Pelagic Ecosystems

Fall and Winter Marine Bird Abundance

A Black-legged Kittiwake surveys the ocean for fish. Black-legged Kittiwakes were one of the most commonly sighted seabirds during fall and winter surveys in Prince William Sound. Photo by Tamara Zeller, USFWS.

Who We Are

Mary Anne Bishop, Prince William Sound Science Center

Mary Anne Bishop, Prince William Sound Science Center

Pirouette above the sea,
dive fast on pleated wing
Sand lance for a meal

Why are we sampling?

Of the marine birds that overwinter in Prince William Sound (PWS), nine species were initially injured by the Exxon Valdez oil spill, including three species that have not yet recovered (marbled murrelet, Kittlitz’s murrelet, and pigeon guillemot). Long-term monitoring of marine birds in Prince William Sound during winter is needed to understand how post-spill ecosystem recovery and changing physical and biological factors are affecting bird abundance and species composition, as well as their distribution and habitat use.

Where are we sampling?

We conduct marine bird surveys throughout the open and nearshore waters of Prince William Sound, including in juvenile herring nursery bays such as  Zaikof, Whale, Eaglek, Lower Herring, Gravina, and Simpson. These surveys provide coverage in four different quadrants of Prince William Sound.

How are we sampling?

Prince William Sound Science Center biologist Bobby Hsu conducting marine bird surveys during winter in conjunction with EVOS-funded Herring surveys.

Prince William Sound Science Center biologist Bobby Hsu conducting marine bird surveys during winter in conjunction with EVOS-funded Herring surveys.

We conduct surveys between mid-September and March following established U.S. Fish and Wildlife Service marine bird survey protocols. One observer records the number and behavior of birds and marine mammals occurring along a strip transect that is 300 meters wide (150 meters on both sides and ahead of the boat, in distance “bins” of 50 meters). Additionally, we record any noteworthy observations out to 1 kilometer on either side of the boat.

What are we finding?

Seasonal patterns in marine bird distribution over 15 nonbreeding seasons were identified for 11 species groups in Prince William Sound. The study highlighted dynamic movements into and out of PWS during the nonbreeding season, challenging the notion of a single “winter” period for marine bird distribution. Habitat use remained consistent across analyses, with water depth, distance from shore, and habitat type identified as key environmental factors. Birds were more likely to be present and in greater numbers closer to shore and in shallower water. Our results support the assertion that birds seek refuge during winter, with PWS’s superior winter habitat relative to the harsher conditions in the Gulf of Alaska.

Key environmental factors influencing marine bird distribution in Prince William Sound were water depth, distance from shore, and habitat type. Most species groups were more likely to be present and in greater numbers when closer to shore and in shallower water. Grebes, murrelets, mergansers, and small gulls were less likely to be present in open-water habitats. On the contrary, cormorants were more likely in mouths of bays and passages and open water, scoters preferred mouths of bays and passages, and murres were more likely in open water compared to bays. We also found that more than 40% of birds were near fish schools, but only 20% of fish schools had birds around them. Overall, birds targeted fish schools that were easier to reach.

When observing bird-humpback whale foraging dynamics, we discovered that humpback whales use forage flocks of seabirds as signals to find scattered prey resources. In observed interactions, humpback whales consistently acted as flock disruptors rather than facilitators. This behavior involved a single whale surfacing through an existing feeding aggregation, causing the aggregation to disperse. The findings suggest that humpback whales disrupt forage flocks by accessing prey resources rather than cooperating with the flocks in their feeding activities.