Category Archives: feeding

Uncertain Future for Nestlings: Sea ice retreat shifts prey out of foraging range

George’s latest field report describes his daily nest checks as parents are feeding chicks to prepare them for fledging.

Arctic sea ice grows and shrinks during the year (seasonal cycle), reaching its annual minimum extent at the end of every summer (early-mid September). Currently, 2018’s sea ice extent is below the minimums from the 1980, 1990, and 2000 decadal averages. Image Credit: Zach Labe

Black Guillemots have their young remain in the nest for almost five weeks, being nearly adult weight and independent of the parents when fledging. Returning to the nest with a single fish in their bill is a breeding strategy found in all member of the genus Cepphus; it reflects the abundance and predictability of prey in the nearshore waters where parents forage while provisioning young.

For guillemots breeding in subarctic and temperate areas, where the nearshore provides a diverse and ample supply of forage fish, the strategy works well. In the Arctic, however, Mandt’s Black Guillemot has had to adapt to a different nearshore environment. Because of sea ice covering and scouring the nearshore much of the year, and the low productivity and biodiversity of the region’s marine waters, there is a typically a paucity of nearshore fish to feed their young.

The sea ice is central to supporting an ecosystem, with Arctic Cod being the primary forage fish, that can provide an abundant source of prey when the edge of the pack ice occupies the nearshore. Mandt’s Black Guillemot has been able to breed in the Arctic “nearshore” due to this presence of sea ice near their breeding colonies.

The strategy worked well as long the breeding colonies were adjacent to the Arctic pack ice and sea surface temperatures were low. These conditions were present for the first thirty years of the Cooper Island study and the growth and fledging rate of guillemot nestlings was high. Now, as summer sea ice retreats earlier and farther from the coast, nestlings and their parents could no longer count on having 35 days of high prey availability. This has resulted in decreased chick growth, increased mortality, and poor condition of those nestlings surviving to 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.

One of the reasons nesting guillemots are such good monitors of prey availability in nearshore waters is the lengthy time parent birds have to provision their nestlings, as guillemot young stay in the nest for five weeks after hatching. During that time parent birds are foraging for most of each day and returning to the nest nearly once an hour with a fish.

The current conditions of diminished sea ice have us approaching our daily nest checks with far more uncertainty than we did in the first decades of our study – when we expected chicks to have a steady growth rate until fledging. In the next few weeks a nest case could contain nestlings in poor condition, signs of hunger-motivated sibling aggression on the younger chick, or a number of large sculpin uneaten by the nestlings due to the size of their spiny bony head.

The one bright spot in our nest checks this year has been site E-11 where the chicks hatched from the first eggs laid this June. These nestlings are extremely healthy having been raised on adult Arctic Cod by two highly experienced parents, both over 20 years of age. The oldest nestling is just two to three days from fledging and demonstrates the benefits of parents laying eggs as soon as spring snowmelt allows.

Seattle science teacher returns from Cooper Island

Katie Morrison with nest box

Katie with nest box.

By Katie Morrison

Heading back to Barrow, we glide across the glassy Elson Lagoon and it is hard to imagine the wind-driven angry whitecaps that filled the lagoon just a few days before. But tonight it is calm and still and we travel with ease in our open skiff. I am glad to be wearing the precautionary orange survival suit, for though it is a lovely evening, it feels quite cold to me. It’s after ten o’clock at night, the sky is filled with shades of orange and pinks and purples, and the midnight sun seems not quite as high in the sky as it was a few weeks ago. Flocks of eider ducks race past our boat in long lines, framed by the colorful sky. As my boat pulls away from Cooper Island, I wave goodbye to George with Max and Penelope, who’ve just arrived to help finish the field season. As Cooper Island gets smaller and smaller in the distance, it is still largely present in my mind.

George banding Black Guillemots for identification

George banding Black Guillemots for identification

I’m excited to arrive in Barrow, have a hot shower, and fly home to see my friends and family and tell them my stories. But at the same time, I am already missing the peeps of the newly hatched chicks, the golden rocks on the island, the always-surprising site of the giant spool on the horizon of the West Beach, and the routines of field work.

During my stay, 133 chicks hatched in 114 nest sites. Since I have gone, 37 more chicks have hatched, bringing the current total to 170 chicks. It has been a good year so far for the Black Guillemots breeding on Cooper Island.  The retreat of sea ice has not been as extreme as in recent years and this means the guillemots’ preferred prey of Arctic Cod, which prefer cold waters, are still abundant for the growing chicks.  In past years, the early disappearance of ice resulted in a decrease in the Arctic Cod population, which led to large numbers of nestling deaths and low weights for those chicks that did fledge. This year parent birds have been bringing primarily Arctic Cod to feed their young and George, with field assistants Max and Penelope, has been busy collecting data about the prey sources. They have been deploying TDRs (temperature depth recorders) on parent birds that collect dive time data and where in the water column the birds are fishing. They are also using real-time photography and motion-sensitive time-lapse cameras to monitor and correlate the fish species being caught and brought back to the nests. Coupling the fish species identification with the TDR data, George will learn a lot about the condition of prey abundance in the Arctic Ocean around Cooper Island.

A Black Guillemot in possession of its favorite food -- Arctic Cod

A Black Guillemot in possession of its favorite food — Arctic Cod

I am anxious to hear if the Arctic Cod supply remains steady this year or if it begins to decline and the Black Guillemots are forced to switch to less nutritious prey for their young. I worry for the 170 chicks that need about a fish an hour to maintain their rapid growth rate so that they can fledge before the first snows come. In the back of my mind, I also worry about what this means for the overall conditions in the Arctic and how climate change is affecting the rest of the world.

A 2013 season Black Guillemot chick

A 2013 season Black Guillemot chick

I am back in Seattle and getting ready for the new school year, but in my mind I can still walk through the colony with George. I don’t own the story and details of each nest site (each with its own letter-number code) the uncanny way George does. But some sites still stand out in my mind:

C-13, the First Chick found in 2013! We were delighted to open the nest box and see this fluffy chick. How is that little one doing? As one of the oldest in the colony, has it fledged?

L-5, Katie’s Site. On one of my first days on the island, I discovered late-nesting birds in this nest box. Early on, the parents seemed unsure of how to take care of the nest and we would sometimes find the two parents together, flirting right outside the nest box, while eggs inside were unattended! They eventually settled down and the eggs should hatch soon. If the snows come late, there is a chance these late chicks could fledge.

O-2, the Mini-Mansion. In this site, the nest box sits at one end of a long, skinny upside down wooden floorboard, left behind by the Navy in the 1960s. The parent birds chose to nest under the floorboard and right next to (but not in) the nest box. During my stay we had three days of sustained high winds and one evening we discovered the entry sanded in and the two chicks trapped inside. We worked frantically to dig them out and were relieved to see that the chicks were fine.

I’m looking forward to George’s return to Seattle and hearing about the conclusions of the 2013 field season that I was so lucky to be a part of.