have started to grow (below). A Herring Gull at this stage would show pale inner primaries, a key feature when separating fledged juveniles in flight. (c) Richard Brown

We continued on our gull-fest with perhaps the most docile of gull species. The adults are fantastic in the hand and upon release return immediately to their nest ledges. Kittiwakes begin nesting much later than Lesser Black-backed Gulls so it will be a couple of weeks before we can get in to ring the chicks. 
(c) Richard Brown

 Razorbills and Guillemots nest together in the boulder fields of the East Side and the chicks are often to be found side by side. They're easily identifiable, however, with Razorbills almost immediately showing the diagnostic white facial stripe of the adult. Guillemot chicks (above) have dark heads with paler flecks to the ends of their down whereas Razorbill chicks (below) have pale silvery heads. (c) Giselle Eagle

Razorbills fledge at only 18 days old while still flightless. Fledging usually occurs in the evening, when the adult bird leads the chick out of the boulders. Before this, the chick may have moved no more than 30cm away from its nest site. They call excitedly to each other, and the chick follows the parent bird (almost invariably the male) dropping down across boulders before eventually entering the sea. Once in the water the chick swims close to the side of the adult and together they swim silently out to sea. This chick, photographed only yesterday, will probably fledge this evening. (c) Richard Brown

Another update on the boys! Most of them have undergone their final moult before pupation. They've developed stunning white circles along their flanks, huge bright pink head surrounds with fake eyes, fantastically striped feet and their adapted legs have developed black spots (below), squirting out huge red warning streamers when under threat. Their moulted skins are left as a white papery deposit on the leaf on which they moult (above) and we have seen one of the lads eating the skin. (c) Richard Brown

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