Blue-footed Boobies Take a Puzzling Dive
An unexplained sardine shortage may be putting the Galápagos’ blue-footed boobies in a tailspin.
Known for their bright blue feet and lively mating dance, blue-footed booby populations are plummeting in the Galápagos.
The population, previously containing about 20,000 birds, has fallen more than 50 percent in less than 20 years, according to a new study published in Avian Conservation and Ecology.
Dave Anderson, professor of biology at Wake Forest University and lead author of the study, says the decrease is likely due to an unexplained disappearance of sardines from the birds’ diet. As a consequence, adult boobies are no longer breeding. When they die, they won’t be replaced by any young.
In 1997, scientists started noticing an alarming trend at blue-footed booby breeding colonies in the Galápagos—they were empty. At first, seabird ecologists thought the lack of breeding was an isolated occurrence. But after three years of little to no breeding activity, Anderson says he and his colleagues began to worry.
“That was the start of the conversation,” he says. “We started to ask ourselves, ‘Is something weird going on with the blue-foots?’” In 2011, Anderson and Colorado state seabird biologist Kate Huyvaert received funding to begin a comprehensive survey of blue-footed boobies in the Galápagos. From May 2011 to June 2013, a field team monitored breeding at three to five month intervals at four of the largest breeding colonies. The results of their study show little to no breeding activity and only 134 fledgling birds during the period.
“It was alarming,” Anderson said. "This was a drastic change from the 1980s and 1990s, when young Blue-foots were common throughout the archipelago."
Studies previously conducted at booby colonies on Española show successful breeding occurs only when the birds had an almost 100 percent sardine diet. Recent Galápagos study identified sardines as less than half of the Boobies' diet.
It’s not just that the birds’ breeding attempts have been unsuccessful—not many birds are trying. Anderson estimates the number is only about 10 to 15 percent are making an attempt. “In each reproduction attempt it’s as if they’re forecasting conditions just aren’t going to be good enough to even bother.”
So now the question is: Where are the sardines? says Johannah Barry, president of the Galápagos Conservancy. “Are they being overfished, are they leaving Galapagos waters due to climate change or other pressures?” she says. “If they are leaving what other fauna might be impacted?”
“We have a convenient explanation that isn't anthropogenic,” Anderson says. “But if humans are in fact contributing to this decline we need to get to the bottom of it now rather than five years down the road when you have the equivalent of 75-year old humans trying to breed.”