Last week I was lucky enough to spend a very pleasant morning out on Humble Island with Heidi Geisz, one of the birders, and Gary Jirschele. Gary and I had come along to help Heidi with her work on Southern Giant Petrels. Heidi works for Bill Fraser and Donna Patterson who have been conducting research for many years on several species of birds around Palmer Station - Bill left on the last ship after celebrating his 30th year at Palmer!
Their Giant Petrel work has been going for about 10 years and began when Donna spent many days over several years sitting with the adult Giant Petrels to acclimate them to the presence of humans. They are now able to visit 24 nest sites throughout the summer and weigh and measure the chicks every two days. This work, in addition to work with satellite transmitters on breeding males and females and various censuses throughout the season, allows the birders to acquire basic data on the demography, breeding biology and foraging ecology of Giant Petrels.
They have found that the adults can travel up to 3000 miles over several days to forage for food on the ice pack edges (they scavenge for carrion and also eat live food like krill and squid), but that they also forage very close to home. The females tend to travel further than the males, as they are out competed by the males. Another intriguing result is that the populations of Giant Petrels on islands around Palmer Station have been increasing over the past couple of decades, whereas other breeding colonies in Antarctica and the sub-antarctic islands have been in decline. The chicks are looking like gangly adolescents at the moment - they were born in early January and will remain in the nests until mid-May when they will fledge. During the periods between hatching and fledging the chicks are fed by both parents, who may be gone for days foraging for food.
In the meantime the chicks protect themselves from predators by vomiting up the contents of their stomachs (a nasty smelling oily substance). This means that when we go walking around on the islands we have to be very careful not to go too close to any nests as the chicks may vomit up the contents of their stomach - which can represent the last weeks food supply - and this leaves the chicks very vulnerable to starvation.
This is harder that it sounds - the nests are very well camouflaged. When we were walking around on Humble Island I was following Heidi to the next nest and a couple of times I wondered why we had stopped - not realizing that there was a nest right next to our feet! We spent the morning going around on a circuit of 24 nests and weighed the chicks and measured their beak length. A few of the nests had parents around, but they didn’t seem to worried about us being there - which is a good thing as they are pretty big birds with up to a 6 foot wind span.