Category Archives: 2018 Field Season

44th Cooper Island field season comes to an end

End of season field report by George Divoky.

For the past four decades, my field seasons on Cooper Island studying Black Guillemots have always begun with high spirits and a feeling of optimism. Experiencing the 24 hours of daylight in early June while documenting the return of individual birds to the island and their nest sites is always uplifting – some of these seabirds have been returning to Cooper Island for decades. Then, the days begin to shorten as nighttime returns to the Arctic. After monitoring the colony’s breeding activity for over three months, the end of the field season in late August lacks the intensity of the start of the season, but until recently, provided the gratification of having a large number of nestlings depart the island – with the hope many will return in the coming years.

The end of my 2018 fieldwork was as atypical and unpredictable as the first part of the season. In June I saw the colony had experienced a major decline in breeding pairs due to unprecedented high overwinter mortality of adult birds and many of the birds that did return failed to either lay eggs or incubate the eggs they did lay.

After those initial indications that many of the adults were in poor condition in late June, I was surprised to find that the chicks had high survival in late July and August – unlike the widespread nestling mortality witnessed in 2017. Last year’s low breeding success, with the younger of the two nestlings dying in almost all nests, was due to an early and major retreat of the pack ice in the Beaufort Sea, making the guillemots’ preferred prey of Arctic Cod unavailable to foraging parents. This past summer’s sea ice retreat was later than last year and atypical in that, although much of the Beaufort was free of ice by late August, a large remnant of sea ice remained near the Alaskan coast keeping the waters near Cooper Island cold enough for Arctic Cod.

A large remnant of sea ice helped keep Arctic Cod in the Black Guillemot’s foraging range this summer. Image Credit: Alaska Ocean Observing System

Our last two weeks on the island were busy. In addition to monitoring the growth and departure of the guillemot fledglings, we spent many hours capturing adult birds and outfitting them with light-sensitive geolocation and activity data loggers. The high mortality during the nonbreeding season of 2017-2018 shows that winter conditions affecting adult survival, rather than the success of the breeding season, may now play the major role in determining the fate of the Cooper Island colony. As part of the SENSEI project, we deployed over 30 data loggers on adults that will provide us with information on their movements, distribution and activities from this fall until they return to the Cooper Island colony next spring.

Light-sensitive geolocation and activity data loggers help us learn where the Black Guillemots go during the winter. Image Credit: George Divoky

My field assistants, Thomas Leicester and Mike Morrison, and I did see individual variation in the ability of the guillemot parents to find cod in the ice-free but cold (<4 degrees Celsius) foraging area. While some chicks weighed over 300 grams in their third week in the nest, some nests had young with large variation in daily growth and weights remaining in the low to mid 200 gram range. While it was heartening to see nearly 40 guillemot nestlings fledge this year, due to the number of nonbreeding pairs and those that abandoned eggs, chick production per active nest was well below the one fledging per nest needed to sustain a stable population.

While I typically use my first week after the field season to slowly transition into an off-island existence, as I adjust to a life with running water, internet access and no polar bears, this year I traveled to Great Britain for the International Seabird Group Conference in Liverpool. I have always felt a kinship with British seabird researchers as my initial interest in conducting a long-term seabird study came from reading the books of Ronald Lockley, who in the early 20th Century decided to live on an uninhabited British island where he could study seabirds.

After the conference I traveled to the Centre d’Etudes Biologiques de Chizé where I am collaborating with Christophe Barbraud and others who, as part of the SENSEI project, are analyzing the 44 years of demographic data obtained on Cooper Island.

In spite of the highs and lows of the past three months, I am glad to have completed another field season of our long-term study. The unexpected findings of this past summer show that our work has never been more important as we continue to monitor a rapidly changing Arctic. I look forward to 2019 and hope things improve for the Black Guillemot colony in the 45th year of our fieldwork.

The first chick of 2018 has fledged from Cooper Island!

In a breeding season and field season that has been a tough one for both the Black Guillemots on Cooper Island and the investigators studying them, today was a day of celebration as morning nest checks revealed that the oldest nestling on the island had departed for the sea during the night.

