Opportunism

 Opportunism and bird migration

Pondicherry National Wildlife Refuge, New Hampshire

Migration for this autumn season brought a few nice surprises to our area. In late August and early September, we enjoyed the usual warbler show in our driveway, where a line of Balsam Firs provide a suitable place to forage. We had Cape-May Warblers, Bay-breasted Warblers (a few with some bay still on the flanks), American Redstarts, many Black-throated Green Warblers, one snazzy Wilson’s Warbler, Black-and-white Warblers, Tennessee Warblers, Nashville Warblers, Common Yellowthroats, Northern Parula, Magnolia Warblers, Blackburnian Warblers, Chestnut-sided Warblers, Yellow-rumped Warblers, Red-eyed Vireo, Blue-headed Vireos, and a few Scarlet Tanagers. Not bad.

Wilson's Warbler, Danville, Vermont. Peeking out from the interior of the vegetation.

Black-throated Green Warbler in its fall plumage. Newport, Vermont

Each migration season brings a reminder that birds have been such a successful life form due in part to a facility for opportunism. Migrating birds need stopover points with abundant food to fuel the long journey. They will be found in the kind of undisturbed habitat patches that you read about in field guides. But in addition, they are found in transient patches that just happen to arise on the route. The birds don’t seem to care whether the food (insects and caterpillars, for warblers and vireos) is provided by mature forests or by gardens and back yards. Shorebirds, herons, and egrets are drawn to healthy wetlands, but man-made wet areas will do, at least for a few hours or days of the journey. To be sure, all forms of wildlife seize on opportunities to feed, but the special mobility conferred upon birds gives them an extraordinary ability to find the smallest bit of far-flung habitat.

The local community of birders in my area has helped me to find a few of these patches. A cornfield beside the Passumpsic River in Saint Johnsbury has drawn in dabbling ducks in spring and fall, when either rain or snowmelt fills it up to a suitable level. Fruit trees around our grocery store parking lot sometimes bring in Bohemian Waxwings in the winter. Shorebirds will make use of flooded farm fields, too. I have spent time tracking down Upland Sandpipers and Buff-breasted Sandpipers in Delaware ag fields (especially sod farms), and I’ve seen Greater and Lesser Yellowlegs and Killdeer in fields close to home.

Birders are no less opportunistic than the birds. If the birds happen to be there, why not stop and look at them? Even when the scenery is – ahem -- not winning any awards, shall we say.  In New Mexico, west Texas, and Arizona, sewage treatment plants become an accidental food source to shorebirds, dabbling ducks, and herons. The Tucson sewage plant is famed among birders: I went there once for a Least Grebe, a rarity from south of the border. (It is comically named "Sweetwater wetlands.") We once ventured to the sewage plant of forlorn Lordsburg, New Mexico to see a Black-bellied Whistling Duck. Similar ponds in New Mexico gave me a chance to see White-rumped Sandpiper, Semipalmated Plover, Short-billed Dowitcher, Wilson’s Phalarope, Red-necked Phalarope, Baird’s Sandpiper, and Solitary Sandpiper. All of these were in places that were arid for tens of kilometers in all directions. (Except for the Rio Grande, which does not form mudflats that attract shorebirds, having been channelized by order of state legislatures.) It demonstrates how shorebirds, while flying thousands of miles south in the fall, mostly over dry land of the interior US, will not pass up an opportunity to exploit a wetland, small though it may be. A sewage pond lacks mud, the key ingredient for shorebird dinner, but it does possess insects in copious numbers.

In Vermont this fall, a birder alerted me to a Solitary Sandpiper in a flooded pasture nearby. Intrigued, I went there and found a pair of Stilt Sandpipers, a rarity away from lakes and oceans (at least in the East). The spot, on Old Silo Road near Barnet, is interesting. In the floodplain of the Passumpsic River, water collects there in spring and fall for a few weeks at most, before disappearing by evaporation and slowly draining to the river. Hoof action from the cows gives rise to mud and shallow puddles that mimics the mudflats around marshes. It becomes a bit of a shorebird magnet. Solitary Sandpipers were there for the whole season. The pair of Stilt Sandpipers stayed only a day (so far as we know). But what a day it was, for the nutritional requirements of a long-traveling sandpiper. Stilt Sandpipers breed in the Canadian arctic, and then fly as far south as Argentina – thirteen thousand kilometers to the wintering grounds. That requires a whole lot of calories.

