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Season's End

posted 5 Aug 2013, 07:32 by Philip Collins   [ updated 22 Aug 2013, 01:49 ]
A colour dyed Kittiwake with chicks.

The Puffin Island 2013 field season has come to an end. July 31st marked the last trip for this season, and unfortunately this date was determined ultimately by the complete breeding failure of the kittiwakes. All breeding pairs within our study plots (and a larger control plot) failed to fledge any chicks, with a large number failing even to lay eggs.

The Kittiwake control colony - The left hand image shows part of the colony early in the season, when there were numerous birds building nests. The right hand image shows the same part of the colony a week ago, completely deserted (Click images to expand) 

As I have mentioned numerous times before in this blog, the most obvious cause of this widespread failure is the abnormally cold spring (the coldest in 50 years). A reasonable explanation for the widespread failure is poor feeding conditions before breeding leaving the birds in a condition where they could not manage the energetic demands of raising young. This was evident through: the late arrival of adults to the colony, the failure of many of these birds to lay eggs, the failure of eggs to hatch, and the failure of chicks to fledge. By all accounts it seems that the kittiwakes on Puffin Island are not alone in having such a poor year, with other colonies throughout the British Isles experiencing very low productivity as well.

Although the poor spring conditions are a large factor in this year’s breeding failure, it is not solely accountable for all failures. It is normal for a proportion of birds to fail at breeding in any year; breeding is energetically demanding and birds face numerous pressures throughout the breeding season. We were lucky enough to capture one of these pressures on the time lapse cameras. As shown below, it turns out that a Peregrine Falcon was predating the few chicks that did hatch.

Peregrine predating kittiwake chicks (click to enhance) - The peregrine is highlighted by the white circle, a returning kittiwake is highlighted by the black circle. 

Interestingly it turns out that this particular bird was predating the chicks before sunrise. Perhaps it was taking advantage of the low light conditions to avoid mobbing behaviour of surrounding birds.  As disappointing as it was to have failure of chicks, capturing predation events like this on camera is certainly not common, and provides us with an interesting insight in to the hunting behaviour of the peregrine, as well as the predation pressures acting on the kittiwakes.

As doom and gloom as it all sounds, the field season has been very interesting and ultimately useful. The first season of fieldwork for my PhD coinciding with the worst kittiwake breeding season for over 30 years is by no means an outcome I would have hoped for, but it has proved eye opening nonetheless. Also it could be said that recording what happens in poor breeding years is of high importance as it helps us to develop a better understand of the way the birds respond to certain environmental pressures.

It should also not be overlooked that other species on the island seem to be doing well. Ringing trips by the SCAN ringing group ringed large numbers of Razorbill, Guillemot, Shag, Cormorant and gull chicks indicating that many of these species actually had a good year.

The guillemots seemed to do well this year, with many chicks such as the one shown above successfully fledging. 

So, a long few months of trawling through countless hours of time lapse photos, and battling with other data analysis now awaits me before I can get back out to the island next spring. Here’s hoping the time flies by. 

A completely unrelated image of a seal. Why not.