Seabird Diet History Revealed Through Analyisis Of Museum Samples

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.”

For example, there is little historical information about marbled murrelets because the birds are highly secretive and difficult to study, he said. “The first murrelet nest wasn’t discovered until 1975 so gathering information about the causes of their decline has been extremely difficult.”

But Norris was able to reconstruct the diet of the seabirds by utilizing museum specimens dating back to 1889.

Working with Peter Arcese of the University of British Columbia’s department of forest sciences, he visited dozens of museums across North America collecting feathers from marbled murrelets gathered from the Georgia Strait — the waters between Vancouver Island and British Columbia’s mainland.

The seabirds spend more than 90 per cent of their time on the sea, but they travel up to 100 km inland to nest in old growth forests. The species numbers have been dwindling in Canada over the past 100 years, a drop that scientists previously attributed to a loss of coastal old growth forests.

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.

“Instead of spending all their time and money on the murrelet’s nesting habitat, conservationists and managers may have to take a step back and evaluate how to optimally allocate resources to conserve this species,” said Norris.

“If we keep pouring all of our money into the current plan, it’s possible this amazing seabird will continue to decline anyway.”