(Note: This meeting and presentation took place online, via Zoom, due to social distancing protocols prompted by the ongoing COVID-19 pandemic.)
At 7:00 pm, President Rochelle Thomas called the meeting of the Society to order. After welcoming the meeting attendees, she reminded members of the upcoming beach cleanup at Cedar Grove in Staten Island. President Thomas also noted that members who have yet to pay their dues could do so online or via mail.
Motion 1: President Thomas announced the results of the online new-member vote, which passed with 146 votes of approval and 0 of disapproval.
The Society welcomed the following eight new members:
- Annie Wilker, Active Member, sponsored by Miriam Rakowski, Evelyn Huang
- Sarah Lisciandro, Associate Member, sponsored by Asta Skocir
- Paul Bovitz, Active Member, sponsored by Lenore Swenson
- Hannah Cui, Active Member, sponsored by Ronnie Almonte
- Aris Concepcion, Active Member, sponsored by Sylvia Alexander
- Ho Kei (Heidi) Ng, Active Member, sponsored by Amanda Bielskas
- Marie Cohen, Active Member, sponsored by Leslie Fiske
- Paul Cohen, Active Member, sponsored by Leslie Fiske
Motion 2: President Thomas then announced the result of the online vote to approve the minutes of the September 2022 members meeting. The vote passed with 144 votes of approval and two abstentions. The final copy has been updated with member suggestions.
At 7:03 pm, President Thomas introduced the evening’s speaker, Roger Pasquier.
Roger Pasquier is an associate in the Department of Ornithology at the American Museum of Natural History. A member of The Linnaean Society of New York since 1968, his career has been in ornithology and conservation at the American Museum of Natural History, the U.S. National Museum, the World Wildlife Fund-U.S., the Environmental Defense Fund, and the National Audubon Society.
Birds in Winter: Surviving the Most Challenging Season
Effects of Winter
Winter affects about a third of all the world’s bird species. The season is colder, windier, and much longer than the breeding season. Birds must survive with less food, light, and time for foraging, in addition to longer nights. During this time, some birds stay put, but many others migrate south. In the Western Hemisphere, birds migrate to a winter range that is much smaller than their summer range, which leads to increased competition for resources. Southern migration typically brings the additional challenge of more predators and resident species on the winter range.
Types of Migration
There are many types of migrations, including partial migration, where some of the population moves from an area while others remain. Some migrations are short-distance, typically a few hundred miles, while on long-distance migrations, birds travel much farther, usually to a tropical zone or beyond. Altitudinal migration occurs in the Appalachians and, more commonly, in the Rockies.
Non-Migrating Species
Feeders
Many people are interested in the impact of feeders. For chickadees, feeders have little effect. However, feeders can be essential for species like the Carolina Wren, for whom one peanut is a third of the daily metabolic need.
Scatter Hoarders
Chickadees cache food using a scatter-hoarding technique. They store different foods in various well concealed locations for later retrieval, often weeks or months later. Every fall, the chickadee’s hippocampus (the part of the brain dealing with memory) expands to contain the many locations of the hidden food and then contracts again at the end of the winter. Blue Jays store a wide variety of acorns; one of the ways oaks increase their range is by germinating from the acorns that the jays have never retrieved. Red-bellied Woodpeckers hide fruits such as crabapple, apple, or cherries in the deep grooves of the bark of locust trees. White-breasted Nuthatches store seeds and other little bits, usually in cracks in tree bark, sometimes in the ground.
Larder Hoarders
Owls and kestrels are examples of larder hoarders. These birds have a single cache to store food after they catch and kill it. These hoards are usually temporary, as the food would decompose if left for a long time.
Short-Distance Migrants
Distribution
The Dark-eyed Junco displays a variety of migration patterns based on latitude, age, and gender. Generally, the adult males winter farther north than the females and younger birds. However, some young males winter even farther north than adult males, ostensibly to reach desirable breeding territories before the adult males arrive.
Eruptions
Everyone’s favorite erupting species is the Snowy Owl. Recently it has been determined that these eruptions occur when food has been particularly abundant during the previous breeding season, resulting in a higher number of young birds. This population increase causes food scarcity in the usual range and necessitates a wider dispersal of birds during the winter.
Long-Distance Migrants
There are 40 species of warblers that migrate into the narrow range of the Caribbean Islands, parts of Mexico, and down through Colombia. A few, such as the Blackpoll Warbler, go even farther.
