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.
Read George’s full report at Proteus.
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.
George’s latest field report describes his daily nest checks as parents are feeding chicks to prepare them for 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.
Read about this year’s nest checks and growth rates at Proteus.