Category Archives: Black guillemot

2018 Census

In this week’s field report, George talks about specific birds as well as the overall report of his 2018 Black Guillemot census on Cooper Island.

Nature, when observed or monitored for any extended period, typically provides a predictability that is reassuring in its consistency and sufficient surprises to keep one engaged.

For over four decades, my first task after I set up camp was a census of the Cooper Island Black Guillemot colony. This year was an excellent example of this balance of the expected and unexpected.

Since the 1970s, the majority of the birds breeding in the colony have had, in addition to a numbered metal band, a unique combination of color bands allowing identification with binoculars of individual birds. My census of the colony consists of recording the number of occupied nest sites and the color band combinations of the individuals occupying each site. This allows me to determine the birds who survived the winter since last year’s breeding season and whether they have retained the same nest site and mate.

Colorful bands make it easy to identify familiar birds and newcomers (without bands). Image Credit: George Divoky

Black Guillemots, like most seabirds, have high annual survival of adult birds and high mate and nest-site fidelity. On average 90 percent of the individuals breeding on Cooper have returned the following year with mate and nest-site fidelity over 95 percent. With loss of breeding birds so uncommon and changes in mate and nest site so rare, past censuses consisted primarily of confirming last year’s pair was again occupying a particular nest site. For the small number of nests where one member of a pair did not return, there typically was a new recruit already occupying the vacancy by the time of my census–either a bird banded as a nestling on Cooper Island or an immigrant, indicated by its lack of any bands.

In the past, the high survivorship of breeding birds meant that some of the individuals I resighted each June were ones I had seen for over 20 years, and in many cases had known since I had weighed them daily as a nestling. The resightings of these individuals as adults provided an annual touchstone that was an important part of both my emotional and scientific connection to the colony.

My initial census of the colony this year was unlike any in the past. The loss of breeding birds over the winter was the highest on record. Nearly one-third of the 170 birds that bred in 2017 not returning to the colony in 2018.

As mentioned in an earlier post, many of the 50 pairs that had eggs this year (down from 85 in 2017 and 100 in 2016) consisted of widowed birds that both lost a mate over the winter. The decrease in breeding population was exacerbated by the paucity of previously nonbreeding birds present to recruit into the breeding population. Some established breeders widowed over the winter are the sole occupants of their nest sites. Even pairs that did survive the winter have shown much lower mate and site fidelity than I have observed in previous years.

The disturbingly high percentage of birds lost to overwinter mortality comes as a major surprise but a simple percentage fails to capture the full impact of what I experienced during this year’s census.

Many of the individual birds I have known for decades were among those absent from the colony. Most notable was Yellow-Gray- Green, a 21-year-old female banded as a chick in 1996 and breeding on Cooper since 2001. She was featured on the cover of last winter’s Audubon magazine. Another individual absent this year with an even longer history on the island is White-Gray-Blue, who fledged from Cooper in 1989 and bred on the island during 23 years of rapid environmental change including of decreases in sea ice, warming ocean temperatures, increased polar bear nest predation and major shifts in prey availability.

George’s “Cover Girl,” featured here on a December cover of Audubon Magazine, didn’t return to Cooper Island this year. Image Credit: Peter Mather for Audubon

While examining this year’s colony census at the level of the individual bird, versus a review of declining numbers is disheartening, it also provides some reasons for optimism–a rare feeling this field season.

My census found that a number of birds fledged from Cooper in recent years recruited into the breeding population this year, starting what I hope will be a long and productive career as breeders. These birds, and their young–the fledging chicks we hope they produce later this summer–provides one both with optimism and motivation to maintain the long-term study. As Hannah Waters pointed out in her excellent article in Audubon magazine, the guillemots are going to have to adapt and evolve for the colony to survive in a rapidly warming Arctic.

The hope that this year’s first-time breeders and their young will find a way to maintain the colony during the major changes occurring in the Arctic allows me to maintain a positive attitude as I continue to monitor this year’s breeding season.

Seabirds and Sea Ice

Over most of its range the Black Guillemot is a nearshore seabird, occupying coastal waters during both the breeding and nonbreeding seasons, as do other members of the genus Cepphus. Pelagic or open ocean waters can offer abundant prey resources, but these options are often distant, patchy and unpredictable.

The nearshore typically offers seabirds a smaller but more reliable source prey base consisting of forage fish and benthic fauna from the ocean floor such as crustaceans or mussels.

The Arctic Ocean has extensive sea ice cover in the nearshore for the majority of the year; this presents a number of challenges to a nearshore species. Our work on the Cooper Island Black Guillemots has revealed a number of ways in which the species has met these challenges.

