Fall brings football and the World Series. Pumpkin patches. Crisp fresh air. Brilliantly colored leaves are impressive. Yard and garden clean up. But I think, migrating birds are Autumn's real signature event. Do not you? Think about it for a moment. You may have to travel to find autumn foliage, a pumpkin patch or a football game.
But I'm sure you can find a spot to observe migrating birds near where you live, if not right in your backyard. Every autumn, more than 5 BILLION birds migrate across North America, crossing the US and Canada at rates of tens of millions a day. Now those are some serious numbers. So, lets get on with the migration talk and experience. It's late September / early October … Do you know where your birds are?
People have been fascinated with this annual migration of birds for thousands of years. The great Aristotle wrote about the wintering habits of birds 3,000 years ago. He noticed that some birds traveled to warmer places to spend the winter. He also mistakenly believed that some birds like swallows hibernated to survive the harsh winter weather. This theory persisted for 2,000 years! As you know, not all of your birds migrate. Some birds stay where they are. Scrub jays, Northern cardinals and Chickadees are an example of local and native birds that stay year round. Some birds have irruption years where they show in great numbers. Last year was an irruption year for Common redpolls and Red breasted nuthatches.
Birds that traveled several hundred miles to find a source of food. These birds were popping up in many regions where they normally are not seen. Not true migrating birds, but birds that move around some years are the Bush tits of the Pacific coast region. You may have other birds in your area that do not really migrate, but move around some (within a couple hundred miles) as they follow the food sources. Some birds, while not a migratory bird, become almost as intelopers. Vagabonds as they wonder around from place to place. Cedar waxwings fit this bill. Often small and even large flocks of waxwings will appear from no where. They strip your berry and fruit trees, never to be seen again for the rest of the season. Some times they gorge themselves into a drunken stupor on fermented fruits and fall off the branches they are clinging to. Novice birders may think their American goldfinches have migrated. When, before their eyes the Male goldfinch has moulted from his brilliant breeding yellow and black cap, to a dull olive green. You will discover, they never left. But, American goldfinches can and in some locations do migrate short distances some years 100 to 200 miles. However, a recorded migration of a single, banded goldfinch in Ontario, Canada, ended up in Louisiana, USA.
A typical Goldfinch migration may consist of your birds moving a 100 miles, but they are replaced by more northern goldies a week or two later. So much for hard and fast rules of migration. Then again … Many of us get fall and winter visitors like White crowned sparrows and American tree sparrows. Birds from northern Canada that winter over in our backyards or at least visit us on the way to their winter homes in the mid to southern United States. Other Northern birds like Dark eyed juncos and Snow buntings become winter favorites or a sign of Winter's coming when you see your first junco. Many birds do not bother to migrate until December or stay put in a mild winter. While some birds begin fall or summer migration as early as July and August, October is the big month for migration. Day light grows shorter each day.
Time clocks are ticking. Something inside tells billions of birds to fatten up. But the weather is still nice and there is plenty of food, why must they go now? Or it could be … It is snowing and blowing, why are you silly birds still here? Contrary to popular belief, birds migrate not because the weather becomes too cold, but because food supplies will run out. With the coming of winter, insect life dies down, snow covers the ground, water freezes over: Nature's cupboard is becoming bare. Birds that can find something to eat will frequently stay put, such as city pigeons or carrion-eating crows. Many robins remain in the North country as long as there is food enough for them to survive. Many birds change diet habits from fruits and insects to fruits and seeds or seeds and insect eggs etc. Some birds we are familiar with, like our beloved hummingbirds. You know what they feed on.
You may keep records of the day you first see one and when the last one leaves. Daylight hours dictate over 95% of departure time, though weather conditions can add on to or take away from departure time. For instance, On average my hummingbirds stay till September 24th / 25th. I still have plenty of flowers in bloom and the weather is still warm enough to provides insects. Yet, some years are unusually cool and an early frost may come before departure time. If the cool temperatures persist, they will leave early because food supplies are lacking.
When the weather is unusually warm, the might, just might hang around a few more days. This is more typical juvenile that has not gone through the rigors of migration. This is also why you want to keep your feeders out a couple of weeks longer. Three years ago, I had hummers into the second week of October. Unusual? Yes, but it does happen. Often these birds leave within the same week every year and return with in the same time frame in the Spring. Without a warning or a simple good-by, they are gone. Like clock work, swallows come and go. Get while the getting is good. Weather conditions are favorable, food sources are plentiful. What are they waiting for. Many species of birds congregate in fields, marshes, lakes, ponds and other areas waiting. These areas are known as staging areas. Adding body fat and waiting for cool nights and possibly a northerly wind to aid in southerly migration. Some birds are loners (hummingbirds) and head out on there own. While many of our migrating birds travel at night to avoid predators, some birds travel during the day. The day migrants include some of the ducks and geese, loons, cranes, gulls, pelicans, hawks, swallows, nighthawks, and swifts. Soaring birds, including Broad-winged Hawks, storks, and vultures, can only migrate during the day because their mode of flight makes them dependent on updrafts created either by thermal convection or the deflection of wind by topographic features like hills and mountain ridges.