Stilt Sandpipers in a farm field, Barnet, Vermont

Other birders found a group of gulls at Moore Dam, on the Connecticut River on the state line between New Hampshire and Vermont. I have visited the spot many times in the last few years, with almost no result. The Moore Reservoir just doesn’t seem to do much for avian wildlife. My suspicion is that the water level is yanked up and down to satisfy hydroelectric power demand, and this wreaks havoc with the aquatic food chain. Industrial pollution from past mill operations is also a factor. Ducks and loons just can’t find much to sustain them. Gulls have been few and far between. But in late August, a small group of gulls found their way to the dam, perching on those red buoys guarding the dam structures. The birders found the usual Ring-billed Gulls and Herring Gulls, but also a few Great Black-backed Gulls. The last of these is mostly coastal in distribution, but also makes use of the Great Lakes in winter, and sometimes the Connecticut River farther south. A sharp-eyed observer found that one of the larger gulls didn’t quite fit the pattern, and called out a Lesser Black-backed Gull among them – a coastal bird for sure. That drew another birder, who noticed a small, brown-colored bird in the flock that proved to be a juvenile Laughing Gull. Another coastal species. Yet another birder noticed a tern, which proved to be a juvenile Forster’s Tern. This one uses the interior of the continent routinely, but is rare this far north. These birds were joined by one juvenile Bonaparte’s Gull, an uncommon visitor to the area.

Laughing Gull, out of place at Moore Dam in New Hampshire

What was going on here? A few days prior to the gulls’ appearance, Hurricane Debby pushed through the southeastern US. (It hit South Carolina in the first week of August.) Storms have a way of stirring things up for birds. High winds will push a few of them northward. Some of the birds, especially juveniles with no experience, will drift inland. When the winds dissipate, the birds will find some suitable patch of habitat to land on. In this case, the Moore Reservoir on the Connecticut River was the draw. I observed this flock for several hours spaced across a few weeks of time, and I almost never saw them feeding successfully. They perceived the large body of water to be appropriate, but (being mostly juveniles) they did not recognize that there was very little food there. They eventually shipped out and likely joined their compatriots in better parts to the south. Opportunism drove them to make use of Moore Reservoir, but it was a short-lived impulse.

The ultimate example of opportunistic use of “habitat” must be an example from the northeastern US. Dairy farms generate a lot of manure, which is collected and processed for spreading on hay and corn fields. Manure is initially stored in an open pit, where it becomes a breeding ground for insects. Passing shorebirds take notice. In Vermont, a few of these pits become some of the best places to find shorebirds, since natural mudflats are almost impossible to find. This fall, I found a juvenile Baird’s Sandpiper at a pit near Hardwick. There were large numbers of Least, Semipalmated, Solitary, Spotted Sandpipers, and Killdeer at the same spot. Birding at a manure pit makes birding at a sewage plant seem positively fragrant.

Baird's Sandpiper, at a manure pit near Hardwick, Vermont

Clearly, patches of habitat are needed by migrant birds moving long distances in August, September, and October. What can humans do to help? First of all, we need to care for our wetlands. We have been altering them for human uses and human convenience for centuries. Many wetlands – thousands of square miles worth – have been altogether destroyed. Many have been modified in a quest to reduce mosquito-borne malaria. Many midwestern wetlands have been filled in to grow crops. Although it is hard to quantify, these actions have certainly resulted in population reductions for birds amounting to millions, and perhaps a billion. The modern form of ecological science has begun to quantify the damage, but much of the loss cannot easily be reversed without economic disruption to coastal city populations of people like you and me.

Second, we need to improve the way we manage the wetlands that still remain. Water levels can theoretically be managed carefully to sustain mudflats. This is true for both private and public lands. Reservoirs are mostly managed by the Army Corps of Engineers and the Bureau of Reclamation. Both have dreadful histories of monitoring wildlife populations on and near reservoirs and in the rivers they are situated on. The agencies comply with the Endangered Species Act, but just barely, and often only under pressure from conservation group lawsuits. Many hydroelectric dams in the east, like Moore Dam, are privately owned, and conservation goals are not valued highly.

One might expect better performance from the US Fish and Wildlife Service, which operates National Wildlife Refuges. Indeed, many NWRs today contain some of the best habitat in the country for waterfowl. But there are still problems. NWR managers normally feel that their mandate is restricted to ducks and geese, which generate significant revenue through hunting. Water in NWRs is managed to optimize duck habitat, but this doesn’t always work for shorebirds. Production of mudflats requires attention to the timing and amounts of water in impoundments. The showpiece for shorebird management is the legendary Bombay Hook NWR in Delaware. (The odd name seems to come from a dark chapter in its history, when the wetland was used to train bomber pilots for World War II combat.)

Scanning for shorebirds at Bombay Hook NWR, Delaware

Congress really needs to act to change the USFWS mission to enhance and preserve shorebird habitat on all refuges, even if waterfowl habitat suffers a bit. Congress should also force private dam owners to examine their impacts on wildlife. They operate at the behest of the people on whose land they occupy, so corporate goals should not be allowed to trump the public interest.

A mass of shorebirds at Bombay Hook NWR, Delaware, May 2024. Dunlins, Semipalmated Sandpipers, Short-billed Dowitchers, Semipalmated Plovers, and Black-bellied Plovers.