Friday, 15 July 2011

Laying down the foundations

Almost 70% of monitored nests are now occupied by a breeding pair. In 17 nests, the egg is being incubated in a nest-cup holding a temperature logger, so hopefully some valuable data on frequency of occurrence of egg neglect (breaks in incubation) are being recorded. One of these eggs has, however, been abandoned already and kicked out of the nest (see below). Another 10 nests have been occupied on a handful of occasions over the season, so there may be a few more pairs yet to lay an egg. It may seem late, but, last year, the last egg was recorded on 2nd August.

An abandoned egg, kicked out of the nest-cup. You can see a temperature logger (an 'i-button') in the centre of the photo for recording nest temperature to monitor egg neglect.

A handful of nests that fledged chicks last year have not been occupied at all during the day so far, leading me to assume that those birds are probably not going to breed this year. However, birds do not always occupy the nest during the daytime prior to laying, so there may be a few unexpected surprises yet. Daytime occupation of nests seems highly variable – typically, one or two birds might occupy the nest on two or three days over the course of maybe 3 weeks prior to laying. At one extreme, one or two birds of a pair were present on 8 occasions over the course of a month before laying an egg. Yet, other nests are checked every day and, day after day, recorded as ‘empty’, then all of a sudden, one day, I’ll find a bird sat there on an egg!

A pair of Storm Petrels occupying a nest-box during the day. This nest-box has not been used for breeding before, so these birds are probably young birds that may be about to breed for the first this space...

While Storm Petrels are still laying their eggs, most other seabirds are much further ahead in their breeding season. Of the few Shags (Phalocrocorax aristotelis), Guillemots (Uria aalge) and Razorbills (Alca torca) that have successfully bred this year, most of the young have fledged and left the cliffs. Gull (Larus spp.) chicks are almost fully-feathered (see below) and must be close to fledging. Related to the Storm Petrels, Fulmars (Fulmarus glacialis) also have a lengthy pre-natal development, but breed earlier than Storm Petrels. I’ve noticed the first few Fulmar chicks over the last week, but all still being brooded by a parent, so probably less only a week or two old; a tuft of pale grey downy fluff poking out from underneath an adult usually gives their presence away.

Great Black-backed Gull chick playing the ‘If I can’t see you, you can’t see me’ game

It was such a pleasant day on Mousa yesterday that I took my time ambling around the island, checking nests at a leisurely pace, and keeping my eyes open for anything of interest...I was praying for some Orcas to start leaping out of the flat-calm, shimmering, blue ocean. Passing through areas used by nesting Bonxies (or Great Skuas, Stercorarius skua), I was scanning the ground ahead for any fleeting glimpses of a chick scuffling away - the most I usually see of a Bonxie chick. However, today, I had close-up encounters with two chicks (belonging to different pairs), both of which were almost misfortunate enough to have my foot land on top of them! Frozen to the ground, not moving a muscle, and hunkered down in the long grass, I didn’t see either of them until I almost stepped on them. Each time, I stopped with a start and looked down to see a pair of large black eyes surrounded by golden fluffy down staring back up at me...
A Bonxie chick hunkered down in the long grass. It must be a few weeks’ old, as you can see a lot of the feathers growing in on the back and wings (though apologies for a bad photo taken on my phone!).