Non-Overlapping Territories
Some of these species share breeding ranges but have discrete winter ranges that are non-overlapping. During the spring and summer, the Bay-breasted Warbler and the Cape May Warbler reside in a vast and almost entirely overlapping range in the boreal forest, while they winter in completely different locations—the Bay-breasted in mainland Panama and Costa Rica, and the Cape May in the Caribbean Islands.
Overlapping Territories
A lot of these warblers have overlapping winter ranges. For example, 18 warbler species spend the winter in Jamaica, and another twelve migrate through. During the breeding session, the Louisiana Waterthrush favors running water, while the Northern Waterthrush favors still water and boggy areas. Where they overlap in winter, they stick to those same habitat choices. The Black-and-white Warbler feeds entirely on the bark of trees, so it doesn’t care what other warblers are around during the winter. The Worm-eating Warbler has a specialized winter diet that it accesses by probing into curled-up dead leaves and flowers.
Species Hierarchy
Some birds in overlapping areas practice domination over other species. For example, the Yellow Warbler is dominant over the Magnolia Warbler. Others have hierarchies within their species, such as the male redstart, which in the Caribbean inhabits the bug-rich mangroves and wet areas, while female and young redstarts use the the scrub and drier habitats.
Habitat Specialists
Other warblers, such as the Kentucky, are habitat specialists who spend the winter in the deep forest. The Chestnut-sided Warbler stays at the forest edges. The Tennessee Warbler moves around and has a flexible territory.
Territory Sequence
There are a few North American birds that winter in the tropics using a sequence of territories. Veeries move around the Amazon basin, looking for unflooded areas. The Purple Martin has a three-part migration: some go to Colombia, some to Amazonian Brazil, and others farther south to Bolivia—a tactic to avoid overcrowding, it is thought.
Migratory Connectivity
All Wood Thrushes display migratory connectivity, meaning that birds from a particular breeding region also stay grouped together on their wintering grounds. This creates a conservation imperative to preserve the habitat in both locations.
Territorial Hierarchy
The Yellow Warbler is a long-distance migrant with wintering territory across Mexico. Males have been observed driving away as many as 29 other species. Male yellow warblers inhabit the canopy while the females remain in the understory, indicating that there is territoriality and hierarchy not only among species, but also within species.
Floaters
There are floaters, such as Wood Thrushes, who never establish a winter territory but drift around the margins of other species’ territories. These birds have far lower over-winter survival rates than those that maintain territories.
Flocks
Some species spend the winter in flocks, which provides safety in numbers. Flocking species often feed from fruit trees that are not easily defended, or in locations where the food is very patchy. Since this requires them to move around, they have no need to defend a territory.
Aerial Migration
Another reason some birds stay in place is that roosting sites are scarce. Some shorebirds spread out at low tide while feeding and form flocks in the air at high tide. Sanderlings, Dunlins, and other sandpiper species spend the hours of high tide flying over the sea in what is called aerial migration. This behavior lessens the danger of being caught by a predator.
Competition
It is unclear how much competition there is between North American over-winterers and resident birds of the tropics. A study in Venezuela, where North American migrants coexist with tropical resident birds, showed that the smaller resident Turkey Vulture retreated when North American vultures were present, conceding the more open areas to the migrants. When the migrants left, the resident vultures returned for their breeding season. Among migrating warblers and resident insect-eating birds in the tropics, most migrant birds take smaller prey, work harder to find the prey, and are often still feeding when the resident birds have finished and are taking shelter. They also tend to eat ants and beetles that the residents find distasteful.
Survival
During the winter, finding food and avoiding predators are the primary activities that occupy birds. Warblers who winter in the tropics have a 90% survival rate, much higher than for those who do not migrate.
Shifting Diets
Many migratory species shift their diets on their winter grounds. Kingbirds become specialists in one type of tree, and they follow it from Bolivia all the way through Colombia and then into Panama at the exact time when it comes into full fruit. The kingbirds devour the fruit, disseminate the seeds, and move on to the next crop. Among birds that don’t winter so far south, the Yellow-rumped Warbler and the Tree Swallow shift their diets from insects to Bayberry.
Acclimation
Another way that birds survive the winter is by acclimation rather than migration. For example, Snowy Owls have feathers down to the tips of their toes. Smaller birds can fluff their feathers, trapping air to keep them warm. Most birds eat more at the end of the day, when they need fuel to carry them through the long and cold winter night. Some birds adjust their behavior during the day. For example, chickadees move more slowly and go to roost earlier in extremely cold weather to save energy.
