Researchers have long known that smaller animals have higher metabolisms and tend to die younger than larger animals. Think about it – a mouse typically only lives about 2 years whereas an elephant in the wild may live 50-70 years, depending on the species.
After studying over 700 species of birds and 540 species of mammals, scientists discovered that migratory animals also live faster (mature and reproduce earlier) and die younger than non-migratory species. Their findings were recently published in Nature Communications. Interestingly, animals that migrate by walking or swimming (mammals, not including bats) are also bigger than their non-migratory relatives whereas animals that fly (bats and birds) are often smaller. Co-author Dr. Dave Hodgson was quoted in Earth.com saying, “We think that walking and swimming migrants are generally larger because only large animals can store enough energy, and use it efficiently enough, to make long-distance land or sea migrations viable. Among flying species, the opposite is true, as a large body mass makes flying more costly in terms of energy.”
Migration is indeed energetically quite expensive and risky. Think about the subspecies of bar-tailed godwit (Limosa lapponica baueri) that routinely make the longest known non-stop flight from Alaska to New Zealand (~9,000 miles one-way). That’s right, non-stop. Could you imagine taking a journey that long without stopping for a bite to eat? Here is satellite imagery tracking the movement of individual bar-tailed godwits (Limosa Iapponica) as they migrated from New Zealand to China, a distance of almost 6,000 miles:
Animals that migrate must adapt to multiple locations as compared to animals that stay in one location year round. This means that climate change may impact migratory species more than non-migratory ones. Migratory animals may develop faster and begin reproducing at earlier ages (and producing more offspring) to compensate for their shorter lifespans.
A similar study published earlier this year in Nature Communications examined the relationship between pace of life and longevity across birds. In that study, scientists concluded that environmental factors also contribute to longevity in birds. They found that birds living in areas with more predators developed more quickly and produced more offspring whereas those living in safer environments were able to take their time a bit more. They likewise reported that migratory birds die younger than non-migratory, which they speculate may be related to the speed in which the animals need to develop and return to winter habitats.
A Soriano-Redondo, JS Gutierrez, D Hodgson, S Bearhop. Migrant birds and mammals live faster than residents. Nature Communications, 11: 5719, 2020.
CR Cooney, C Sheard, AD Clark, SD Healy, A Liker, SE Street, CA Troisi, GH Thomas, T Szekely, N Hemmings, AE Wright. Ecology and allometry predict the evolution of avian developmental durations. Nature Communications. 11: 2383, 2020.