Shedding some daylight on the winter range of black guillemots

SEATTLE, WASHINGTON — Declining daylight is a concern to many at this time of year as we turn our clocks back one hour and experience a stepwise decrease in late afternoon daylight while preparing for seven more weeks of increasing darkness. Day length in Seattle is now down to less than ten hours but is about twice what is being experienced by the guillemots that bred on (and, thanks to the new Nanuk nest cases, fledged from) Cooper Island this summer. The length of the guillemots’ days are on my mind this fall, and will be until next field season, because of an unexpected addition to the 2011 fieldwork that could be a major complement to what we know about Cooper Island guillemots.

Dr. Iain Stenhouse of the Biodiversity Research Institute, who has worked on arctic seabirds and now conducts research in Maine, contacted me in early August asking if I might be able to deploy six geolocators on the Cooper Island Black Guillemots. (BTW, for those only familiar with guillemots breeding in the nest boxes and cases on Cooper Island, this picture below of Iain’s study site in Maine, where guillemots breed in coastal rock rubble, demonstrates why the nest access on Cooper Island is so unique.)


Iain, Jennifer Goyette, and Lisa Eggert, of the Biodiversity Research (BRI) Institute looking for Maine guillemot nests on the coast of Maine. Credit: Jennifer Goyette

Geolocators are light-sensitive data loggers that measure and store data on the time of sunrise and sunset by day. The geolocators arrived on Cooper Island just as the nestling period was ending and we put them on six breeding adults using the same technique as Iain by attaching them to a plastic band of the sort used to color band individuals. Next spring after the birds are recaptured and the data downloaded, the daily latitude and longitude can be calculated using a process known as light-based geolocation. While not as accurate as systems that obtain a GPS position (accuracy for geolocators is in the region of +/-150 km) nor as handy as having a satellite transmitter, the geolocators can provide important information about migration routes, stopover areas and wintering locations — and for a rather reasonable cost per bird.


Close up of a geolocated on the leg of a black guillemot.

The data from the geolocators on our study birds should provide some interesting information on individuals that until now we only could monitor during their three months at the Cooper Island colony. We assume we know the general area where Cooper Island black guillemots winter — the pack ice of the Western Arctic.


Map showing the extent of the Western Arctic winter pack ice where black guillemots spend the winter months, but where exactly we don’t know. Red represents 80-100 percent ice cover and yellow represents marginal ice zone. Yellow pin shows the location of Cooper Island.

Having survived the Last Glacial Maximum (approximately 25 thousand years ago) in an unglaciated part of the Arctic Basin, they became year-round residents of the Arctic, living in recurring cracks and other open areas in the pack ice during the winter months. In winter guillemots have been seen and collected as far north as Point Barrow, where wind and currents maintain some persistent open water, while some go into the Bering Sea as far south as the Pribilof Islands. But we have no idea exactly where any of the individual guillemots from Cooper Island might winter.

One of the problems of using geolocators on species that winter near the latitude of Cooper Island is that the sun is below the horizon for about 65 days, so wintering areas might have to be inferred from late fall and early spring locations. While anything the geolocators can tell us will be interesting, the most intriguing data might come from the periods immediately prior to and after the breeding season. Black guillemots are found next to the sea ice in the Chukchi Sea in fall and the data currently being obtained by the data loggers will, when compared with satellite imagery of ice cover, allow us to see just how much ice formation affects late fall movements. Similarly, what guillemots do from March to May before their June arrival at the colony is a complete mystery. In April, guillemots are in the lead off Barrow in numbers, but when they arrive there and how they get there (i.e. in rapid or gradual movements) is unknown.


Cooper Island guillemots off Barrow having arrived from unknown wintering areas. Credit: Kate Stafford

We had an exciting time deploying the geolocators in early September as we captured six breeding guillemots still provisioning their young. Waiting for the parent birds to return with fish was made all the more exciting by the presence of a sleeping polar bear. Next spring will be even more exciting as we capture the tagged birds when they return to their nest sites. Assuming normal overwinter mortality at least five of the birds should return next June. After downloading the data, we will send it to Iain Stenhouse for analysis and determination of locations.

It is likely that geolocators will be used again on Cooper Island. Assuming the 2011-2012 results show the utility of the technology, there are a number of specific topics that can be investigated. Since the formation and decomposition of the pack ice shows a good amount of annual variation, it would be worthwhile examining fall and spring movements in relation to variation in ice conditions. Additionally, outfitting some individuals for more than one year could provide insights into fidelity to wintering areas. And as often happens once the technology starts to inform us about previously little known aspects of natural history, there is always the chance of a major surprise that could prove previous assumptions incorrect. Some birds could undertake major migratory movements after breeding — or some could winter much further north in the pack ice than had been thought.

We are grateful to Iain Stenhouse for thinking of our study when he found he had a few extra geolocators as his field season was ending and it is likely that the 2011-2012 data from our black guillemots will be just the start of their use on Cooper Island.


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