CORVALLIS, Ore. – Less favorable ocean conditions mean marbled murrelet chicks take longer to leave the nest, making them more vulnerable to predation, according to a new study of the iconic Pacific Northwest seabird by Oregon State University scientists.
Findings were published today in the journal Ornithology .
The research, which quantified how murrelet parents provided food for their young under different ocean conditions, is important for understanding how the secretive species might fare as climate change alters the ocean environment, said the OSU College of Forestry's Jim Rivers, director of the Oregon Marbled Murrelet Project .
Scientists use multiple indicators to measure ocean conditions from an ecological perspective, Rivers explains, but overall poor conditions often mean "it's warmer and there's less food available."
"And in really bad years, murrelets may forgo breeding altogether," he said.
Murrelets can only produce one offspring per year, and their young require forage fish for proper growth and development.
Adult marbled murrelets spend most of their time in coastal waters eating krill, other invertebrates and fish such as herring, anchovies, smelt and capelin. The dove-sized birds are closely related to puffins and murres, but unlike those birds, murrelets raise their young as far as 60 miles inland in mature and old-growth conifer forests.
Murrelets typically lay their single egg high in a tree on a horizontal limb at least 4 inches in diameter. The birds are monogamous and the parents take turns bringing fish to their offspring, usually in the early morning or late evening.
Steller's jays, American crows and common ravens are the main predators of murrelet eggs and chicks.
"Murrelets have secretive nesting behaviors that help protect their young from predators," said Cecelia Frisinger, a graduate student who led the study. "They also commute long distances from ocean feeding areas to inland nesting sites, a behavior that is highly unusual among seabirds. Together, these traits make conducting research on these birds especially challenging."
Frisinger, Rivers and collaborators at Oregon State used more than 12,000 hours of video recordings to study marbled murrelet chick provisioning at 18 nests over two years of poor ocean conditions and two years of more favorable conditions. Analyzing 1,332 feeding events, the scientists found the chicks received fewer feeding visits per day – consisting of a single fish per visit, typically a smelt, anchovy, herring or sand lance – when ocean conditions were poor.
However, the chicks' estimated daily energy intake was only slightly greater during better ocean conditions because when conditions were poor, the fish the chicks received were larger and more energy dense.
Nevertheless, under poor ocean conditions, the chicks took an average of 25% longer to fledge, or eight days longer, greatly increasing their exposure to nest predators.
"This study includes more marbled murrelet chick provisioning observations than all previous studies combined, making it the largest dataset of its kind to date," Frisinger said. "Determining variation in behavioral traits, including parental care behaviors that buffer reproductive output against changing environmental conditions, is critical for predicting how animals will cope with climate change."
The findings suggest that successful murrelet reproduction depends on a narrow range of prey species and that climate-driven changes in those species' availability will affect murrelets' reproductive output, she said.
Along the West Coast, marbled murrelets can be seen from Santa Cruz, California, to the Aleutian Islands. The species is listed as threatened under the U.S. Endangered Species Act in Washington, Oregon and California.
Projected increases in ocean warming coupled with the loss and fragmentation of murrelet nesting habitat suggest that murrelet population recovery will require conservation efforts in both marine and terrestrial habitats, Rivers said.
"On the marine side, we need to enhance populations of murrelet prey items by reducing bycatch of forage fish and protecting spawning areas," he said. "Those actions will also benefit large predatory fishes, other seabirds and marine mammals, whose populations are also dependent on the long-term health of forage fish stocks."
The U.S. Department of Agriculture National Institute of Food and Agriculture and the OSU College of Forestry supported this research, which was conducted in Rivers' Forest Animal Ecology Lab. The study also included Oregon State's Matt Betts, Dan Roby, Kim Nelson, Elizabeth Daly, Jonathan Dachenhaus and Kaitlyn Osborne.
