As the wind starts blowing and the trees turn brown, it is common that we look up at the sky, notice some birds flying south in flocks, and realize that it is time for their migration. Have you ever wondered about the reason why they are migrating and their destinations? Isn't it marvelous that these feathered creatures would spend days or even months traveling to a new world to get ready for the winter? This article sets out to share knowledge of these questions and to lead bird lovers like you into a deeper understanding of our feathered geniuses.

bird migration

Why do birds migrate in the winter?

According to statistics, around 40% of all bird species on Earth are migratory. Despite the arduous nature of a migratory journey, countless birds of different types still continue to glide across continents as seasons change. Why? The answer is obvious and easy to guess, which lies in a mix of genetics and environmental factors. To be specific, birds need a more hospitable land to survive due to the decreasing resources in the winter season. The freezing weather in winter itself is unbearable for birds and has a huge impact on the natural vegetation around their habitats. Fewer food (insects, plants, etc.) and nesting choices are available for our poor winged friends, and they are more prone to be spotted by predators. To summarise, migratory birds' biological genes drive them to respond to the changing environment and to better survive the harsh times by moving to warmer climates.

What do birds rely on for migration?

After learning about the reasons that birds migrate, you may start to ask how they are capable of carrying out such complicated work and overcoming obstacles that would appear unachievable to us humans. The answers are as follows. First of all, it is generally believed that migratory birds have an internal clock that reminds them when it's time to migrate. Through the journey, they take advantage of their intrinsic sense which relates to the magnetic field on Earth, and use that for navigation. In addition to that, birds also leave trademarks and adjust their routes in response to the local temperature, geographic conditions, availability of food and shelter, day length and daylight, etc.

hospitable environment for birds

Do all birds migrate in the winter?

The answer is NO. Though migration seems a genius choice to escape the sharp weather, it is accompanied by risks and challenges such as distance and unpredictable predators along the journey. There are at least 10,000 bird species all around the world that settle in all sorts of habitats and vary in behaviors and sizes. To avoid the potential risks of migration, some of them may choose to settle down in an area.

Black-capped Chickadee

Birds that don't migrate tend to have a better gift for maintaining their body temperature and are more skilled in food caching. Some of them can even reach a state called torpor (mini-hibernation) that reduces their requirement of calories throughout the night. These traits help them tough it out during the winter season. Staying in the original regions enables these overwintering birds to save energy, and they can guard their territory without having to adjust themselves to a new surrounding through the winter as well as in the next spring.

Listed are a few permanent bird residents that do not migrate in the winter: Golden-crowned Kinglet in Alaska and Nova Scotia, Black-capped Chickadee, Northern Cardinal, Turkey, Quail, Black Vulture, and Hairy Woodpecker, Downy Woodpecker, Blue Jay, Robins, Blue Tits, Blackbirds.

Blue Tits

What parts of the world do birds go to in the winter?

The main parts of the world that birds migrate to are Southern Europe, the Mediterranean Region, Africa, the Middle East, Southeast Asia, New Zealand, Canada, and the southern part of America. And their main flyways are the Atlantic, Mississippi, and Pacific Ocean. The migratory journey can be divided into three types according to the overall traveling distance of birds:

1 Short-distance migration
Many species only travel a few miles, which includes moving from higher elevations to lower ones where it is warmer. This is known as Altitudinal Migration. Birds who do this include siskins, goldfinches, band-tailed pigeons, violet-green swallows in the UK, grebes in the Andes, buffleheads, ruffed grouse, tree sparrows, and cedar waxwings in North America, just to name a few.

2 Medium-distance migration
These bird species travel to a nearby region or state. Take the US as an example, 80% of the avian species fly to the central or southern part of the country, such as the Eastern Bluebird and Killdeer. Many waterfowl species will travel from northern Canada, and then downwards to southern states such as Texas and Louisiana.

3 Long-distance migration
The longest migration distance is from a small songbird called the Northern wheatear, who travels 13,000 miles to Africa in the winter. Other long distance travelers to Africa are swallows, cuckooa, willow warblers, and chiffchaffs of the UK. The blackpoll warblers, scarlet tanagers, Eastern bluebirds, orioles, tree swallows, eastern kingbirds, bobolinks, and chimney swifts prefer to winter in South America. Ruby-throated Hummingbirds move from North America to Central America, travelling a distance over 2,000 miles. European starlings from east Europe migrate towards the Atlantic coast. And California gulls who breed in Utah migrate westward to the Pacific coast to survive the season.

Where do migratory birds roost at night through their journey?

Rest is essential for migratory birds to save enough energy for the next day. The two basic factors that they require from a temporary shelter are warmth and safety. The main types of shelters are thick vegetation like hedges, dense foliage, tree hollows/cavities, snowdrifts, eaves, and man-made bird shelters like birdhouses, bird feeders, abandoned buildings, barns, chimneys, flues, etc. There is a rule called “safety in numbers”, which refers to the situation in which most birds flock together at night to ensure safety and maintain body temperatures.

man-made bird shelter

The role of human intervention in winter bird conservation

In addition to environmental factors, human influence also plays a crucial role in birds' winter migration. Human-induced climate change alters weather patterns and can affect the timing and availability of food for birds. Artificial light and tall buildings in cities can pose a significant threat to birds' navigation and even lead to injuries or fatalities. At the end of this article, it is worthy of stressing that we need to be aware of our role during this special period of our feathered friends and put in efforts to reduce human impact. Preparing bird food would be a good choice.
October 12, 2023 — Yin Liang

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