Just as we humans follow environmental signals like calendars, clocks & weather to go through our daily lives and carry out various activities, plants and animals respond to cues from the changing seasons by altering their physiology and/or behaviors to enter new phases of their lives. These cyclical changes are driven primarily by the availability of resources, especially of food, which varies with prolonged changes in temperature, daylight, air pressure, & humidity, or in other words, seasons. For example, cooler temperatures and shorter days of autumn make deciduous trees/shrubs lose their leaves & go dormant. It also signals to some animals such as birds & bats to migrate to warmer areas. Those animal species, from mammals to insects, that cannot migrate and must stay put have other ways to cope with lack of resources and unfavorable environmental conditions. They enter periods of dormancy in which their metabolic rate, heart rate, & respiratory rate are all reduced to help them cope with lack of resources and survive food scarcity and/or extreme weather conditions of different seasons. This seasonal dormancy among animals is also based on their geographic location – hibernation (winter dormancy), estivation (summer dormancy), torpor (brief periods of inactivity), diapause (suspended development), brumation, etc. Warmer spring temperatures rouse hibernating animals and plants from winter dormancy to start a new cycle of growth and reproduction with more abundant/easily available food supply. The timing of the biological events of plants and animals in relation to changes in season is known as phenology. Wherever we might be located on this planet, these phenological events offer a unique opportunity to learn about, appreciate, and protect local biodiversity just as we enjoy changing seasons.
Here in the northern hemisphere, it is springtime now! We see two striking and connected??phenological events – deciduous trees leafing out and birds migrating northwards from their wintering locations near the south of the equator. Birds migrate mainly in response to the seasonal changes in the availability of the food wand water resources they need to survive and nesting locations to reproduce.
Different terrestrial and aquatic birds migrate at different times of the day along different routes. Bigger birds (e.g. cranes and pelicans), raptors (hawks and falcons), and those that can feed on the wing (e.g. swifts and swallows) migrate during daytime while smaller birds (e.g. songbirds like warblers and thrushes) make their journey at night thus avoiding predators. Here are pictures of sandhill cranes migrating through Chicago suburbs close to Lake Michigan:
Image source: https://www.allaboutbirds.org/guide/Sandhill_Crane/maps-range
In the North American continent, birds migrate along four broad corridors – “avian superhighways” – the Atlantic, Mississippi, Central, and Pacific Flyways.
During spring migration, billions of birds fly staggering distances over land and water to reach their breeding habitats in northern latitudes. Some trans-Atlantic seafaring (pelagic) birds like petrels and shearwaters cross the open waters of the Atlantic Ocean from Europe and Africa and fly along the Atlantic coast to reach breeding grounds in the Canadian Arctic.
Some individual species have been tracked via radio telemetry tags and the data they revealed are staggering. Here are examples of migration ranges of some North American birds:
Map & inset image source: http://www.swallow-tailedkites.org/2020/05/
Images source: https://www.boem.gov/sites/default/files/documents/renewable-energy/state-activities/USFWS-Migratory-Birds-Randy-Wilson_0.pdf
I saved the best (longest distance) migrant bird for the last – the bar-tailed godwit! The pictures say it all!
I promised to treat myself to infra-red birding equipment to watch these migrants when they head south in autumn! In the meantime, I will watch the diurnal migrants. Below is a live migration national map:
and the national migration forecast map for today:
The safety and survival of these millions of migratory birds depends on each and every one of us. Just as we take responsibility of protecting and providing for our loved ones including our pets, and take pride and ownership of our possessions, let us extending these sentiments to the wild creatures that share our space. Let us take ownership of their wellbeing and help these tired avian migrants during their incredibly long journeys by: keeping cats and other pets indoors to prevent their predation, by reducing outdoor lighting and putting decals (even simple strips of newspaper) on glass windows and doors to reduce their accidental collisions, and by providing them food, water, shelter, nesting material and nest boxes.
We can contribute to our collective knowledge of migratory birds by taking pictures of our sightings and sharing them on citizen science sites such as Journey North where we can also report other phenological events.
Citizen science apps such as eBird, and iNaturalist can help identify the birds. Learn more about bird migration here: https://www.allaboutbirds.org/news/the-basics-how-why-and-where-of-bird-migration/
In a nutshell the changing seasons play a vital role in the biology and behavior of plants and animals, including their cyclical changes, migration patterns, and dormancy periods. Phenology is the timing of these events in relation to seasonal changes. Springtime in the northern hemisphere is marked by the leafing out of deciduous trees and the migration of birds towards their breeding habitats in northern latitudes. Bird migration is a staggering feat of endurance, with billions of birds flying long distances over land and water to reach their destination. As responsible humans, it is our duty to protect and provide for these birds during their migrations, including keeping pets indoors, reducing outdoor lighting, and placing decals to prevent collisions with windows. By appreciating and protecting the phenological events of our local biodiversity, we can help preserve the natural world for generations to come.
1 https://birdcast.info/ BirdCast provides tools to predict and monitor bird migration that “predict how much, where and when bird migration will occur, live bird migration maps that show how much, where, and when migration is occurring in real-time, migration alerts to which one can subscribe to learn when intense bird migration will occur, and a dashboard that provides radar-based measurements of nocturnal bird migration at county and state levels in the contiguous US.”
