A disappointing voyage

Mammals, birds and insects often migrate northwards to breed, timing their arrival with seasonal profusions of food. Large journeys are often made to evade parasites and predators, or to find climatic conditions that suit their breeding needs. Now, researchers from the University of Bath have found that for 25 migratory species – including caribou, shorebirds and monarch butterflies – climate change and other human pressures have reduced these benefits. Many species are still hardwired to continue the dangerous trips each year, even where the benefit no longer outweighs the cost. In many cases, this has led to lower reproductive success and higher rates of morbidity.