Fatty-fish food makes for brainier seabirds

Young seabirds which do not eat enough fat are slow learners and are less likely to grow into successful adult birds, according to a new study.

The finding could explain some of the dramatic declines seen in seabird colonies during the past 30 years, where climate change or human interference has reduced the number of fatty fish for the birds to feed on.

Alexander Kitaysky, from the University of Alaska Fairbanks, and his colleagues monitored the development of 20 red-legged kittiwakes, born in captivity. The chicks were divided into four groups, with each group being fed a different diet. Five lucky chicks were able to gorge themselves on silverside, a fatty fish. Another five were allowed to guzzle rainbow smelt, a low-fat fish. The remaining chicks were given restricted diets of either silverside or rainbow smelt.

In the wild, kittiwakes have to learn to look for particular colours and patterns in the ocean to find the best places to fish. The scientists tried to recreate this for the captive chicks by making them search for their food among a chequerboard of different coloured bowls. Chicks on the unrestricted fatty diet quickly learned which bowls contained the food, but chicks on lean rations were very slow learners and never really worked out the colours and patterns associated with their food.

"The ability of kittiwakes to associate the colour of a dish with the presence of food decreased proportionally with the magnitude of nutritional stress they had experienced during development," write the scientists today in the Proceedings of the Royal Society B: Biological Sciences.

The scientists believe that their study helps to explain the precipitous decline in seabirds seen on the Pribilof islands, in the south-east Bering Sea, over the last three decades.

A climate shift in the north Pacific and Bering Sea in the mid-1970s resulted in fewer lipid-rich (fatty) fish around the islands. By the early 1980s red-legged kittiwake populations on the islands had plummeted by 50%. "The results of our study suggest that declines in availability of lipid-rich fish - caused by climate change or human-induced - are likely to result in an inferior quality of seabirds in later life and an increased chance of mortality," write the scientists.

Previous studies have shown that passerines (perching birds) such as blackbirds and sparrows are incapable of learning their mating songs if they do not have a good diet as a chick. Meanwhile, mammals such as rats have been shown to have slow brain development if they are not fed properly at birth.

A healthy diet is clearly vital for normal development in many creatures. What is not clear is how much climate change and human interference is likely to impact on seabird populations. Many coastlines could be heading for a new generation of retarded seabirds and population collapse.