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December 2020

Vol. 48, No. 6

About Books: Birds During the Annual Occupation

Mark Lynch

Birds in Winter: Surviving the Most Challenging Season. Roger F. Pasquier. 2019. Princeton, New Jersey: Princeton University Press.

“Winter is not a season, it’s an occupation.” (Sinclair Lewis)

Although I am writing this in early October, winter is looming on the horizon. Birdsong has almost ceased. Many migrant species are heading south in mixed species flocks. Resident species such as chickadees are forming their large winter flocks. Some local Blue Jays are caching food, while many other jays are migrating. Juncos and White-throated Sparrows are at the feeders. It looks like it will be a good winter for irruptive species such as Red-breasted Nuthatches, Purple Finches, and Pine Siskins. For some reason, Red Crossbills have been here for most of the summer. Waterfowl are just starting their migrations, and I expect to see an odd scoter on an inland lake any time now. Yes, there is still plenty of migration to be enjoyed, but I have already been birding while wearing my fleece, gloves, and winter hat, so the first snowflakes cannot be far behind.

Winter is tough on birders, particularly birders who live in the central and western areas of southern New England. Temperatures can dip well below freezing for days. Snow can pile up in feet, and treacherous ice is everywhere. Daylight hours get short, and so do our day lists of species. There will be an occasional interesting bird at a feeder, of course, but those are few and far between. Most of the birds we spot after the final freeze of the ponds and lakes are those hardy resident species. Along the coast, the birding prospects are brighter. There are loons, grebes, alcids, and flocks of waterfowl. Even land birding in southern coastal locations can offer some relief from the doldrums of birding in western Massachusetts locations. Southeastern coastal spots always have a few “half hardies” like towhees, catbirds, or Hermit Thrushes lingering in thickets. Finding a catbird in July is no big thing, but spotting a catbird in February in Massachusetts will give you a momentary thrill. And there is always the rare possibility of turning up something really interesting like a chat or a warbler that should have left months ago.

Birders may grouse about the cold, snow, and paucity of birds, but we can always retreat to a warm home, a shot of scotch, and a relaxing evening binge-watching a series on Netflix. If winter is tough on birders, it can often be a matter of life and death to the birds. Facing winter, birds can do two things: migrate—sometimes long distances—or remain in place and tough it out in weather conditions that can quickly turn deadly.

“Should I stay or should I go now?
If I go, there will be trouble
And if I stay it will be double” (The Clash)

Birds in Winter: Surviving the Most Challenging Season is a fine survey of what is currently known of how birds live through the Northern Hemisphere winter. Roger F. Pasquier is a lifelong birder who has worked with conservation organizations such as the International Council for Bird Conservation, the Environmental Defense Fund, and the National Audubon Society. He is currently an associate in the Department of Ornithology at the American Museum of Natural History. In Birds in Winter, Pasquier has brought together research from numerous field ornithologists around the world and has fashioned a concise overview of winter bird behavior.

Birds in Winter begins with a global overview of the major avian migration systems. These include the Nearctic/Neotropical (summering breeding birds fly from northern North America south to the Caribbean, Central and South America); the Palearctic/African (European birds migrate to south of the Sahara); the Palearctic/South Asian (eastern Eurasian Birds fly to southeast Asia); Austral South American (from south to northern areas of South America); Austral African (from southern Africa to more northern areas of Africa); and Australia and New Zealand (too complex to describe here).

Within each migration system there is a variety of types of migration. In partial migration, part of the population of a species migrates while others remain in place. Here in New England this may include species such as jays, crows, and chickadees. Typically, it is the more northern populations that most often move, sometimes leap-frogging over local sedentary populations. In short-distance migration, birds move, but not that far. New England populations of species such as catbirds and Hermit Thrushes move to the mid-Atlantic states, south to Florida and the Gulf. Long distance migration includes some of the most dramatic movements of bird species such as the Blackpoll, most shorebirds, and Arctic Terns. Sometimes it is difficult for birders to understand just how far these movements are. I did not really have a gut understanding about how long these distances are that the migrants fly until I saw a White-rumped Sandpiper on a rock with a sheathbill and penguins when I was on a pelagic in the Beagle Channel off Tierra del Fuego. I had complained mightily about the long flights that took me from Boston to Ushuaia, but here was a tiny shorebird that had flown from Alaska across two continents under its own steam to the southernmost tip of South America. Finally, pelagic species, like tubenoses, are a special case and exhibit a variety of migration behaviors: “Seabirds responses to winter are guided by ocean currents, water masses, and climactic zones.” (p. 28)

Besides these migration systems, there are irruptions, the occasional or periodic southward movements of species often due to food shortages or population increases on their typical wintering range. These include charismatic species such as Snowy and Great Gray owls, Rough-legged Hawks, and the so-called winter finches. These movements can vary dramatically in our area from winter to winter. Birders love irruptive species because they spice up winter birding. Some of these movements are periodic, while others are less predictable.

