Poor ocean conditions delay marbled murrelet chick fledging
A new study finds marbled murrelet chicks take eight days longer to fledge when ocean conditions are poor, reducing feeding frequency and increasing predation risk for the threatened seabird.
Marbled murrelet chicks take 25% longer to fledge under poor ocean conditions, requiring an extra eight days for development. This significant delay increases their exposure to nest predators and threatens reproduction for a species that raises only one chick per year.
Reduced feeding frequency under poor ocean conditions
When ocean conditions were poor, chicks received significantly fewer feeding visits from their parents each day. Each visit delivered just a single fish. The reduced provisioning rate directly contributed to the slower growth observed in the nestlings.
Limited energy gain despite larger fish
Interestingly, the fish delivered during poor ocean conditions were larger and more energy-dense. Despite this, the chicks' daily energy intake increased only slightly. The infrequency of feedings outweighed the benefit of receiving bigger prey items.
Comprehensive study methodology and scale
The research provides the largest dataset of its kind on marbled murrelet nesting. Scientists analyzed 1,332 feeding events from over 12,000 hours of video recordings. The footage was gathered at 18 nests over two years of poor and two years of favorable ocean conditions.
The research team from Oregon State University included Jim Rivers, Cecelia Frisinger, Matt Betts, Dan Roby, Kim Nelson, Elizabeth Daly, Jonathan Dachenhaus, and Kaitlyn Osborne.
Threatened species context
The marbled murrelet is listed as threatened under the U.S. Endangered Species Act in Washington, Oregon, and California. Adults spend most of their time in coastal waters, feeding on krill, invertebrates, and forage fish like herring, anchovies, smelt, and capelin.
They raise their young far inland, up to 60 miles (97 kilometers) from the coast, in mature and old-growth conifer forests. There, they lay a single egg high in a tree on a broad horizontal limb. Monogamous parents take turns bringing fish to the chick, usually in the early morning or late evening.
Poor ocean conditions, characterized by warmer waters and less food availability, force adults to hunt for the specific forage fish chicks need. Key predators like Steller's jays, American crows, and common ravens pose a constant threat to eggs and chicks during the extended nesting period. Conservation efforts must therefore address both marine and terrestrial habitats to support population recovery.
