The Rusty Blackbird is not colorful, and their song is closer to a rusty door hinge than it is to a woodwind melody. And their choice of habitats, boreal wetlands in the summer, and swampy wetlands of the southeastern US in the winter, are hardly post-card inspiring. And yet there is something about this bird that I find subtly elegant. Perhaps its their piercing yellow eye, or their sharp look that exudes something like intelligence. Indeed, there is just something about the Rusty Blackbird that I can’t help but love.
I hardly payed any attention to Rusties until a few years ago, when one of my projects as a Research Biologist was studying their breeding ecology. They’d drawn the attention of biologists and land managers since an analysis of historic bird data had shown a catastrophic decline in their population. The magnitude of the loss (95% over the last 50 years) caused alarm bells to go off across the species’ range.
At the time, no one really knew much about Rusties. They breed, as I noted, in boreal wetlands and people just don’t go tromping around those areas very often. The Rusty Blackbird had simply been overlooked.
And that is how I found myself up to my hip in swamp water on a chilly spring day. I was in the Tanana Flats, a big forest and wetland area just south of Fairbanks. It’s military land and is thus completely undeveloped despite its proximity to the second largest city in Alaska. Also, the hiking is absolute crap.
Much of the flats is composed of fens. Fens, for those who don’t know, are vegetation mats floating atop water. In my study area, they grew on the old, criss-crossing, oxbows of the Tanana. Moving from one place to another, there was no choice but to tip-toe these swaths of water-bed like vegetation. At their best, the fens bounce disconcertingly but are solid. Too, they can be thin, like a worn wicker chair, full of holes and hidden gaps. In the latter areas, your foot can break through to plunge into the bottomless water below.
As I tried to extract myself from my position (one leg straight down into the water, and the other bent with my knee in my chest) I felt around for some solid footing. Nothing. I don’t usually get creeped out by the natural world, but that unseen water gave me the willies. Was it possible, I wondered, to fall all the way in? Like breaking through ice to drown in the dark below?
“This!” I said to myself, “This is why people ignore Rusty Blackbirds!”. I extracted my leg, and limped delicately over to some solid ground surrounding a patch of spruces.
Emptying my rubber boots on the fen’s edge, I heard a Rusty Blackbird. Rusties have a distinctive “pop-wheee!” call that carries for hundreds of meters through the forest. My crew and I hadn’t yet surveyed this corner of our plot and this bird was new to us. When searching for new pairs and nests each day is an easter egg hunt and I always get a twinge of kid-like excitement when I hear a new bird call.
I found that bird’s nest, a meter up in the spreading branches of a willow. And with the help of my field crew we found a few dozen more over the course of the project. It was a great study, one we tied to work being done in Anchorage, Cordova, and across the boreal forest. The results were published in the ornithological journal The Condor, and followed up as an issue of Studies in Avian Biology.
This was all a few years ago, and I’ve fallen out of the Rusty Blackbird research network, so I was pleased when I got a preview pdf last week of a new study on Rusties that has just appeared in The Condor. Building on the previous work that I was a part of, this new study, which took place in Maine and New Hampshire, adds a new dimension to understanding the declines in Rusty Blackbirds: Conifer cones, and squirrels.
The study here took place over two years (2011-2012). One aspect of the project involved setting cameras to document activity at the nest, including nest predators. Predation is a common occurrence. Nest predators like ravens, raptors, jays, snakes, raccoons, and bears consume eggs and chicks at every opportunity. But determining who, or what was responsible for an empty nest is nearly impossible, without cameras.
Using 29 camera traps, the biologists documented 8 predation events. Two in 2011 and 6 in 2012 (this distribution turns out to be important). And they found a surprisingly diverse array of nest thieves including White-tailed deer, a small Accipiter (Coopers or Sharp-shinned Hawk), a Blue Jay, a probable Flying Squirrel, and Red Squirrels.
Red Squirrels were doing the bulk of the damage, all of it at the Maine site in 2012. That timing is important because in 2011, the conifers in Maine had a banner year for cone production. Lots and lots of cones were produced in that forest and the squirrels had a food bonanza. Their reproduction sky-rocketed and come 2012 the woods were full of chattering squirrels.
Which would have been all fine and good if the cone crop and continued to produce, but it didn’t. It collapsed, leaving a high population of squirrels with little to eat. And they turned to bird nests. The eggs and chicks of Rusty Blackbirds felt the heat and more than a few became squirrel food.
This isn’t a novel finding. Many bird studies, including some of those I was involved in here in Alaska, have documented Red Squirrels as nest predators. What’s new is tying that increased predation to the abundance (and lack thereof) of conifer cones.
Rusty Blackbirds eat aquatic bugs, not conifer cones. As a food source, Rusties don’t give a lick about pine cones. Spruces and pines are convenient places to nest and perch, but that’s about it. And yet, in this study, Blackbird productivity is closely tied to how many cones ripen on the trees.
Of course, cone crops have varied for millennia, and Rusty Blackbirds have presumably been impacted by them for just as long. So we can’t blame cones or squirrels on the current decline. But this study does illustrate the complexity of the world in which these birds live, and the number of factors that can impact population, or hinder its recovery.
Spruces – climate – cones – squirrels – bird nests… It’s such a perfect illustration of the way seemingly disparate parts of an ecosystem can be intimately connected. This kind of finding makes natural history and research biology so darned cool. We have the opportunity to learn something new, something important, just by dedicating the time to being outside, paying attention, and solving puzzles.
As we put pieces like this together, we can begin to see the keystones of an ecosystem, and where to dedicate conservation efforts. Maybe with enough of us paying attention, and figuring out these puzzles, we can even understand enough to solve the mystery of the Rusty Blackbird’s decline.
Then, hopefully, we’ll have the sense to do something about it.