It Takes a Colony to Raise one Young

Cooper Island, Alaska, Aug. 27, 2009 — What seems like a long,long time ago,black guillemots on Cooper Island had the best of all possible worlds. The summer snow-free period was increasing annually, providing breeding birds with more time to raise their young, and the Arctic pack ice was close enough offshore that there was a readily accessible supply of Arctic cod to feed the nestlings. The only real dark cloud on the horizon was the realization, slow in coming over the past three decades, that the warming planet that had given the guillemots their “salad days” in the 1970s and 1980s could cause increasing melt of the pack ice, making Arctic cod less accessible and causing problems for parent guillemots provisioning their young in August and early September.

Even as the ice kept retreating during the 1990s there were reasons to think the guillemots could cope with the change in prey type and availability since even though this subspecies has specialized on prey associated with Arctic pack ice, the genus to which it belongs, Cepphus, is highly adaptable and lives on a wide variety of near shore prey in temperate and subarctic waters. It appeared that documenting how the Cooper Island guillemot population, with its many color-banded individuals, responded to an ice-free nestling period was going to be a rare chance to watch adaptation and selection in a wild population.

But this past summer suggests that the geographic shift in the guillemots’ prey may not be the deciding factor in the future of the colony, but the shift in two species that were uncommon in the area when the study began: the horned puffin and polar bear. The preliminary results from this summer show that hatching success (the number of eggs that hatched) was reasonably high at about 70 percent — but could have been over 80 percent had eggs not been displaced and broken by horned puffins pushing the eggs out of nest depressions and polar bears breaking the eggs by moving nest sites. Still, with over 180 guillemot chicks in nests in late July and early August, there was a good chance the colony could produce a sizable number of fledglings this year.

However,as August progressed the activities of puffins changed and visits by bears increased so that the number of guillemot chicks rapidly decreased to 100, and then to four chicks on August 16. While a few chicks died from lack of food or natural causes, the vast majority were the victims of puffins prospecting nest cavities and polar bears looking for food, with puffins killing (but not eating) about 80 chicks and polar bears killing (and sometimes eating) about 90. It is telling that the polar bear, an Arctic species forced south because of melting ice, and the horned puffin, a subarctic species moving north because of melting ice, could together cause the major breeding failure guillemots experienced this summer. While either species could have, by itself, greatly deceased breeding success, the combination proved devastating to the Cooper Island colony in 2009. A number of guillemot nests with two nestlings had young lost to both bears and puffins.

When I left the island late on August 17, one young guillemot had just fledged and there were three young still in nest sites, each with about two weeks to go before nest departure. It is likely that polar bear visits increased in frequency and duration after my departure, greatly decreasing the chances the three remaining chicks would successfully fledge.

Based on the frequency and activities of polar bears on Cooper Island in the last three years it appears likely that bears stranded on the beach looking for food will continue to cause major decreases in breeding success in the future. Surprisingly, it appears that non-breeding horned puffins, looking for nesting cavities and competing with guillemots for those cavities, could have an almost comparable impact on breeding success. Since the presence of both bears and puffins is related to the decrease in the ice extent and since there is no indication that the decrease in summer ice extent will reverse itself in the near future, both bear and puffin numbers on Cooper Island will likely increase in future breeding seasons.

Although the marine waters adjacent to Cooper are becoming more amenable to puffins, the establishment of a puffin colony on Cooper in the long-term will be prevented by the presence of polar bears that in recent years have preyed on puffin nestlings.

In the past week colleagues in Barrow and friends in Seattle have asked what the future of the guillemot colony is given this year’s observations. The short-term outlook is that breeding adults, with their high fidelity to nest sites, will continue to return to the colony even though breeding is likely to fail in most years because of bears and puffins. This lack of productivity will mean that, without immigration from other colonies, there will be no birds reaching breeding age and recruiting into the population. With overwinter mortality of breeding birds at approximately 15 percent and if no recruitment occurs, the colony will decrease in size by approximately 15 percent every year. This would mean that in 2025 the colony would be back down to ten pairs of guillemots, the same size it was in 1972 when I found it -– allowing me to exit saying “this is where I came in”.

Of course this assumes that the nest sites the bears destroy every year will be reconstructed to provide a nesting cavity and that some other factor doesn’t come into play. For instance, increasing erosion coupled with increasing storms and wave height may result in nest sites being washed away by late summer and fall storms.

While this assessment sounds gloomy it is also realistic, since the annual trend in summer ice extent leaves little doubt that there will be an ice-free Arctic sometime in this century. The number of polar bears forced to use the edge of the Arctic Basin as summering habitat will increase, and Cooper Island is one of the more logical places for them to aggregate on the Alaskan coast. And horned puffins will likely continue to visit Cooper Island in small numbers, drawn by the increases in subarctic fish in the region and a lack of suitable nesting cavities in the region.

The only way to know what will happen, of course, is to visit Cooper Island. And given this scenario, it is important to recognize the one certain fledge from the colony this year, since it may well be one of the last guillemots to fledge from the island. It survived a puffin visit that resulted in the death of its sibling and two bear visits that repositioned and almost destroyed the nest site where it was raised to fledging by its parents. If it can survive the next three years, it will likely return to Cooper Island for the 2012 breeding season. Even though the outlook for the colony is grim, seeing if that chick – the “Class of 2009” — does return will be enough to make me excited at the start of the field season three years from now.

I’ll have more thoughts on the field season, and the ongoing prospects for the colony, in the weeks to come. It looks to be a busy fall, with presentations as part of International Polar-Palooza, as well as places closer to home, and more analysis of the summer’s data and how it fits into the bigger picture on Cooper Island. Thanks to you who have followed the Cooper Island field season this summer. And special thanks to those who provided donations of moral,logistical and financial support allowing me to work on Cooper Island during this past field season. I plan to continue these posts here and on my website (cooperisland.org) in the off season and hope you visit during the coming months.

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