Invasions of some other irruptive species, however, from the insectivorous Golden-crowned Kinglet (Regulus satrapa) to the frugivorous Bohemian Waxwing (Bombycilla garrulus) and the bud-and-seed-eating Purple Finch (Haemorhous purpureus), do not correlate strongly to the movements of any other species. (p. 19)

Though many species exhibit winter site fidelity, returning to the same area year after year is a more fluid situation for some species. Even after a bird arrives on its wintering territory, severe weather conditions or lack of food availability may cause it to move once or twice again. This is called facultative migration.

Facultative migration, the decision a bird makes to move weeks after it has finished its normal autumn migration and reached a destination within the species usual winter range, may come irregularly, rather than annually, in response to unpredictable conditions during the severest part of an exceptional winter. (p. 20)

In central and western Massachusetts, we see facultative migration in species such as Hooded Merganser. These tough little ducks will hang around long after most other waterfowl have headed south or to the coast as long as there is a bit of open water along a river or pond. But as soon as the temperature gets too cold and all the water freezes, they will move south and coastwards.

Even in wintering areas where the weather is not expected to turn severe, some species may still have a series of sequential wintering sites.

About 44% of the Purple Martins (Progne subis) that spend the first part of the winter in central Amazonia, for an average of 66 days, then move a mean distance of 776 km south or east for another 77 days. Of the martins that move, 18% leave the second site after some days or weeks for a third destination for an average of another 763 km, where they remain some 58 days. (p. 76)

Migration is a lot more complex and varied than most birders understand. There is also “differential migration” (p. 66) in which birds of different ages or sexes within in a species migrate to different areas. In migratory birds of prey, females winter farther from their breeding areas than males. Some passerines also follow this pattern:

‘Differential migration’ has been most thoroughly studied in eastern populations of Dark-eyed Junco (Junco hyemalis). In northern New England and west through the Great Lakes region and beyond, 80% of wintering juncos are male. From South Carolina to the Gulf Coast and Texas, 70% of the birds are female. (p. 66)

For short distance migrants, what factors determine where they go? Basically, most species seek out areas that approximate where they bred except that the wintering location will not be as cold or snow-covered. Overwintering catbirds on the southeastern coastal plain of Massachusetts seek out thickets and brush similar to areas where they bred.

For most short-distance or partial migrants, the wintering site is not substantially different from the place they departed. Waterfowl winter on water bodies: fresh, estuarine, or coastal that do not freeze. They move to another if the initial site does freeze. Forest raptors stay in forests. Raptors of open country that take prey from the ground move to open country less likely to be covered with snow. Passerines that do not travel far similarly remain loyal to their breeding habitat, be it woodland, scrub, or grassland. Even as these change when trees become leafless, other vegetation dies back, and weather conditions alter so that some birds must shift to a different food source. (p. 53)

Preparing for winter, whether species are long- or short- distance migrants or even if they plan to overwinter in the area, begins in early fall. Passerine species that are insectivorous may switch their diet to berries and fruit.

Passerines are among the birds that see the greatest shift in diet before autumn migration. Those that feed themselves and their young protein-based animal matter often shift to fruits that provide fructose and lipids. This is easy to observe in late summer when many migrants gather at fruiting trees and shrubs. (p. 48)

Here in Massachusetts, we see this in species such as bluebirds, waxwings, and robins. During the breeding season, robins can be found on lawns listening for earthworms or tossing dead leaves looking for insects. Deep in winter, some populations of robins in Massachusetts become itinerant frugivores, searching for crab apples, bittersweet, sumac, and other fruit over wide areas, while at night they may form large communal roosts.

Birds that remain in place in northern climes face a different set of challenges. First and foremost is finding food. There is a lot less daylight, which means much less time to search for food. Some passerines in winter search for food most intensively in the morning, while others search at the end of the day. Small species such as chickadees, kinglets, and creepers are able to find sustenance in crevasses in bark, seed pods, or at feeders. They may form mixed species flocks that patrol an area daily in a never-ending search for food. Larger species may cache food. “Food storage takes two forms: scatter-hoarding, where food is put in many separate locations and larder hoarding, where it is kept together.” (p. 42)

Locally, Blue Jays are our most common species that scatter-hoard food, taking choice nuts and seeds from our feeders and flying to a number of locations to cache them. The best example of a larder hoarder is the Acorn Woodpecker, which caches numerous acorns in holes it drills in a dead tree or phone pole. Red-headed Woodpeckers are also larder hoarders. Some migratory raptors are hoarders, too.

In winter, most owls cache their food in larders rather than scattering it. They frequently decapitate, eviscerate, or eat some of each item before storing it.” (p. 46) If it is very cold, species such as Saw-whet Owls may have to thaw their cached prey a bit before devouring it by “assuming an incubating posture” on the mouse. (p. 47)

Is there greater mortality among long-distance migrants or among species that stay put for the winter in northern climes? The answer is complex.

