Birder’s Notebook: Rusty Blackbird – A common bird in steep decline
Every spring I watch for the arrival of rusty blackbirds with a mixture of hopeful anticipation and dread. Will they return? This is a species in the midst of what has been described as the steepest population decline of any songbird in recent history.
Thankfully, since learning in 2014 of their mysterious population drop from then-local ornithologist Peter Bente, these glossy, yellow-eyed blackbirds have shown up and nested reliably at all of the sites where I regularly look for them.
The rusty blackbird is a North American species that breeds widely across the boreal forest regions of Alaska, Canada and the Northeastern United States. It is a regular but uncommon and perhaps little-noticed breeder on the Seward Peninsula, where the bird is on the western edge of its breeding range.
There is no population trend information for our region, but the blackbirds have always been most abundant in the southeastern Seward Peninsula and Unalakleet areas. They are also found along many of our river drainages where tall shrub thickets grow, preferring open areas near water bordered by black spruce forest or tall willows.
Of the many migratory birds that come to this region to breed, the rusty blackbird is with us longer than most. They arrive as early as late April, often to a snowy landscape, and many remain through mid-September.
Following courtship, the female builds a sturdy nest, usually in a willow or spruce along the margins of a beaver pond, stream or wetland.
The male sings to his mate while she builds their bulky nest. She makes a structure of twigs, dried grass and lichens, then presses wet, rotting plant materials into the outer framework. This dries and hardens to form a solid bowl that she lines with fine grasses and plant fibers. They do not reuse their nests, but other species sometimes occupy them the following year.
Egg laying in our region typically begins about the third week of May. The female lays four to six eggs which she alone incubates for up to 14 days. The male brings her food, but he doesn’t deliver it to her in the nest. Rather, he perches nearby and she flies to him and begs with fluttering wings to be fed.
While the female incubates, both birds sing to each other, maintaining their pair bond.
Both parents feed the nestlings. This summer, I was surprised to see a third blackbird delivering food to a nest along the Nome River, and read while researching for this article that occasionally a second male helps feed the nestlings.
The naked young develop quickly and fledge only 14 days after hatch. In our region that is often in midJune.
Rusty blackbirds feed mostly on aquatic invertebrates and a wide variety of insects, especially beetles, caterpillars and grasshoppers. They also eat seeds and berries.
Walking or running along the edges of wetlands or shorelines, these blackbirds forage by probing their bills into the mud or turning over stones, leaves and sticks in search of prey. They will wade up to their bellies in shallow water like sandpipers and plunge their heads underwater to grab aquatic invertebrates. Sometimes they snatch mosquitoes and other flying insects out of the air.
Rusty blackbirds are not usually aggressive or territorial birds, but during cold snaps when food is scarce they have been known to kill and eat other birds such as sparrows and longspurs.
Owls, falcons and other raptors prey upon rusty blackbirds, and red squirrels take their eggs.
Migration begins in mid-August and peaks during the first half of September. Migrating by day, blackbirds pass through interior Alaska and northwestern Canada, sweeping southeast across central Canada and then heading south, ultimately ending up in the southeastern United States for the winter.
Over the last 50 years as rusty blackbird numbers declined precipitously, their disappearance went largely unnoticed.
On their wintering grounds the birds forage in huge mixed flocks with other, similar-looking blackbirds. From there they disappear into vast, remote and uninhabited northern forests where no one realized their numbers were dwindling.
Their decline first came to light in 1999 when ornithologist Russell Greenberg analyzed results from multiple long-term citizen-science bird-tracking projects and sounded the alarm. Since then, resources and research have been devoted to understanding the causes of the rusty blackbird’s decline in hopes of reversing the trend before it is too late.
In 2014, it was estimated that since 1970, 85 to 95 percent of the population disappeared. The North American Bird Conservation Initiative listed the rusty blackbird as a “Common Bird in Steep Decline. “
It is a complicated puzzle with many probable factors taking a toll on the rusty blackbird population.
Contributing factors include: Extensive loss of wetland habitat in their wintering areas; contaminant poisoning, particularly from mercury which bioaccumulates in wetland habitats; disturbance and loss of wetland breeding habitat in the southern part of their breeding range; climate change; and historic poisoning of blackbirds to reduce crop depredation. Poisoning is no longer legal.
Climate change is drying out boreal forest wetlands where the birds breed. Meanwhile species such as redwing blackbirds and common grackles are expanding into northern forests where they aggressively compete with rusty blackbirds.
The good news is that research in interior Alaska has found high rates of productivity, nesting success and survival. Absent studies here, this at least seems to be the case in our region, too. The threats facing our blackbirds appear to be the greatest during migration or on the wintering grounds.
Recent studies suggest the Alaska breeding population may be helped by where it winters.
Analysis of hydrogen isotopes in feathers showed that Alaska breeders winter west of the Appalachians in the Mississippi River valley, where some issues with winter habitat are less severe. Birds wintering west of the Appalachians also have lower levels of mercury in their bodies than those wintering along the east coast.
If rusty blackbirds are able to avoid the pitfalls of their winter range and migration route, could they be a climate change winner here as their tall shrub habitat advances over the Seward Peninsula? Only time will tell. For now, I’m grateful that these sleek blackbirds made it back once again to raise their young in our region.