Swifts and swallows feed entirely on flying insects, and circling flocks of these species are frequently seen in late summer feeding as they travel gradually southward. Catching your meal on the fly so to speak. Similarly, large flocks of Franklin's Gulls in the Great Plains feed on insects caught in thermals. Using these updrafts as a source of food as well as the means permitting soaring flight that carries them on their journey with minimal expenditure of muscle power. Large flocks of Swainson's Hawks also migrate in the Plains States by thermal soaring. In the East, flights of Broad-winged, Cooper's, and Sharp-shinned hawks are regularly seen along the Appalachian ridges, soaring on the uplifted westerlies passing over the crest of the mountains. Because many species of wading and swimming birds are able to feed at all hours, they migrate either by day or night. Some diving birds, including ducks that submerge when in danger, often travel over water by day and over land at night. Strong flyers like Snow Geese can make the entire trip from their staging area in James Bay, Canada to the wintering grounds on the Louisiana Gulf coast in one continuous flight. Snow geese have been recorded leaving James Bay and arriving on the Gulf of Mexico coast 60 hours later after a non stop flight of 60 hours and over 1,700 miles at an average speed of 28 miles an hour.
Try that on a tank of gas. Because most birds are creatures of daylight, it seems remarkable that many should select the night for extended travel. Smaller birds like rails, flycatchers, orioles, most of the sparrows, the warblers, vireos, and thrushes are typical nocturnal migrants. It is common to find woods and fields on one day almost barren of bird life an on the following morning filled with newly arrived migrants that came during the night and may spend several days as they re-fuel their fat supplies. Around me, marshes and wetlands are filling up with Red-winged-blackbirds as they are on countdown. Often I see and hear flocks of waterfowl during the night and I can hear other avian friends flying over head. Observations made with telescopes focused on the full moon have shown processions of birds, and one observer estimated their passage over his area at the rate of 9,000 per hour. This gives some indication of the numbers of birds in the air at night during migratory peaks. Radar observations have shown that nocturnal migration begins about an hour after sundown, reaches a maximum shortly before midnight, and then gradually declines until daybreak. Bird echoes during peak migration periods may cover a radar screen. It is suggested that small birds migrate by night to avoid their enemies.
To a certain extent this may be true because the group includes not only weak flyers, but also the small insectivorous birds, such as wrens, small woodland flycatchers, and other species that habitually live more or less in concealment. These birds are probably much safer making their flights under the protecting cloak of darkness. Nevertheless, it must be remembered that night migrants also include sandpipers and plovers. Most shorebirds are usually found in the open and are among the most powerful flyers, as some of them make annual nonstop migratory flights over 2,000 miles of open ocean. Night travel is probably the best for the majority of birds chiefly from the standpoint of feeding. Digestion is very rapid in birds, and yet the stomach of birds killed during the day almost always contains food. To replace the energy required for long flight, it is essential that either food be obtained at comparatively short intervals, or stores of fat be laid on prior to migration. If the smaller migrants were to make protracted flights by day, they would arrive at their destination at nightfall almost exhausted. Since they are entirely daylight feeders, they would be unable to obtain food until the following morning. The inability to feed would delay further flights and result in great exhaustion or possibly even death should their evening arrival coincide with cold or stormy weather. By traveling at night, they can pause at sunrise and devote the entire period of daylight to alternate feeding and resting.
This schedule permits complete recuperation and resumption of the journey on a subsequent evening after sufficient fat deposits have been restored. Banding studies have shown that the number of days an individual lays over during a migration stop is inversely dependent upon the amount of its fat stores upon arrival and weather conditions. It has also been hypothesized that nighttime migration is advantageous because environmental temperatures are typically cooler. The effort involved in migratory flight generates considerable heat. The primary way in which flying birds loose heat in order to maintain an optimum body temperature is through the evaporation of water from air sacs that are part of its breathing system. Indeed, dehydration resulting from regulation of body temperature rather than the amount of fat stores probably limits the distance a bird can fly nonstop. Thus, by flying in cooler air, which increases heat loss by conduction and convection, less cooling by evaporation of limited body water is required and flight distances are extended. These marvelous, feathered, flying machines are to close to perfect. Our Creator's nature is a marvel to behold and we should be in AWE of his works. Even when they do not stay year round for us to enjoy. Be sure to read parts 2 and 3 on migration.