Roosting Habitats
Roosting habits also change during the winter. Ruffed Grouse roost in snow burrows, as do many small birds, including Snow Buntings, redpolls, and wrens. They use high-velocity flight to project their bodies into the soft snow, which then collapses into the hole behind them, thereby leaving no visible entrance for a predator to find. The birds work their way back out of the snow in the morning, sometimes using a different exit. Other birds roost in cavities that keep them warm and protected from predators. Many birds roost in groups during the winter, further insulating them. Bluebirds often group together, and as many as 89 Winter Wrens have been found occupying a single cavity.
Hypothermia
Some birds use hypothermia to survive the cold. For example, chickadees automatically drop their temperature at night by about 10 degrees Celsius to reduce their internal fuel consumption. Hummingbirds and sunbirds do this during the day at high latitudes in the summertime. The whip-poor-will can sleep for several days without moving and without feeding. It is suspected that other nightjars may also do this, but nothing conclusive has been found.
Conservation
HIPPOIt is essential to understand which seasons and locations impact the survival and reproduction of bird populations. To support this, E.O. Wilson devised the conservation acronym HIPPO, which stands for Habitat, Invasives, Pollution, Population, and Overharvest.
Habitat LossIt is well known that the Bachmann’s Warbler became extinct because its wintering habitats in Cuba and the Isle of Pines were completely lost during the 20th century. The near-threatened Piping Plover is difficult to protect because we do not have a clear understanding of its wintering habitat.
Modified Habitats
We do know that some birds can adapt to modified habitats. For example, the Cerulean Warbler does very well wintering in the shade trees planted at Colombian coffee farms. Unlike coffee trees, these trees provide enough insects for the Cerulean Warbler without displacing the resident birds. This strategy might also be better for the resident birds, but at the moment the focus is on increasing the wintering habitat for migrants.
Invasive Species
There are many invasive plants and animals that threaten birds, but one of the most challenging is cats that spend time outside. In the US alone, cats kill one to four billion birds annually—more than pesticides, collisions with buildings, or other causes. Cats are highlighted as a winter problem because birds tend to stay in suburbanized and cat-filled areas due to feeders.
Pollution
Pollution is global, but a good example of how it directly influences bird species is the case of the Whooping Cranes that winter in the Texas Gulf Coast. Unlike their pristine Canadian breeding habitat, the southern wetlands are contaminated with effluent from the surrounding areas, including pesticides, herbicides, petroleum, hydrocarbons, heavy metals, and industrial pollutants.
Population
Human population poses a threat during the winter because humans occupy winter breeding grounds, especially beaches and mountain resorts where people are vacationing.
Overharvest
While most people think waterfowl hunting is fairly well regulated, there is a particular problem in the length of the season. By the last months of the hunting season, in January and February, birds are already paired for breeding; if one of the pair is killed, there is often not enough time for the surviving bird to find another mate. The more serious problem of overharvesting is that seabirds are often caught in long fishing lines and gill nets that run for miles in the winter, when more birds are out in the open ocean.
Climate Change
Climate change is another form of pollution that exacerbates all other aspects of HIPPO. Impacts on habitats include sea level rise, which reduces coastal wintering areas; snow cover contraction, where precipitation decreases in subtropical zones and increases in high latitudes, causing prolonged and intense droughts; and severe storms stretching farther north.
Wintering Habitats
A good example of a change in wintering range is provided by the American Robin, which used to be considered a harbinger of spring. These birds now live here throughout the year because there’s less snow and less reason to migrate. Many other birds are also spending less time on their wintering range. Golden Eagles in Michigan and Minnesota have been observed arriving up to a month earlier than historically documented.
Physical Adaptations
In addition to behavioral adaptations, scientists are also seeing physical adaptations to the changing climate. In the last few decades, warblers have had an average weight that is less than it used to be. This is in response to the warmer environments in which they live; smaller birds dissipate heat faster than larger ones.
Phenological Disjunct
Because spring is coming earlier, birds that winter in the tropics are starting to migrate north earlier. Trees are leafing earlier, and insects that feed on those trees emerge sooner. The European Pied Flycatcher, which winters in Africa south of the Sahara, is now having trouble when it arrives at its breeding grounds: by the time it gets there, resident birds have already consumed the caterpillars it typically eats in the spring, leading to poor breeding productivity and population decline. Canada Jays store food during the winter because when they begin nesting in late winter, there is little food available to feed their young. Recent winters have been so warm, however, that the food caches are rotting, resulting in a lack of food for their young at the end of winter and in early spring.The evening ended with officers of the Linnaean Society thanking Mr. Pasquier for sharing his fascinating knowledge about birds surviving winter.