Nature, Human Activities Create Challenges for Declining Songbirds
Alumna publishes paper on rusty blackbird study
A former ESF graduate student's research into the lives - and deaths - of young rusty blackbirds could help scientists learn more about the complex connections between human activities and the well-being of rapidly declining species.
Shannon Buckley Luepold, who earned her master's degree from ESF, said the study she conducted as part of her thesis work suggests the impacts of timber harvesting on rusty blackbirds are probably more nuanced and complex than previously thought.
"It's not a simple good or bad, black or white sort of scenario," Luepold said from Manchester, England, where she currently resides. "It depends a lot on the context."
The results of the study were published today (Oct. 7, 2015) in the journal "The Condor: Ornithological Applications."
Luepold and her team looked at selection of breeding habitat by the rusty blackbird, a medium-sized bird a little larger than the more common red-winged blackbird. Their habitat is typically wet areas that provide room to forage under leaves and debris on the ground. The rusty blackbird population is in rapid decline.
"This bird lives in wetlands, migrates to the southeastern United States and breeds in Canada and the northeastern United States, including the Adirondacks," said Stacy McNulty, an ecological researcher at ESF's Newcomb Campus who served as Luepold's graduate adviser. "Rusties declined precipitously a few decades ago, and we and other researchers are trying to determine why the population decline is occurring, given they don't migrate out of North America."
The study was conducted in intensively managed forests in northern New England; the goal was to assess how the habitat around nests affected the survival of the young. The study focused on two populations, one each in New Hampshire and Maine, during 2011 and 2012. To identify predators, the researchers installed motion-triggered cameras near nests.
Luepold said the study was a follow-up to one conducted in Maine in 2006-08, in which researchers found a negative correlation between timber harvesting and rusty blackbird nest survival. The authors of that previous study suggested that red squirrels were the primary predators of rusty blackbird nests and that timber harvesting around wetlands encouraged rusty blackbirds to nest further into upland areas where there were more red squirrels. This suggestion was never proven, however.
"Our results were interesting because they agreed with those of the previous study in some aspects but not in others," Luepold said.
Her study did not find that timber harvesting had an effect on rusty blackbird survival. The birds prefer to nest in young conifer stands that regenerate after an ecological disturbance. The study found the birds did well in these habitats even when they were the result of timber harvesting. "That said, we found a strong association between nest survival and dense vegetation around the nest, so practices like pre-commercial thinning, which reduces tree density, could be detrimental," Luepold said.
As the researchers in the previous study had suspected, Luepold's cameras showed that, at least in Maine, red squirrels preyed on rusty blackbird nests more frequently than other animals did. The involvement of the red squirrels, however, occurred in 2012, a year after fir and spruce trees produced a particularly abundant cone crop. Those cones are red squirrels' primary food. The timing made Buckley wonder if there is a regular cycle linking cone production, red squirrel populations and nest predation. The connection between red squirrel predation and timber harvesting, however, was not strongly supported.
"Our study highlights how the impacts of timber harvesting, as well as many other anthropogenic activities, on other species are often more nuanced and complex than people realize," Luepold said. "Another aspect is that it deals with a bird many people have never heard of, let alone care about. Although the recent conservation concern about rusty blackbirds has raised their profile somewhat, they are still viewed by many as just 'another blackbird.'"
Though they lack the striking coloration of some easily recognized songbirds, rusty blackbirds have their own unique traits. Both the males and females sing, which is unusual. Throughout the year, they are strongly tied to wet areas where they find aquatic insects. Because of this, they time the different stages of their lifecycle, such as migrating and nesting, to coincide with the availability of insects such as damsel and dragonflies, caddis flies and other aquatic insects. Occasionally, they catch tadpoles and minnows.
The female alone builds the nest, with her mate singing nearby. When she's incubating, the male often brings her food and feeds her at the nest or on a perch close by. Sometimes the birds nest in small, loose colonies, with multiple pairs within a couple hundred meters. After the young fledge, the adults sometimes group the young together in a sort of "crèche" and the adults look after them communally.
Squirrels are not their only predators. Luepold has photos documenting that blue jays, hawks and even white-tailed deer disturb rusty blackbirds' nests.
"Though they are not brightly colored songbirds that migrate to tropical locales, they are nonetheless an unusual and fascinating species, about whom we still have much to learn," Luepold said. "I hope that our study will not only be a useful contribution to the body of scientific information on the species, but also serve to further raise awareness of and enthusiasm for rusty blackbirds among the public."
Also participating in the study were Thomas Hodgman of the Maine Department of Inland Fisheries and Wildlife, Dr. Jonathan Cohen of ESF and Dr. Carol Foss of New Hampshire Audubon. Working with Luepold as field assistants were ESF undergraduates Linnea D'Amico and Sara Prussing.
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