In late February, on a cold, breezy day with occasional snow flurries, I traveled up to the shore of Lake Erie with my advisor Dr. Tonra, and fellow grad student Kristie Stein, to erect 30-foot high automated telemetry towers. Hard to believe in those weather conditions, but some of the first north-bound migrants were already starting to arrive in northern Ohio. Rusty Blackbirds (affectionately known as “Rusties”) are early migrants, with many birds leaving their wintering grounds in the southeast U.S. in early March. So while Alicia was happily tracking “wintering” Swainson’s Warblers in sunny Jamaica (see her post below), I was gearing up for “spring” migration in frigid Ohio – I swear I’m not jealous.
Seriously, despite their meteorologically inopportune migration timing, Rusty Blackbirds are actually a really cool species, and it’s well worth braving the cold to learn a thing or two about them. A once abundant species, their numbers declined drastically throughout the 20th century, and they are now a species of conservation concern for many states and Canadian provinces. Rusties breed in wetland areas of the boreal forests, and winter across the southeastern U.S. around bottomland hardwood swamps; my research on the species takes place in the time between, during migratory stopover events in spring and fall. The Western Lake Erie Basin, specifically Ottawa National Wildlife Refuge and Magee Marsh Wildlife Area, has been identified as a migratory hotspot for the species, and thus a great location to learn about their migratory behavior.
The objectives of the season are easily stated: deploy 30 radio transmitters on Rusty Blackbirds, track them daily to find foraging locations, perform vegetation surveys at these locations to learn about their habitat requirements during migratory stopover, and continue tracking these individuals until they depart the study site. After getting the telemetry towers up and running (more about them later), the next order of business was capturing Rusty Blackbirds, which I did successfully on March 15 with the help of fellow grad student Elizabeth Ames and field technician Kellene Collins. The nanotag radio transmitters I deployed on Rusties are all on the same frequency, but each has a unique digitally encoded identifier, so when I track them with a handheld receiver, I can follow multiple individuals at once if need be. These tags are especially handy for use with the automated telemetry towers. The towers are set to scan continuously on one frequency, detecting all tags on that frequency. We operate 10 towers around the study site and spread across Western Lake Erie, as far north as Detroit River International Wildlife Refuge in Michigan, so we can get accurate estimates of departure times and track the large-scale movements of birds after they depart the immediate study area. The tags I use may also be detected by the much larger Motus array of towers, operated by Bird Studies Canada, which will allow us to follow the approximate paths of individuals even beyond their departure from Lake Erie.
Once I got the first tag deployed on March 15, we were off and running, with more tag deployments a week later, and then on April 10th, 12th, and 19th. Between deployments, Kellene and I were constantly tracking individuals and performing habitat surveys, as well as downloading (and troubleshooting) tower data. And aside from a cold snap and snowstorm in early April, the weather mostly cooperated!
Even before any extensive analysis, the data have given us several interesting surprises. First of all, stopover duration was much longer than expected for spring migrants, with many birds remaining for well over 3-4 weeks. Secondly, perhaps related to the long stopover duration was the presence of a migration molt in nearly all captured birds. We knew that most Rusty Blackbirds undergo a partial pre-alternate molt on the wintering grounds, but we did not expect so many birds to still be in such heavy body molt in the middle of their migration; perhaps the completion of this molt is the purpose of the long stopover duration. Finally, we were excited to find that nearly all the tagged birds made their departure from the site at night, meaning that they are nocturnal migrants like warblers (at least in the spring). Until now it had been supposed that they migrated during the day, like other blackbird species.
My last bird to depart (the infamous 66!) waited until all my other birds had been gone for several days before he finally made his night flight on the evening of May 16, for a minimum stopover duration of 28 days. I returned home to Columbus the following day, where I’m now helping Elizabeth Ames and Kristie Stein in their respective field seasons, studying Prothonotary Warblers and Black-crowned Night Herons. Long live field work!