Six animals changing size before your eyes

ORIGINAL: New Scientist

06 February 2013

Michael Le Page

Many animals around the world, from birds to butterflies, are shrinking – although a few are growing larger. What on earth on is going on? 

Read more: "Withering heights: Why animals are shrinking"

The Canada lynx, also called the Alaskan lynx, feeds mainly on snowshoe hares. A study of 500 skulls suggests that its size has shrunk over the past 50 years. This could be due to fewer hares – a lack of food – or to warmer conditions that allow smaller individuals to survive and breed. (Image: Momatiuk Eastcott/Fuse/Getty

The semi-wild sheep that live on the Scottish island of Soay are also shrinking a little, and here the reason is definitely the climate getting warmer. Small individuals lose heat faster than larger counterparts, so are more vulnerable to the cold. As the world warms, more of the smallest individuals are surviving and thus the average body size of many species is decreasing. (Image: Colin Monteath/Hedgehog House/Getty)

A changing climate affects different animals in different ways. American martens are getting larger rather than smaller, for instance, perhaps because they can find more food when winters are less bitter. (Image: Sylvain Cordier/FLPA)

Just how complex the effects of a changing climate can be is shown by the dipper. This small bird uses its wings to swim underwater in fast-flowing streams, where it catches small invertebrates. In the Sierra Nevada in Spain, the weight of dippers has changed little over the past 20 years, but their wings have lengthened and their legs have shrunk. It's thought that because of a decline in river flow over this period, dippers are spending less time underwater and more time catching non-aquatic insects – favouring individuals with longer wings, which are better for flying than diving. (Image: Image Broker/Rex Features)

For cold-blooded animals, rising temperatures might seem a boon. But there can be serious drawbacks in the short term. As temperatures rise, these animals' metabolism speeds up and so they consume more energy even when inactive. If temperatures rise 6 °C by 2100, reptiles and amphibians will need to eat up to 75 per cent more food just to maintain their body size. For Komodo dragons, that would mean catching an extra 200 chickens a year. (Image: KeystoneUSA-ZUMA/Rex Features)

Fish like the Atlantic cod face a double whammy. Like other cold-blooded animals, they will need to consume more food and oxygen as temperatures rise – but oxygen is less soluble in warmer water, so there's less and less of it. That means fish will have to either stop growing sooner or migrate to cooler waters. The average weight of many species is expected to fall by as much as a quarter by 2050. Many fish are also shrinking for a quite different reason: unnatural selection caused by fishing. (Image: Gerard Lacz/Rex Features)

In warmer conditions, all kinds of cold-blooded animals – from bees and butterflies to bullfrogs and boas – develop more quickly and reach adulthood sooner. In the vast majority of cases, the rate at which creatures reach maturity speeds up more than the rate of growth, meaning animals end up smaller. Why this is so isn't clear, but it could have profound consequences for many species as the mercury soars. (Image: Roy Toft/NGS/Getty)