Category Archives: 2019 Field Season

The Darkness of August

by George Divoky

Image Credit: Mike Morrison

While much has changed over the course of the 45 summers I have spent on Cooper Island, as warming from anthropogenic carbon emissions has modified the Arctic’s snow and ice habitats, one thing has remained constant. The sun is always above the horizon for 24 hours when I arrive in early June and it does not set until precisely August 2.

The importance and impact of that constant daylight is hard to overstate. When I arrive on the island I am not constrained by the day-night/light-dark cycle that I just left in Seattle, and I can work on whatever schedule I like while setting up camp and conducting initial colony censuses. Equally important is the high serotonin level associated with the constant daylight, which increases the optimism one typically has when starting a field season at any latitude. That optimism is also amplified by seeing the guillemots, some of whom I have known for over two decades, initiate breeding.

After the sun sets in early August, “nighttime” for the following two weeks consists of an increasing twilight period until the third week of the month, when the sky becomes dark for the first time since before my arrival. The loss of daylight is the first clear signal that the summer is ending. Despite the major impact on fieldwork and my psychological state, I used to welcome the arrival of August darkness as it allowed the guillemots to complete their breeding season. Black Guillemot young fledge under the cover of darkness. After 35 days in a nest cavity, the chicks depart the colony independent of their parents. They fly off at the darkest time of night and quickly move offshore to reduce the risk of predation by diurnal shoreline predators like gulls, jaegers or falcons.

A fully grown chick outside its nest case waiting for darkness to fledge

In recent years, however, the darkness of August has been a different experience for both the colony and for me. In the first two decades of the study, when the colony was almost three times its current size and breeding success was high, large numbers of nestlings would fledge every night. My dawn nest checks during those years found many just-vacated nesting cavities which provided daily evidence of that year’s breeding success and the promise that future breeding seasons would see large numbers of birds returning to their natal colony on Cooper Island.

However, the period of August darkness became quite different as the Arctic warmed. Starting in 2002, when annual summer sea ice melt notably increased, we began to see polar bears on Cooper Island. Polar bears on land are active during the nighttime hours and it was not uncommon to wake up in late August to find that bears had flipped over the wooden nest boxes and consumed guillemot chicks, sometimes wiping out half of the colony in one night. We addressed bear predation by replacing the wooden nest boxes with bear-proof plastic cases in 2012, but the continuing loss of ice that drives the bears to land each summer is also making the guillemots’ preferred ice-associated prey, Arctic cod, unavailable to parents for feeding their young.

In the 2019 breeding season that is just ending, decreased prey availability due to both a lack of sea ice and high sea water temperature underlie the death of 75 percent of the nestlings. While hatching success was good, only 25 percent of the 130 nestlings survived until late August. In past years when sea ice was just offshore and Arctic cod were abundant, over 75 percent of the nestlings would be expected to fledge. This year’s nestling mortality occurred mainly in late July and early August, when nearby ocean waters were so warm (up to 9 C or 48 F) that even the less preferred alternative prey, sculpin, were scarce. Guillemots typically have two-chick broods with the younger chick being fed less during periods of low prey abundance. This year none of the younger siblings survived past early August, the first year without bear predation that no pair was able to fledge two chicks.

The small number of surviving nestlings are now fledging. Having monitored them since they were eggs, including weighing them daily during the five-week nestling period, I have come to know them as individuals and am pleased when I open a nest case to find the surviving chick had left the previous night. But I am also aware that the extremely low breeding success this year, coupled with similar low success in the past two years, will cause the number of breeding pairs in the colony to continue to decline. Although the few chicks that have fledged in recent years can be expected to return to Cooper Island in two to three years, if they survive the ongoing loss of ice in their winter habitat in the Bering Sea, realistically the Cooper Island colony of Black Guillemots can never be expected to regain its past numbers nor its past success.

In earlier years both the bright start of a field season, as birds laid their eggs, and the darkness of late summer, when chicks would fly off into the night, could raise one’s spirits. This year, the darkness of August has been a period of melancholy and uncertainty of how long the colony might persist.

Loss of Sea Ice Takes Its Toll on Seabirds

By George Divoky

Pierre-Loup Jan, Katie Morrison, George Divoky, and Maria Coryell-Martin monitoring changes to the colony in August 2019 on Cooper Island.

The positive signs of colony size and breeding effort of the Black Guillemots on Cooper Island in June were too good to last.

After very high hatching success, the decreased ice and increased water temperatures took their toll as parents were unable to find prey in the warm, ice-free waters. Rapidly shifting ocean temperatures provided some days of good growth, but currently only one third of chicks are still alive. As the mortality was unfolding, we shared it with a reporter from the Washington Post for an article describing the impacts of climate change in Alaska in 2019.

The author notes that, “The early retreat of sea ice from the Bering and Chukchi seas has led to a jump in sea surface temperatures, altering weather patterns and upending the lives of residents who typically depend on the ice cover for hunting and fishing. It’s also affecting native species, including seals and seabirds.” They go on to quote me describing the high rate of chick mortality from the loss of sea ice, which limits guillemots’ access to their preferred prey, Arctic cod.

Read the full post at Proteus.

Birds on Nests During Incubation

By George Divoky

The Black Guillemots on Cooper Island continued to show signs of a turnaround from the poor breeding season of 2018 as egg laying and incubations has occurred in over 75 nests this year, compared to only 25 last year.  The breeding population saw the recruitment of 20 birds that had fledged from the island in past years but had yet to breed.  This is important since it shows that even with the decreased reproductive success and poor ice conditions of recent years, some birds are surviving to breeding age (typically 3-years of age) and returning to their natal colony, Cooper Island.  A major surprise was the return of a bird that fledged from the colony in 2012 and had not been seen since.

Unlike last year when daily nest checks found recently laid eggs being abandoned by parents, this year has found all eggs being regularly incubated.  Incubation is the least energetically demanding stage of breeding as the parent birds, which both incubate, take shifts of approximately 12 hours each day, having the remainder of the day to forage for fish.  Last year’s large-scale desertion of nests with eggs indicated birds were either starting incubation in poor condition or encountering low availability of prey during incubation.  Discovering the potential reasons for the differences between the last two years will have to wait until the fall when I have internet access to environmental data.  

While our daily nest checks have provided hope for high hatching success this year, other observations while we walk around the colony are causes for concern.  Most noticeable is the almost complete lack of guillemots sitting outside near nest sites or at the edge of the pond in the center of the colony, where guillemots have typically roosted when not incubating eggs or feeding young.  The daily period of colony attendance, approximately midnight to noon, used to have birds throughout the colony, while this year we see only the occasional lone bird or nonbreeding pair.  There is little visual evidence that the island supports a colony of over 150 birds.   Additionally, in early July we experienced a rapid disappearance of sea ice with the island being nearly surrounded by ice to no ice in sight in 2-3 days.  Both of these factors suggest that, despite the positive indicators seen in breeding effort and nest attendance, there are reasons to be concerned about the upcoming period of nestling growth and survival.

Read more coverage and field reports at www.proteusscicomm.org