The current view from my cabin window illustrates one of the major problems guillemots face in the Arctic. Sea ice extends from the north beach of the island to the horizon and covers Elson Lagoon to the south. The only water available to the guillemots is a brackish pond in the center of the colony that provides no prey but is deep enough to provide sanctuary if the guillemots need to dive when pursued by an owl or falcon — regular visitors to the island.

While guillemots arrived on the island almost a month ago and egg laying is now complete, until recently the closest predictable open water where guillemots could find prey was approximately 20 miles away, off Point Barrow where winds and currents shift the sea ice creating an area of open water. This opening is called a lead. The Cooper Island guillemots stage there in April and May before coming to the island. (Editor’s note: Leads are important for wildlife, because they allow for access to oxygen in the case of seals and walruses and prey in the case of seabirds; you can read more from the National Snow and Ice Data Center here.)

This distance between the Cooper Island guillemots’ nesting colony and access to their prey resources during egg laying and incubation is in sharp contrast to what guillemots breeding in subarctic or temperate waters find at their breeding colonies. These birds occupy waters directly adjacent to colonies well before egg laying and foraging areas may even be within sight of nests. The birds breeding on Cooper Island (and likely all colonies of Mandt’s Black Guillemot Cepphus grylle mandti, the high Arctic subspecies of Black Guillemot) have responded to this spatial disconnect by having a well-defined periodicity in their daily colony attendance. Every day, the parent not incubating eggs and all nonbreeding individuals vacate the colony from approximately noon until midnight. The birds fly individually or in small groups to open water where they can feed for almost half the day before returning to the colony just as the “midnight sun” is at its lowest point in the sky.

MODIS image from July 9; snow and ice have blue/cyan color, while clouds will be lighter gray/white. Image Credit: David Douglass/USGS

While it seems individual birds could fly offshore to open water to feed anytime during the day, there are a number of possible reasons the observed colony-wide pattern of attendance and abandonment developed. For the half of the day when the guillemots are absent – from approximately noon to midnight – there is no evidence that Cooper Island supports a colony of Black Guillemots. It appears to be just a barren sandbar that happens to inexplicably have 200 scattered black plastic cases along with a small cabin surrounded by a bear fence. Falcons, Snowy Owls, and other predators moving along the barrier islands would have little reason to be attracted to this place.

The timing of the birds’ departure and return may be related to changes in air temperature and its effect on ice formation. On nights when the air temperature is below freezing (as it was last night), I have frequently observed the formation of new ice on the surface of the few spaces of open water in the sea ice directly adjacent to shore. This newly formed ice melts in the morning as air temperatures rise. Nocturnal formation of new ice in the waters adjacent to the pack ice reduces the amount of open water available for guillemots to dive for the prey.

This temporary daily reduction in foraging area could be expected to have been pronounced during the Last Glacial Maximum when air temperatures were lower and the ancestors of the Cooper Island guillemots occupied an Arctic refugium. The current pattern of colony attendance for the Cooper Island colony – foraging during the warmest part of the day and attending the breeding colony at night – could have evolved as a way of maximizing the amount of open water available for guillemots.

The large expanse of shorefast ice north of the island this year is persisting later than expected compared to recent years. While the nearshore ice may now be forcing the Cooper Island guillemots to fly further in search of prey, it could benefit the colony later this summer should ice remain in the nearshore close to the colony. In recent years a lack of sea ice when the guillemots are feeding young resulted in increased nestling mortality as higher sea surface temperatures reduced the availability of Arctic Cod, the guillemots’ preferred prey.

Should this year’s nearshore ice break up slowly over the next month, Arctic Cod could remain in the guillemots’ foraging range and allow increased chick growth and fledging success. The latter is urgently needed for the colony to reduce its current population decline. First eggs will be hatching in about two weeks and our daily weighing of nestlings and prey observations should demonstrate how much this year’s persistent sea ice has affected the guillemots’ nearshore environment.

The First Egg!

The first egg of the 2018 breeding season was laid on June 24th by White-Black-Gray.  She fledged from Cooper Island in 1995 and has lived through a period of major climate change in the Arctic. Hoping she, and the other 150 guillemots in the colony, have a successful breeding season!

The somewhat bad news is that the Audubon cover girl is not back.  While I have not been able to ascertain survival for all nests, it appears that the percentage of birds returning will be similar to last year: 20 to 25 percent.  The high mortality again has surviving birds pairing with neighbors since there are almost no nonbreeding birds to recruit.  Colony size will likely drop but, again, the amount is unknown now.

I’m still working out camp logistics and hoping the rest of the snow is gone soon so I can finish setting up camp.

George’s “Cover Girl,” featured here on a December cover of Audubon Magazine, didn’t return to Cooper Island this year. Image Credit: Peter Mather for Audubon