The distinctive aspects of migratory and sedentary life cycles must be considered. Among woodland passerines, young of migratory species survive their first year half as well as adults, and young of sedentary species only one-quarter as well; the challenges of a cold winter where adult birds occupy the best sites may therefore be greater for inexperienced birds than two migrations and a season in a new environment (Sherry and Holmes, 1995). For some highly migratory birds of prey, mortality is most intense on migration, but these brief periods of the annual cycle are balanced by longer portions of the year in breeding and wintering areas; there, the per-day rates may be lower but the total seasonal rates of loss equal those experienced on migration. (p. 207)

Please realize that for this review, I am citing only a few of the findings found in Birds in Winter. The book is a wealth of information about migratory behavior and how birds survive winter, and it is impossible to summarize all the interesting information that can be found there in this short review. The bibliography is extensive, running from page 251 to page 283. It is impressive to note all of the articles, papers, and books Pasquier has referenced to write Birds in Winter. An added bonus is that this book is nicely illustrated with numerous black and white drawings by Margaret La Farge.

The final two chapters of Birds in Winter, “Conservation” (p. 207–32) and “Climate Change” (p. 233–50), end the book on an appropriately somber tone. It is not just weather or the rigors of a long migration that affect wintering birds. Pasquier uses the acronym HIPPO, created by Edward O. Wilson, to list the human-caused challenges winter birds also face, listed in order of impact:

Habitat loss

Invasive species

Pollution

Population growth

Over harvest (p. 207–8)

Pasquier devotes several subchapters to each of these ongoing problems. Wintering birds, already challenged by the season, are further pressured by these considerable and growing trends. Even protected species such as the Whooping Crane, wintering in coastal Texas, are feeding in waters that can be a toxic stew of agricultural runoff: “Pesticides, including fungicides, herbicides, insecticides, and rodenticides, as well as antibiotics, are all now known to have much greater effects on target species than was anticipated as these were developed.” (p. 219)

Species wintering along our coasts may face constant harassment by human use of the beaches they use to find food. “In California, where winters are mild and the human population is large, the disturbance to shorebirds on beaches may be constant. At two beaches near Monterey, Sanderlings (Calidris alba) were disturbed by people or their dogs once every 15 minutes on average. (p. 224)

Of course, all of these impacts on wintering birds are dwarfed by the ultimate challenge of global warming. We are already seeing the effects on certain species. Changing winter conditions due to climate change or increasing human habitation have altered certain species’ migration patterns and locations where they overwinter. This is most dramatically seen in two hummingbird species. Rufous Hummingbirds are now more common in winter around the Gulf and southern Atlantic coasts than they were 50 years ago. Now Ruby-throats are also showing up in these same areas in winter.

Still more recent is the expansion of wintering Ruby-throated Hummingbirds (Archilochus colubris) over much of the same area from their usual winter range of central Mexico to Panama. Climate change, which has accelerated since the earlier expansion of the Rufous Hummingbird, as well as the availability of flowering gardens and feeders, has likely enhanced overwinter survival. A banding study in South Carolina found more males, especially immature, than females, and the average return rate from one winter to the next was 19.4% (Cubie 2014). (p. 30)

The effects of global climate change on wintering bird behavior are still not obviously widespread, but certain red flags have already been noticed:

A comparison of 193 separate populations of migratory birds breeding in the Nearctic and Palearctic found that the Nearctic species most in decline between 1980 and 2006 were those with the greatest differences between the increase in the average temperatures in their breeding and wintering ranges, leading to migrants arriving later relative to the advance of spring. (p. 239)

Looking ahead, changes in rainfall and rising winter temperatures caused by climate change may also bring about serious declines in the breeding of certain species.

The breeding success of Kirtland’s Warblers is determined by the extent of rainfall in the Bahamas during March. Rainier years there put the males in better condition for migration and establishing territories. (p. 181)

Breeding success of Gray Jays has declined in Ontario where rising winter temperatures have caused some of the food the jays store to rot before they retrieve it. (p. 246)

Birds in Winter is a major achievement, a fine overview of many of the aspects of wintering bird behavior, a well-edited compilation of modern research. Birds in Winter gives the reader a better understanding about how birds prepare for migration, what occurs to them in migration, and how they survive in winter whether they are in the tropics or northern regions. There is a wealth of information in Birds in Winter. It is a book you can read straight through or use as a reference. This is a perfect book to crack open when you are finally safe inside after a long day out in the elements, chair near the fire, a warming beverage at hand. Reading Birds in Winter will make you pause to give a thought to how amazing it is that those tiny chickadees that visit your feeder survive through the season of ice and snow.

“That’s what winter is: an exercise in remembering how to still yourself then how to come pliantly back to life again.”
( Ali Smith , Winter )

NB: Roger F. Pasquier is the author of other books about ornithology and birds, and he has also written a stunning book on artists who have painted Central Park in New York City. Painting Central Park (2015. New York, New York: Vendome Press) is a sumptuous large format art book that even illustrates a stroll across the park entirely with works by major artists. Pasquier is a long-time passionate birder of Central Park, and he is an expert guide to the many painters who also have fallen in love with this jewel of a park.


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