How do birds know when winter is coming?

Many bird species migrate when winter is coming. They are called migratory birds. They migrate to locations near and far to find food, to find nesting grounds, to return to breeding colonies, to find new places if their habitat is damaged or destroyed, to escape predators, or for other reasons. 

The birds that do not migrate are called residential birds. They stay in the same location and prepare themselves for winter. 

Birds need to know when winter is coming so that they can start their migration, protect themselves from winter storms, start hoarding food for the coming winter, or fluff-up their feathers to protect themselves from the winter chill. 

Birds know in advance when winter is coming. 

One way of detecting when winter is coming is the changing length of daylight hours. There are 24 hours in each day, and the amount of daylight hours in summer and winter varies due to the Earth’s orbit around the sun. In summer, there are longer daylight hours – up to 18 hours of daylight per day – whereas in winter, some locations have much less daylight hours – on average about 6.5 hours. The duration of daylight hours changes gradually and slowly, and birds, and other animals, can detect the changes. 

Scientists from Canada’s University of Western Ontario, Advanced Facility for Avian Research (AFAR), say that birds can sense slight changes in air pressure and changes in temperatures. 

They don’t know exactly how, but in 2019 they tested different possible reasons in their laboratory’s hypobaric climate wind tunnel for bird flight. They turned the air pressure up and down and watched the physiology and aerodynamics of birds in flight at different altitudes. Most of their work was with various Sparrow species. 

The scientists noted that the birds had two choices, depending upon the species and whether they were migratory or residential. The two choices were: 1) get out of the cold location, or 2) hunker down and protect yourself from the cold. 

Scientiist also think that birds may react to infra-sound, or sound at a frequency too low for humans to hear. Low-frequency sounds travel a long way, and one theory is that birds are hearing far-off thunder many hours in advance. 

Photographer: Martina Nicolls

Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM