Category Archives: Nesting

Trying to stay optimistic in a seabird colony that is half full – when it is really half empty

The standard and far-too-simplistic “test” of whether someone is an optimist or a pessimist is to ask if they consider half a glass of water to be half full or half empty.  The major flaw in the test is that it implies a steady state situation.  If the glass is being filled with water, one has reason to be optimistic about half a glass. If it is being drained, there is reason for pessimism.  The increasing or decreasing trend of a resource needs to be considered in deciding whether to be optimistic or pessimistic about the currently observed conditions.

This summer the Black Guillemot colony on Cooper Island had 100 breeding pairs.  Guillemots do not breed in the thousands or tens of thousands, as do many seabirds, and a 100-pair colony is a rather large aggregation of these beautiful birds. Anyone familiar with breeding guillemots who happened to visit Cooper Island this summer would likely be impressed with the 200 individuals breeding here.

However, it would be hard for anyone familiar with the history of the Cooper colony to be optimistic about its future.  Starting in 1975, we modified wooden boxes, floorboards and other debris on the island to create 200 nest cavities by the early 1980s. Guillemots quickly occupied the nest sites and the breeding population increased from 18 pairs in 1975 to just over 200 pairs in 1989 (graph below) when all potential nest cavities in the Cooper colony were occupied by breeding pairs.  

pairs and sea ice

This year, 2016, there are still 200 nest cavities.  The guillemots now nest in polar bear-proof Nanuk plastic cases that replaced each of the more vulnerable wooden sites in 2011.  The birds took to the new cases immediately, parent birds and nestlings clearly feel more secure in them and loss of nestlings to polar bears is now near zero – but this year half of the available nest cases are empty and no guillemots are breeding there.

We are currently examining the specific reasons for the colony’s decline to half of what it was in 1989 in collaboration with avian demographers but it is appears to be due to the guillemot subspecies on Cooper Island being one the few ice-obligate seabirds in the Arctic.  In a rapidly warming world the Arctic is the region that is warming most rapidly with dramatic and clearly visible effect on the region’s snow and ice habitats.  The decline in the Cooper Island colony started in 1990, the same year that warming temperatures in the region allowed the island’s guillemots to begin laying eggs earlier (as discussed in a previous post [link to last post]) and the decreasing trend in annual summer sea ice extent began.  Decreased summer sea ice has reduced the availability of the guillemots’ preferred prey, arctic cod, resulting in lower breeding success on Cooper Island and likely other colonies and, in this century, has increased polar bear presence on the island – which until we provided nest cases greatly reduced breeding success.

Given the loss of Arctic sea ice, it is not surprising that the Black Guillemots have also declined.  When the Cooper Island colony was near 200 pairs in the late 1980s, the annual minimum extent of sea ice in September averaged over 7 million square kilometers. As the guillemot population was declining in the last decade to its current 100 pairs, September sea ice extent has dropped as low as 3.6 million square kilometers – nearly half what it was when the Cooper Island study began.  In short, both Arctic summer sea ice and the Cooper Island guillemot colony have been reduced by half in the last quarter century.  

The future trajectory of summer sea ice seems clear.  Continued carbon emissions will cause continued warming, which will cause continued ice loss. All climate models project continued decline and eventual disappearance of Arctic sea ice if carbon emissions are not greatly reduced (graph below).  The path of the Cooper Island guillemot population, however, is less certain.  Like all animal populations the birds currently breeding on Cooper Island may possess sufficient behavioral plasticity to adapt and evolve to accommodate new conditions, just as their ancestors may have possessed when they adapted to exploit ice-covered waters.  Some guillemots may be able to survive and even prosper in an Arctic without summer sea ice – which, unlike the animals that have come to depend on it (including not only the Cooper guillemots but arctic cod, walruses, seals, and polar bears), cannot adapt and somehow stay frozen at temperatures above freezing.  

Observations of Northern Hemisphere minimum September sea ice extent (yellow line), and time series of global climate model projections (5 year running mean) and uncertainty (shading) for scenarios RCP2.6 (blue) and RCP8.5 (red). Black (grey shading) is the modelled historical simulation using historical reconstructed forcings. The RCP8.5 emissions scenario depicts a future where current rates of emissions continue unabated throughout the century, and the RCP2.6 scenario depicts a future in which the aims of the Paris Agreement are fulfilled.

Figure was adapted from the IPCC Summary for Policy Makers, 2013, Figure SPM.7b (

My days on Cooper Island in August are consumed with weighing nestlings.  Regular contact with the young of any species is bound to make one feel optimistic – it is still a wonder to me how quickly chicks grow from little balls of fluffy black down into gawky “teenagers” preparing to fledge into the Arctic Ocean, unaccompanied by their parents.  But as I walk through the colony seeing only open ocean to the horizon – where in decades past I saw large expanses of sea ice – I have to wonder how many young will survive to breed, and what conditions they may encounter should they return to Cooper to nest at sites we have been monitoring during the recent decades of rapid warming and plan to monitor in the even warmer future.

