Nature Blog Network

Saturday, June 30, 2007

Seabird Diet Switched From Fish to Invertebrates, Possibly Linked to Overfishing

Seabird Diet History Revealed Through Analyisis Of Museum Samples

Using feathers from museum collections all over the world, a University of Guelph integrative biology professor has tested a new hypothesis about what led to population decline of a species of seabirds in Canada.

Prof. Ryan Norris conducted a historical analysis of museum specimens of marbled murrelets going back more than a century to examine how dietary changes may have affected the seabirds’ numbers.

The study, which will be published in the August issue of Journal of Applied Ecology, also illustrates how scientists can use museum specimens to figure out what led to a species decline and to help focus conservation efforts.

“One of the biggest unknowns for endangered or threatened species is how their populations fluctuated naturally before human disturbances,” Norris said.

“But there are millions of specimens in museums across the country, many of which were collected before habitats started to decline and that can give you really important baseline information for designing plans to conserve species.”

Norris decided to examine how marine diet over the last 100 years might have influenced the birds’ populations by analyzing the stable carbon and stable nitrogen isotopes, chemical signatures that become fixed into the marbled murrelets feathers when they’re grown.

Their isotope analysis showed that prior to 1900, the birds were feeding most on fish, but that by the 1970s, 80s and 90s, their diet consisted of marine invertebrates, which are much less energetically rich than fish.

“Murrelets have to catch around 80 to 100 marine invertebrates to get the same nutritional value as in one forage fish,” Norris said.

The researchers concluded that the seabirds’ population changes in Canada after 1950 were likely influenced by a decline in the amount of fish in their diet. It’s an important finding because it suggests that to save the species, conservation efforts should be refocused.

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