By Joan Collins
One of North America’s most rapidly declining songbirds, the rusty blackbird, has lost 85% to 99% of its population in the past five decades.
This ongoing, mysterious disappearance flew under the radar for years, perhaps due to this dark species blending in with other large, mixed blackbird flocks in winter. Eventually, Christmas Bird Count data revealed a steep decline. The little-known blackbird has become a focus of research, but they’re tough to monitor.
Males are glossy-black with a blue-green sheen in breeding plumage (dark brown with rusty edging in winter, thus their name). Females are a brown to rusty color with a pale eyebrow. Both types have light-yellow eyes. The male’s song resembles rusty hinges creaking. Their call note is a hard “chek” sound.
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Breeding ranges run from Alaska, east across the boreal forests of Canada to Newfoundland, north to tree line, south to the Adirondacks and northern areas of Maine, New Hampshire and Vermont. They winter in the eastern U.S.
Spring arrivals
An early migrant, rusty blackbirds return to the Adirondacks in April. Breeding habitat includes wet forests often with dead standing trees near fens and bogs, and swampy shorelines of rivers, streams, lakes and ponds. In the Adirondacks, they like beaver-created wetlands. In the winter, they use wet woodlands and pond edges.
They build nests in living and dead trees, and shrubs, from 1.5 to 18 feet above ground. In early June 2020, we observed a rusty blackbird nest with young along the Vanderwhacker Mountain Trail in a beaver-created habitat. It was approximately seven feet high in a short, dead conifer. As the adult birds carried food to the nest, they were continually harassed by nesting olive-sided flycatchers.
In the breeding season, they feed on aquatic invertebrates, insects such as dragonflies, beetles and caterpillars, and snails. Grasshoppers form a large part of their diet outside of winter. One fall day, we observed a migrant rusty blackbird foraging along the Massawepie Mire Trail. It would hop from the dirt road trail into the roadside vegetation to flush grasshoppers into the open and then quickly grabbed them. In winter, their diet shifts to acorns, pine seeds and fruit.
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Unexplained population loss
Listed as “vulnerable” by The International Union for Conservation of Nature, the rusty blackbird is facing a high risk of extinction in the wild. Partners in Flight warns it is a “common bird in steep decline.”
There is no clear cause for the population loss. On the breeding range, a warmer climate has increased the frequency, intensity, and extent of fires and drying of boreal wetlands. The southern Canadian boreal forest has been impacted by timber harvesting, agriculture, mining and oil and gas development, and wetlands have experienced degradation from industrial pollutants. High levels of mercury have been found in rusty blackbirds in the northeastern U.S. and eastern Canada.
On the winter range, about 80% of bottomland hardwood habitats in the U.S. have been converted to agriculture. Extensive control programs to kill “nuisance” blackbirds such as red-winged blackbirds, common grackles and brown-headed cowbirds, went on for years in the southeastern U.S. Although not considered a crop pest, rusty blackbirds join other blackbird flocks in winter, and the program likely inadvertently killed some.
Other threats
The species is patchily distributed in low densities across its vast breeding range. Due to the migratory nature of the species, they may not have viable breeding populations as their numbers decline and it becomes harder to find a mate. This may explain range contractions in regions, such as the Adirondacks, where there is still appropriate breeding habitat, but is now unoccupied.
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Nest predators such as red squirrels, raptors, Canada jays, blue jays, common ravens and deer, are also threats.
The birds arrive earlier in spring than other species and can be hard to detect. After their young fledge, rusty blackbirds range over a larger area. In winter, they often blend in with other blackbird flocks.
The Madawaska Trail had been a reliable place to observe them fledging their young. Their sudden disappearance from this location in 2023 was discouraging.
It would be helpful to have a specific monitoring program in appropriate Adirondack wetlands to assess the decline. As some researchers have pointed out, if they were “cuter,” and not “just another blackbird,” we might have such a dedicated state-sponsored program.
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Joan,
I am always quick to blame deer overpopulation and consequent overbrowsing for ecological imbalances. I didn’t not know deer were nest predators on this species. But more importantly, the 5-6 foot browse line created by deer anywhere they are prevalent destroys a great deal of bird-breeding habitat and opens the area for even more intense nest predation.
While this is not likely the major stressor on Rusty populations/breeding, but it may be more significant than we think.
Sorry for the double-negative. Typo or brain fart.
Thanks, I was wondering what sort of problem was created by the deer?
It’s funny lots of what was agricultural land around parts of NYS has been converted back to woodlands so the 80% surprised me.
Also, I would have thought that all the conservation easement purchases over the last few decades in the nesting areas described would have helped as opposed to hurting their habitat?
Paul,
Your questions illustrate the complex nature of population dynamics. Restoring populations isn’t always as simple as restoring habitat. There could be a dozen or more other stresses on the species – including nest parasitism, predation, and low reproductive success – that are contributing to their decline. Indeed, these stresses are usually additive, and some species just are not resilient enough to rebound. Case in point – Passenger Pigeons.
I know. I was mainly pointing out that this one particular factor may be better for them. Sorry I shouldn’t have use a question mark but a period instead.