As a child I was awestruck by photographs and film of vast herds of wildebeest roaming across the Serengeti, and flocks of geese flying to the other side of the globe. Long-distance migration brought home to me that humans are not the only animals with purpose and intent. It also gave scale to the world we share.
Many of the larger migrations have disappeared or undergone steep declines as a result of human activity, report Princeton University ecologists David Wilcove and Martin Wikelski in “Going, Going, Gone: Is Animal Migration Disappearing?”. There is, say the scientists, much left to learn about the biological mechanisms underlying animal migrations, and conserving migration is critical to understanding it.
But how to save the great migrations, and why?
Taking the second question first, Wilcove and Wikelski present a number of examples that illustrate the ecological importance of migration. Take the case of salmon in the Pacific Northwest. By migrating upstream, spawning and dying, these very determined fish transfer nutrients from ocean to river, and this in turn provides food for smaller fish, including young salmon. Before European settlement of the region, between 160,000 and 225,000 tonnes of salmon migrated each year up the rivers of what are now the US states of Washington, Idaho, Oregon and California. Today, it is estimated that the biomass of migrating salmon is only 12,000–14,000 tonnes.
And then there are the creatures of the sky. Every spring, 30,000 tonnes of songbirds migrate from their wintering grounds in Latin America to breeding grounds in the US and Canada. Assuming these birds consume 10–35% of their body weight per day in insects, they are eating between 3,000 and 11,000 tonnes of insects per day. If the numbers of birds continue to fall, this could have a serious ecological effect on forests and farmland.
As for conserving great migrations, Wilcove and Wikelski note that most efforts to protect biodiversity have been reactive, responding to crises rather than anticipating them. But this will not work in saving migrations:
“[If] migration is seen as a phenomenon of abundance, then its protection will require decision makers to adopt a much more proactive approach to conservation – in effect, to protect species while they are still abundant.”
The social and political challenges involved in conserving animal migrations are enormous. Non-human animals are no respecters of international borders, and even where their travels are wholly within single countries, conservation requires the involvement of many different agencies and sectional interests.
However, say Wilcove and Wikelski, the payoffs would also be great:
“We can preserve phenomena that have awed and sustained us since the dawn of humanity. We can protect ecological processes that are integral to many of the planet’s ecosystems. And we can solve scientific puzzles that have baffled natural historians for millennia. If we are successful, it will be because governments and individuals have learned to act proactively and cooperatively to address environmental problems, and because we have created an international network of protected areas that is capable of sustaining much of the planet’s natural diversity.”
It’s a very interesting essay, and I recommend that you read it in full.