Migratory birds and mammals that waste a lot of energy to hunt for food or find a place to nest tend to live quickly and die young, scientists have reported.
In a study published in Nature Communications, researchers found that migratory animals have a shorter life than domestic members.
But they compensate for having more descendants in less time.
Examining more than 700 birds and 540 mammal species, the study determined that from one evolutionary point of view neither strategy is “better” than the other.
“These are just two different ways to solve life’s problems,” said Stuart Bearhop, a professor at the University of Exeter in the UK, the author of the study.
“One way is to live fast and die young, the other is to live slowly” and create offspring in a longer life.
It is balanced, otherwise one group – migratory or non-migratory species – would prevail over the other.
“An animal that has a shorter life but produces more children eventually leaves many of its copies to reproduce, as an animal that has a slower life and produces fewer children,” Bearhop said over the phone.
Some species may rock both paths.
Black hawks – gray olives with black or brown splashes on the head – can be resident or migratory.
– Climate change –
Those who live outside have a shorter life, reach maturity at a younger age and produce more chicks.
Migration can take place in the skies, underwater or through different landscapes.
Climate change can skew evolutionary tables against migratory species, “they have to deal with changes in multiple locations, rather than just one for residents,” said Bearhop, who teaches Animal Ecology.
They travel between breeding and non-breeding sites depending on the seasons, and depend on predictable weather patterns, such as winds and ocean currents.
But global warming is breaking these patterns through rising temperatures, changing rainfall, and changes in vegetation.
The Blue Whale roams between tropical births in the winter and high latitude feeding sites in the summer.
As sea temperatures rise, the abundance and distribution of food – plankton, fish and squid – change, with weaker females increasing and the gap between the births of offspring increasing.
– Size matters –
“Climate change is not happening in a uniform way and its effects are already showing that it is much worse at higher latitudes,” Bearhop said.
The Arctic, for the benefit of migratory birds, is one of these areas.
Scientists expect to see differences in reproduction and survival rates as a result of climate change.
Research also matters in size.
“Migratory birds tend to have a smaller body size than birds and bats, while migratory and swimming migrants tend to be larger than all mammals except bats,” the authors said.
Only larger walkers and swimmers can save enough energy to complete long-distance migrations.
The authors added that large birds have energy problems when they are forced to use flight fins.
“That’s why there’s no migration mouse, for example,” Bearhop said. “They can’t cover the ground effectively.”
by Eléonore HUGHES