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.
Graduate student Drew Sauve recently returned from Cooper Island. He describes his collaboration with George in this guest post.
The Black Guillemots on Cooper Island are one of many wild populations that are responding to climate change by changing when they lay their eggs. These Arctic seabirds want to lay their eggs as soon as the winter snow melts and spring begins, because their breeding season—from first access to a nest cavity to departure of chicks—is 80 days, an exceptionally long breeding period for a bird. Parent guillemots have to have their young ready to fly off to sea before fall snow accumulation begins to block entrances to nest cavities. In recent years, with sea ice retreating offshore in late summer, early breeding has the benefit of being able to provision young when the preferred prey of Arctic Cod is still readily available.
While there are decades of data that show spring snowmelt is occurring earlier in northern Alaska and, allowing guillemots to lay their eggs earlier, my research is focused on whether Black Guillemots are evolving to lay their eggs earlier.
George has created a detailed banding dataset, where every parent has a numbered metal band, and a unique colour band combination; all of their nestlings are banded before fledging. Using this data set, I can construct family trees for the birds breeding on the island. Family trees or pedigrees are often used in studies of human health or livestock breeding. In the rare case where we have long-term pedigrees in wild populations, geneticists can use them to determine genetic variation in a trait—in this case, when birds lay their eggs.
The amount of genetic variation or the potential for genetic change in a key trait like egg-laying date could determine whether a population will be able to adapt to climate change.
The analyses we do with a pedigree are similar to what a farmer might do when trying to select cows that produce more milk. Some cows and their families might produce more milk, so the farmer would select those cows when breeding their stock. Instead of cow families that produce lots of milk, I tried to find guillemot families that laid their eggs earlier than others in response to snowmelt. However, instead of a farmer selecting cows I wanted to see if climate change was selecting for earlier breeding guillemots.
Ultimately, there were no family groups that tended to lay earlier than others. Using my farmer example again, this would be like trying to select a cow with high milk output when all the families of cows produced the same amount of milk. The farmer would be unable to improve their herd because all the cows are the same with regards to milk production.
What this means on Cooper Island is that Black Guillemots are unlikely to evolve earlier laying dates to match warmer temperatures and the change in laying-date we’ve observed so far is not because of evolution. Rather individual birds are behaviorally adjusting their laying date due to changes in snowmelt.
Unfortunately, this behavioural response to snowmelt doesn’t seem to be enough of a response as the birds are still struggling to raise offspring in the warming Arctic.
The Cooper Island data demonstrate the power of long-term, detailed data collection. Just as George did not intend to study climate change when he started the study in 1975, I also do not think he intended on collecting data that one day would be useful for building a pedigree with multiple generations of Black Guillemots, but he did just that.
The value of long-term datasets might not always be apparent when starting the study, but much of our understanding of evolution, behavior, ecology, and responses to climate change come from research that span decades. I suspect that the Cooper Island dataset and others like it will continue to be valuable in the future.
Hatching is finally over with one very late egg hatching today after having been incubated for 34 days; 28 days is normal. The oldest nestling is 16 days old; the chick is gaining weight and doing well like all of the other 45 nestlings.
While the main pack ice is well offshore, the Marginal Ice Zone, where ice covers from 18 to 80 percent of the ocean’s surface, extends south to the entire Alaskan Beaufort Sea coast, including Cooper Island. The seascape visible from the north beach now has widely scattered floes, some with rather high vertical relief breaking the horizon, in a nearly flat calm sea. This differs greatly from what was present last year when the first week in August had no ice visible with large swells breaking on north beach. More importantly, last year at this time the sea surface temperature was well above 4 degrees Celsius while this year it is less than 2 degrees Celsius. The guillemot’s preferred prey, Arctic Cod, are typically found in waters from -2 to 4 degrees.
The ice and water temperature conditions are ideal for the parent birds provisioning. Arctic Cod has comprised well over 90 percent of the prey being fed to chicks this year. The two oldest chicks, hatched on July 21, weighed 35 grams at hatching and now weigh 275 grams and 245 grams – the larger of the two experiencing an almost seven-fold weight increase in a 15-day period. A growth rate that rapid requires readily available prey that is both abundant and high energy, as well as two dedicated parents to return to the nest site with a fish every hour. Similar high growth rates are occurring at other nests.
This condition of the nestlings could not be more of a contrast with early August last year. Then, there was widespread mortality of younger siblings as parents could only find enough prey to maintain a single nestling. Arctic cod were absent for much of the nestling period with sculpin and juvenile sand lance comprising most of the prey. Guillemot parents turn to these alternative prey only when Arctic Cod are not available. Sculpin, with their large bony and spiny heads, are hard for nestlings to hold and swallow. They are frequently rejected with numbers building up in nest sites as the young wait for a more preferable fish.
For the moment our daily nest weighing and measuring of guillemot nestlings has been a very positive experience. However, based on what we have seen in the last decade, we know that conditions can change rapidly in August. A strong south wind could move the ice well out of the guillemots’ foraging range or warmer waters could move eastward from the Chukchi and drive away Arctic Cod. We also know that larger and older nestlings are more able to survive changes in prey availability and that the current high growth rates will allow more individuals to survive to fledging.