It takes decades for some migratory animals to learn their routes, and this knowledge can be lost in a generation if their journeys are interrupted.
Every spring, herbivores such as bighorn sheep and elk migrate to higher latitudes or altitudes, following the appearance of tender and particularly nutritious new vegetation as it emerges from the melting snow. The behaviour is known as “surfing the green wave”. But is knowledge of these routes inherited genetically, or must it be learned?
To answer this question, ecologist Brett Jesmer and his team at the University of Wyoming studied how migratory animals behaved when moved to new locations. They studied data from 129 bighorn sheep fitted with GPS collars in their native environment – where they had resided for over 200 years – and compared their movements to those of 80 sheep translocated to new environments.
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In their historic habitats, 65 to 100 per cent of bighorn sheep typically climbed 1000 metres up mountainsides to graze on new vegetation as it appeared in spring. By contrast, only 7 of the translocated sheep behaved the same way – all of which had been introduced to local populations which were familiar with the landscape.
“It’s unlikely that a translocated individual will ever migrate in its lifetime,” says Jesmer, “but it will accumulate knowledge, and pass that onto its young.” Over generations, this cultural knowledge of good foraging locations builds into a migratory route, suggesting those animal populations that have lived in an area longest will migrate furthest.
Moose moving
The researchers expanded the study to 189 GPS tagged moose and confirmed this idea. The largest migratory ranges were seen in populations that had been established the longest. Predation and disease had no effect on the size of the migratory range, suggesting the migratory knowledge was shared among the herd rather than being dependent upon select individuals.
Finding good forage locations is essential for these herbivores, which must put on enough fat during the summer to see them through the long winters. Because migratory animals track the emergence of nutritious green shoots they can maximise their energy intake and typically outnumber non-migratory animals. As such, the new findings have implications for the conservation of threatened wildlife.
“If we don’t protect the routes from summer to winter range and migrations are cut off, within a few generations, centuries of knowledge are lost,” says Jesmer. “We won’t expect them to start migrating again for decades, possibly up to a century.”
Science
