Thursday, July 26, 2012

Wild Nights at Club Farallon


The last month or so on the Farallones has been our busiest time of year. For us that means 16 to 20 hour days and lots of night work. Many of the species that breed on the island spend their days foraging at sea and only return to the colony at night. This both maximizes the amount of time they can spend looking for food and reduces the risk of predation from Western Gulls when they return to the colony. This means that if we want to learn about these birds, we must be active when they are and that means mist netting birds after dark.
Long exposure shot of mist-netting. The red lines are the trails from our headlamps as we move around the net.
Mist netting entails setting up a 12m long fine mesh net on Lighthouse Hill at night and waiting for birds to fly into it.  When a bird gets caught in the net, it is quickly extracted, measured and banded. We usually also collect some additional  measurements such as the depth of their bill, length of the wing, weight and whether or not they have a “brood patch” (an area of bare, highly vascularized skin that transfers heat from the adult to the egg and keeps it warm while it develops). This information can help us to determine the physical condition of the bird, its sex and whether it is a breeder or not. 

Ashy Storm-petrel
When the target bird is the ashy storm petrel, the net is opened from 1030pm-130am and a recording of a flight call is played to attract them to the net. It is a long night and can be quite tiring, but it is always exciting to get the chance to see these elusive birds and learn more about how they are doing. The goal of the mist netting is to get an estimate of the population, by examining the number of birds that are banded that evening or have already been banded previously. While Ashy storm-petrels are the most numerous on the island we often also catch Leach's storm-petrels and sometimes we even catch something really special like a Fork-tailed or Tristram’s storm-petrel. These rare visitors are never seen but just happened to bump into our mist net one night.
Leach's (foreground) and Ashy Storm-petrels caught side by side in the net
Rhinoceros auklet netting is a little less intense and happens from dusk until about 1030pm. The goal of this netting activity is similar to the goal for Ashy’s, to examine population trends by marking and later recapturing banded individuals. Auklet netting also allows us to study their diet by collecting diet samples from the captured birds. In order to feed their chicks, Rhinoceros Auklets collect several fish just before returning to the colony. They hold these fish in their bills (sometimes as many as 10 fish at once!) and dutifully carry them back to their waiting chicks.

Rhinoceros Auklets with fish (image copyright Verena Gill)
Of course, when they get caught in our mist net, they drop what they are carrying and we are able to collect these diet samples in order to determine what prey they are finding and to learn about which species are most abundant in a given season. We bring the dropped fish into the lab and identify them to species and also take some measurements on the prey. 
Measuring a juvenile rockfish
This year, juvenile rockfishes, salmon, barracudina, sablefish, Pacific saury, greenlings, flatfish, and even octopus were commonly found in the rhino diet. 

So, if you have ever wondered what a “night out” is like for Farallon biologists, now you know. Mist nets, fish and getting to work with some of the most amazing and elusive of the island wildlife. These are our “wild nights” on the Farallones. Check out the video below to see what it looks like.

video