Bobolink

 Bobolinks

This summer, we had a close-up experience with a pair of nesting Bobolinks in our fields. It was thrilling to venture out on the deck early in the morning each day and listen to this extraordinary and unique song. First, some background history.

Mr. Bobolink, annoyed at my close approach in his territory.

The Bobolink is a wonderful character in the dramatis personae of American birds. Still reasonably common, it is, unfortunately, in decline, along with many other American grassland birds. In Vermont, Bobolinks have been the subject of conservation programs spearheaded by Allan Strong in concert with many other conservationists. Vermont had an abundance of grassy habitat suitable for nesting in the early 1900s, thanks to forest clearing by the logging industry and by farmers. In recent decades, forests have regrown and squeezed the Bobolink. Further trouble comes from a conflict between the nesting schedule of the bird and the production of hay for livestock. The ground nests of the bird, in lush tall grasses, come to fruition just as many farmers need to cut and collect the crop. The Bobolink Project created a financial incentive for farmers to alter their haying schedule and allow the nests to finish. This effort is ongoing.

I have noticed Bobolinks singing in our neighborhood for a few years, so they must have figured out how to make it work despite all the mowing. This year, it was exciting to hear the songs at close range on May 14. (The species name is an obvious onomatopeia.) A colorful male was vocalizing early in the morning to advertise a promising territory to potential mates. The females are cryptically colored and mostly silent, and it took me at least a week to notice that one of them had been drawn in by all the commotion.

I’m pretty sure that a pair attempted to nest last year (2022) in my neighbor’s field, but he cut his hay in June on his usual production schedule, and I seriously doubt that the birds were able to pull it off. Maybe it could happen this year? Apparently our birds had chosen a different spot a hundred meters or so away, and were spending a lot of time on our side of the fence. Our field typically gets cut much later, in July, so they had a chance here. I got in the habitat of looking intently early in the morning to figure out exactly what they had in mind. By early June, I was starting to see one of the birds fly in, disappear in the grass for a few moments, and then fly off. I employed my spotting scope, and secured the indisputable evidence on June 21: the adults were carrying food into the tall grass.

The adults arrive with a meal and prepare to feed the concealed chicks.

There were chicks! In the weeks leading up to this moment, I had not detected a single sign of nest building. The birds had done so in utter stealth, despite the fact that the nest was only about 60 m from my back door. Amazing.

Early on June 23, I noted that the adults were coming in to feed every 5 to 10 minutes. This continued for another week or so. We were undeniably the proud owners of a Bobolink nest. Now, there was only one problem.

A "multiple-use" breeding ground!

Our field, for many years, has hosted cows all summer long. This year’s herd of seven was rotated in during the same time period that the Bobolinks were incubating. The bovines were happily marching to and fro in the same piece of ground, and one single step would have been the demise of this nesting attempt. Somehow, disaster had been averted. My local livestock expert tells me that the cows are likely to step aside when they sense that activity is close at hand, which I find plausible. Have Bobolinks evolved an ability to tolerate mammals in the neighborhood? I now suspect that is true. (So long as the mammals are not predators.) So, mowing is clearly a terminal event for a Bobolink nest, but cows on the march apparently is not.

I had a conversation with Kevin Tolan later in the summer. He was not surprised that they would have tolerated nearby cows, so long as the herd was not massively large. I asked if he could help me find the nest, now that the family had departed. I think he said, “Good luck with that.” Despite the fact that I know the nest location within about 5 m or so, I have been unable to find it after at least an hour of searching. Bobolinks have an incredible ability to hide their nests, which others have noted and which I now appreciate first hand. I searched for the nest just after the birds departed, after the field was subsequently mowed, and after more grazing had occurred, but failed each time. These Bobolinks are simply masterful at finding just the right portion of a grassland to conceal their nests.

By June 25, the chicks had become mobile. The adults were now feeding them about 50-100 m away from the nest site, although the chicks were still invisible in the grass. By July 15, they had departed altogether, although they did not go far. As Kevin Tolan had informed me, Bobolinks will “flock up” after fledging, and I have seen a large group of adults and immature birds a few hundred meters away, in another unmowed field. As of mid-August, I am still hearing an occasional “sproink” in fields along the road, although it’s got to be the case that the flock is starting to move south. They will head all the way to South America to spend the winter. Farmers in that part of the world (Argentina, Paraguay) have not been very graceful about hosting them, and they sometimes get shot or poisoned in the belief that they are harmful to crops.

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The Bobolink’s range was probably mostly in the prairies of the Midwest and Canada, in historic times. They moved east when forests were cleared in the 1700-1800s. The grasslands springing up in Vermont are different ecologically than in Nebraska and the Dakotas, but abundant rainfall makes for a vegetation density that just works well for them. This is a great example of opportunism, that consistent character of all bird species. Birds are constantly on the lookout for a suitable place to breed and to forage. Often, natural disturbances will create some habitat at least for a few decades or so – in Vermont, it can be windstorms that cause a lot of tree fall. But if human activities create habitat patches, the birds will invade just as readily. Species ranges are constantly expanding in some places, contracting in others, and the bird’s nesting habits are the quickest and surest signs of habitat change that any biogeographer could ever hope for. Most of the time, the event getting birders depressed is the loss of species from habitat change, about which much has been written. The Bobolinks in my back yard are a happier example of a species on the move continentally. A less-than-happy example is the Brown-headed Cowbird, which moved both east and west to take up with large herds of cattle, probably at the same time that Bobolinks moved. (Cowbirds cause serious damage to other species by being parasites on their nests.)

There is a fair question to ask about conservation. Should we be expending effort to help Bobolinks in Vermont, where they were historically absent? The same question is being asked about the Grasshopper Sparrow, which breeds in only a few spots on anthropogenic grassland in Vermont.

I don’t think it’s helpful to say anything on this topic unless one takes the bigger picture. What is happening to the species elsewhere in its original range? Bobolinks have suffered greatly from the loss of prairie grassland to crop cultivation. Wheat, corn, soybeans and lots of other things are being grown today where Bobolinks once thrived. This is the main reason for their decline. So if human activity has created habitat in places like Vermont, we have an opportunity to strengthen the continent-wide population by conservation actions, despite the artificial aspect of the habitat.

There are many other examples of anthropogenic range expansion in North American wildlife. Coyotes have spread throughout eastern North America, facilitated by Wolf killing. The House Finch was formerly a western bird but became continent-wide after reintroductions. The Cattle Egret moved to North America and found livestock herds to be suitable. Woodpeckers moved into the midwestern US when trees were planted in former prairie. I have not read any good literature on it, but Red-tailed Hawk may have benefitted from agricultural clearing. To be sure, these range expansions are not always a good thing. The invasion of Blue-winged Warbler into regions previously limited to Golden-winged Warbler has been a threat. Mallards have expanded into the range of American Black Duck. Barred Owls have moved west into territory formerly reserved for Spotted Owl.

But the Bobolink seems to be a different case. There are no known negative impacts of the spread of Bobolinks to formerly forested areas. Their appetites for caterpillars are likely helping eastern farmers. We hope to see them return to our fields in the years to come.