Gannet foraging sharpens thinking about marine conservation

July 19, 2012 By Adele Rackley
Gannet foraging sharpens thinking about marine conservation
Colony of gannets.

New research into seabirds highlights the need for marine conservation to consider the different behaviours of males and females in the species it aims to protect.

For the first time, female have been shown to travel much further from the colony during the than males, and to rely on different .

This means the sexes could be affected differently by things like pollution and renewable energy installations, or changes in climate or policies.

A team led by Plymouth University studied a colony of northern gannet, Morus bassanus, at Grassholm, Wales, between 2006 and 2009. They used GPS trackers and chemical analysis of blood and to work out where, and what, the birds were eating.

'At a time when the development of is a key goal, our findings mean that effective protection of both sexes must occur at different scales,' says Dr. Stephen Votier of the University of Plymouth, one of the authors of the report which is published in .

Different between sexes is common in many animals but the reasons behind it are not clear cut. It's often thought that differences in body size make one sex more successful at competing for food, but gannet are very similar in size.

Gannet foraging sharpens thinking about marine conservation

To understand what could be behind the gannets' behavior, the researchers studied individuals of all ages – breeding adults and younger birds – throughout the whole annual cycle and across consecutive years.

GPS trackers revealed that, during the breeding season, females with young traveled much farther from the colony than the males when looking for food. But outside the breeding season, or among younger birds, there was no difference in foraging behavior.

This suggests that parental roles, rather than body size, could be important. Male gannets spend more time defending the nest, leaving females free to travel farther for food – although the trackers also revealed that their longer journeys did not keep the females away from home for much longer than the males.

Analysis of stable isotope ratios provided further detail on the gannets' diet. Isotopes are different types of the same chemical element, and their proportions vary in different marine creatures. When the gannets feed, the isotope ratios of their prey are reflected in the birds' blood cells and in new feather growth.

In particular, the isotopes revealed that male gannets eat a higher proportion of white fish than females. Because white fish species live much deeper than gannets can dive, it's likely that these are discards from fishing boats.

While it's not clear why males rely more on discards, it does suggest the sexes will be affected differently if fishery policies reduce discard levels, which would reducing a major food source for the males but potentially also reduce the risk for the hundreds of birds caught by fisheries every year.

Explore further: Gannet population under threat from global warming

More information: C Stauss, et al. Sex-specific foraging behaviour in northern gannets Morus bassanus: incidence and implications. Mar Ecol Prog Ser 457: 151-162, 2012. doi: 10.2254/meps09734

Related Stories

Biologist Shows Female Birds of a Feather Compete Together

December 15, 2009

(PhysOrg.com) -- With its flamboyantly decorated plumage, the peacock is a classic example of how males among many bird species are more visually eye-catching than their female partners. But new research, led by Columbia ...

The burly bird catches the girl

August 17, 2011

While the early bird might catch the worm, it's the quick bird that lands the ladies, according to new research into the running performance of an Arctic cousin of the grouse.

Brawn and speed make the grade during mate selection

September 12, 2011

Do more efficient and faster male birds win females over? New research from the United Kingdom suggests that the rock ptarmigan, the Arctic cousin of the grouse, does. University of Manchester researchers have found that ...

Scientists predict where seabirds forage

February 7, 2012

Researchers have used information about seabird colonies and food availability to create a mathematical model which predicts where they forage for food during the breeding season.

Recommended for you

Genomes uncover life's early history

August 24, 2015

A University of Manchester scientist is part of a team which has carried out one of the biggest ever analyses of genomes on life of all forms.

Rare nautilus sighted for the first time in three decades

August 25, 2015

In early August, biologist Peter Ward returned from the South Pacific with news that he encountered an old friend, one he hadn't seen in over three decades. The University of Washington professor had seen what he considers ...

Why a mutant rice called Big Grain1 yields such big grains

August 24, 2015

(Phys.org)—Rice is one of the most important staple crops grown by humans—very possibly the most important in history. With 4.3 billion inhabitants, Asia is home to 60 percent of the world's population, so it's unsurprising ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.