SAN FRANCISCO, March 25 (Xinhua) -- A research team has found that fully grown Galapagos penguins who have fledged or left the nest continue to beg their parents for food, and sometimes, parents oblige and feed their adult offspring.
It seems that humans are not alone in continuing to support offspring who have "left the nest."
"Through field seasons over the years when we were observing penguin behavior in the Galapagos Islands, we saw these isolated instances of adults feeding individuals who had obviously fledged and left the nest," said University of Washington biology professor Dee Boersma. "And now we've collected enough field observations to say that post-fledging parental care is a normal -- though probably rare -- part of Galapagos penguin behavior."
In a paper published online in The Wilson Journal of Ornithology, the team led by Boersma, who has studied Galapagos penguins for more than four decades, reported observing five instances of post-fledging parental care during detailed field observations of wild Galapagos penguins from February 2006 to July 2015. Newly fledged adults, called fledglings, are about 60 days old and sport a distinct appearance due to their lightly colored feet and cheeks, as well as a relatively new and spotless coat of adult plumage.
In many seabird species, parents continue to feed their offspring after fledging, at least for a limited period of time.
But this is not true for the world's 18 penguin species. Galapagos penguins are now only the second penguin species, after Gentoo penguins, to demonstrate post-fledging parental care. And Boersma does not expect to find more.
The researchers saw fledglings on the beach beg for food using distinctive vocalizations as adults emerged from the water after feeding. Some adults, presumably unrelated to the fledgling, would peck at the fledgling or move away. But the researchers also witnessed scenes in which a fledgling approached an adult, begged and received regurgitated food from the compliant adult. In most penguin species, including the Galapagos, parents and offspring recognize each other using a variety of cues such as vocalizations and location. Based on the juveniles' begging behavior, Boersma believes that adults who fed a fledgling were likely its parents.
Fledgling care is one of several behaviors that distinguish Galapagos penguins from other penguins.
Many of these peculiarities make sense when considering where they live, Boersma said. Volcanic in origin, the Galapagos Islands straddle the equator. Thus, Galapagos penguins must cope with extremes such as punishing heat on dry land and relatively cool ocean waters. The islands are made up of rough igneous rocks, and their oceanic food supply can swing between bounty and famine depending on climate patterns in the wider Pacific basin.
Both Galapagos and Gentoo penguin parents have been observed sticking close to their nesting site after the chick fledges so they can feed their fledged offspring. In other penguin species, many adults molt shortly after the young fledge and many migrate from their nesting area, which is why Boersma believes that few other penguin parents care for their fledglings after they leave the nest. Galapagos penguins may simply have evolved this behavior to increase their reproductive success and make the most of the bountiful times.
"In February 2017 when we were in the Galapagos, fully 40 percent of the penguins we counted were juveniles who fledged within the last few months," Boersma was quoted as saying in a news release from WU. "That would indicate that food is plentiful and this was a good time to breed. But in the Galapagos, especially with climate change, the good times can vanish in an instant."