Early August has brought the first pulse of polar bears to Cooper Island, stranded here as their sea ice habitat that provides them a platform to walk on and hunt seals from is rapidly disappearing to the north. The bears, some of whom sleep for days on the island after swimming an unknown distance from melting sea ice, remind me that an entire biological community is being impacted by this halving, and eventual disappearance, of summer sea ice.  However optimistic I may feel about Black Guillemots’ ability to adapt to ice loss, I am aware I am observing the loss of one of the world’s most unique ecosystems.

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The Earliest Year

During the 1970s, in my first years in Arctic Alaska, people would talk about it being a “late year” or “early year” when discussing the timing of snowmelt, arrival of birds, flowering of plants, or the melting of sea ice. It was generally assumed one would rarely or ever see an “average year” but that over time annual variation would produce approximately equal numbers of late and early years with no reason to believe there would be any long-term trend to earlier or later years during the course of one’s lifetime.

That proved to be true for the first fifteen years monitoring the timing of breeding of Cooper Island’s Black Guillemot colony. One of the best ways of measuring the timing of breeding in a seabird colony is to obtain the median date of egg laying – the date when half of the breeding females in the colony have started to lay eggs.Corrected median date of egg laying

From 1975 to 1989 the median egg was laid in late June or early July. However, in 1990 the consistency of the previous 15 years was broken as egg laying occurred approximately one week earlier than in previous years. The start of the breeding season for the Black Guillemots on Cooper Island is related to the timing of snow melt because winter snow blocks the entrances to the ground level nest cavities and females need access to a nest before they will begin to form eggs. The shift in timing of breeding beginning in 1990 reflected a change in regional atmospheric circulation (the Arctic Oscillation) that resulted in warmer spring temperatures, earlier snow melt and earlier egg laying.

While the early breeding in 1990 was a major surprise at the time, what was almost more surprising was that the it was followed by a quarter century with no trend in the timing of egg laying at all – just an approximately equal numbers of early and late years, centered around a new average.

It is the two periods of relative stability (1975-1989 and 1990-2014) in the guillemot’s timing of breeding that make the findings on Cooper Island in 2015 and 2016 all the more intriguing. Last year’s 2015 field season saw the median date of egg laying occur on June 19, three days earlier than the previous early record and 6 days earlier than the 1990-2014 average. The early 2015 season followed record warm spring temperatures recorded at NOAA’s Observatory 20 miles away in Barrow.

This year things were again warm in Barrow with snowmelt at NOAA’s observatory the earliest on record and I assumed it would again be an early year on Cooper Island. But I was surprised at just how early it has been, with the median date of egg laying occurring on June 16, three days earlier than last year and more than two weeks earlier than the timing of egg laying when the study started in the late 1970s. 

Early egg laying is typically considered a good thing for Arctic birds, as it provides more time for raising young before fall migration. For the Black Guillemots, however, the warmth that has been melting snow and allowing earlier breeding has also been melting the sea ice in the adjacent Arctic Ocean. Black Guillemots in the Arctic are adapted to feeding in the cold waters around the sea ice where they can find their preferred prey, Arctic Cod. For the last 15 years, loss of sea ice in late July and August, when parents are feeding their young on Cooper Island, has caused a lack of food resulting in lower fledging weights, higher nestling mortality, and overall decreased nesting success. Black Guillemot chicks are just beginning to hatch now (mid-July) and will remain in the nest for the next five to six weeks. The ice-associated prey available to their parents may be again limited this year as the sea ice melt has been on a near record pace and a recent satellite image shows most of the waters used by Cooper Island’s guillemots are already free of ice.


All species and ecosystem processes in the Arctic have annual cycles tied to the timing of spring snow melt, which is trending earlier due to climate warming. The 42-year data set on the timing of Black Guillemot breeding on Cooper Island provides unique insights into the biological consequences of the well-documented physical changes occurring in the Arctic. Unfortunately there are very few multi-decadal data sets documenting the changes that have occurred to Arctic species, and that paucity of data makes the study on Cooper Island’s Black Guillemots all the more important to preserve and continue.


The Cooper Island study is maintained by donations to our nonprofit, Friends of Cooper Island, a 501(c)3.  Your donation will help us continue to monitor a warming Arctic. 

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Earliest breeding season in 42 years

The record setting snowmelt in Barrow this spring has resulted in the earliest breeding season for the Black Guillemots on Cooper Island in the 42 years the colony has been studied.

Median date of egg laying (when 50 percent of the nests have eggs) was June 16th. Three days earlier than the previous record – set in 2015. Early breeding is important this summer as birds may be able to have their young fledge before the major loss of sea ice predicted for August.

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