The first fledge of the year is always exciting since it is an important benchmark in our field season, which begins with recording the owners of nest sites and continues with observing the dates of egg laying and monitoring the hatching and subsequent growth of nestlings.  While it is the parent birds who get all of the credit for a successful nesting season, we cannot help but feel some satisfaction having monitored daily the details of their three-month reproductive cycle.  Additionally, and certainly now with the recent decline in the size of the colony, a fledged chick provides hope for the future.  With sufficient luck, in three years the chick that fledged last night will return to Cooper to join the breeding population.

So we congratulate the proud parents White-Black-Gray, a bird fledged from Cooper Island in 1995 who has bred here since 2000, and Blue-Blue-Yellow, an immigrant (likely from one of the large Russian colonies) who had been breeding on the island for the past twelve years.

We are hoping that in the next few days their now independent fledgling will be joined by its sibling and a good number of the 50 birds that remain in nest sites. 

Uncertain Future for Nestlings: Sea ice retreat shifts prey out of foraging range

George’s latest field report describes his daily nest checks as parents are feeding chicks to prepare them for fledging.

Arctic sea ice grows and shrinks during the year (seasonal cycle), reaching its annual minimum extent at the end of every summer (early-mid September). Currently, 2018’s sea ice extent is below the minimums from the 1980, 1990, and 2000 decadal averages. Image Credit: Zach Labe

Black Guillemots have their young remain in the nest for almost five weeks, being nearly adult weight and independent of the parents when fledging. Returning to the nest with a single fish in their bill is a breeding strategy found in all member of the genus Cepphus; it reflects the abundance and predictability of prey in the nearshore waters where parents forage while provisioning young.

For guillemots breeding in subarctic and temperate areas, where the nearshore provides a diverse and ample supply of forage fish, the strategy works well. In the Arctic, however, Mandt’s Black Guillemot has had to adapt to a different nearshore environment. Because of sea ice covering and scouring the nearshore much of the year, and the low productivity and biodiversity of the region’s marine waters, there is a typically a paucity of nearshore fish to feed their young.

The sea ice is central to supporting an ecosystem, with Arctic Cod being the primary forage fish, that can provide an abundant source of prey when the edge of the pack ice occupies the nearshore. Mandt’s Black Guillemot has been able to breed in the Arctic “nearshore” due to this presence of sea ice near their breeding colonies.

The strategy worked well as long the breeding colonies were adjacent to the Arctic pack ice and sea surface temperatures were low. These conditions were present for the first thirty years of the Cooper Island study and the growth and fledging rate of guillemot nestlings was high. Now, as summer sea ice retreats earlier and farther from the coast, nestlings and their parents could no longer count on having 35 days of high prey availability. This has resulted in decreased chick growth, increased mortality, and poor condition of those nestlings surviving to fledging.

This year, with ice visible north of the island until a few days ago, there was an abundance of Arctic Cod. A walk through the colony found many parents flying back to their nests with adult cod (some bigger than six inches). Chick weights and survival reflected this abundance with no mortality of nestlings yet being recorded this year.

However, since sea ice was blown offshore by strong south winds two days ago, most chicks have been losing weight with others having little or no growth. Based on what we have seen in past years, parent birds should soon be shifting their prey choice to the more predictable – but less preferred – sculpin. The abundance of sculpin – which are present in a range of water temperatures – and the parents’ ability to shift their foraging strategies will determine the fledging success of the nestlings this year.

One of the reasons nesting guillemots are such good monitors of prey availability in nearshore waters is the lengthy time parent birds have to provision their nestlings, as guillemot young stay in the nest for five weeks after hatching. During that time parent birds are foraging for most of each day and returning to the nest nearly once an hour with a fish.

The current conditions of diminished sea ice have us approaching our daily nest checks with far more uncertainty than we did in the first decades of our study – when we expected chicks to have a steady growth rate until fledging. In the next few weeks a nest case could contain nestlings in poor condition, signs of hunger-motivated sibling aggression on the younger chick, or a number of large sculpin uneaten by the nestlings due to the size of their spiny bony head.

The one bright spot in our nest checks this year has been site E-11 where the chicks hatched from the first eggs laid this June. These nestlings are extremely healthy having been raised on adult Arctic Cod by two highly experienced parents, both over 20 years of age. The oldest nestling is just two to three days from fledging and demonstrates the benefits of parents laying eggs as soon as spring snowmelt allows.