The seabird breeding season is wrapping up at Año Nuevo Island–gull chicks are flying to the mainland, auklet chicks are silently leaving their burrows at night and heading out to sea, and researchers are settling in at the computer for a long season of data crunching ahead. The obvious question to ask this time of year is “how did the seabirds at Año Nuevo do in 2012?” The numbers have not all been crunched yet, but it seems to have been an about average year for most breeding seabirds at Año Nuevo Island. Rhinoceros Auklets, Cassin’s Auklets, Brandt’s Cormorants, Pelagic Cormorants, and Western Gulls all managed to produce a fair crop of healthy chicks.
Rhinoceros Auklets laid 23 eggs in the ceramic nest modules installed by Oikonos in 2010. 19 chicks hatched in the modules, for a hatching success rate of 82%. Chicks are currently fledging and the we don’t have the final numbers on survival yet. Rhinos also were successful in natural burrows this year, and damage to burrows from erosion was greatly reduced after Oikonos restored native plants in 2010. In 2011 only 3% of burrows were damaged by erosion, compared to 11% damaged in 2010, and a high of 67% damaged in 2000. 2012 numbers have not been analyzed yet, but erosion rates were low, similar to 2011. The breeding population of Rhinos has been around 200-250 adults since 2003. With improved habitat we expect that number to grow in the future if ocean conditions are favorable.
Northern Anchovy and juvenile Rockfish are the preferred prey of Rhinoceros Auklets at Año Nuevo, and both fish species were scarce this year. Rhinoceros Auklet chick diet was primarily composed of Pacific Saury, an offshore schooling fish, and Market Squid in 2012. Rhinos were bringing back an impressive number of Pacific Saury for their chicks, and this year we recorded a bird carrying 20 fish in its bill–a record for Año Nuevo Island!
There was also some bad news for Rhinos this summer– we found oil on five live adult Rhinos in June/July.These are the first oiled Rhinos we have seen at Año Nuevo since 2005. All the birds were lightly oiled and seemed healthy, and we were able to quickly remove the oiled feathers and release them. Repeated leaks of oil from a sunken ship off of Half Moon Bay killed many Rhinos during the 1990’s and 2000’s, and the habitat restoration efforts at Año Nuevo Island were funded as part of an effort to restore populations of seabirds killed by this pollution. California Department of Fish and Game is testing samples of the oil found this year to determine the source. This oil may have been from a natural seep and did not turn into an oil “event,” but it is a good reminder that oil pollution is still an existential threat to the Rhinos at ANI—with only 250 breeders, a major spill could be devastating.
Cassin’s Auklets are a relative of Rhinos, but much smaller—Rhinos are the size of a small chicken, and Cassin’s are the size of a robin. Cassin’s were first found breeding at Año Nuevo Island in 1995, and in 2012 we’ve had a record high 62 confirmed breeders. As a burrow-nesting species, Cassin’s have also been enjoying the benefits of the habitat restoration, and population growth has been centered in the newly vegetated central terrace. 2012 was a productive year for Cassin’s Auklets, and several pairs laid a new egg after their first chick had grown up and fledged. This strategy, termed “double-clutching,” is unusual among seabirds and allows Cassin’s Auklets to produce more young when environmental conditions are good for breeding. Our last Cassin’s Auklet chick hatched August 14th and isn’t expected to fledge until September!
Western Gull nest numbers at the island have been in slight decline since 2005–there were just under 900 nests this year, down from over 1,200 in 2005. Each breeding pair of gulls fledged an average of around 1 chick this year, which is on par with our long term average of 1.13 chick per pair from 1999-2011. It gives a little window into how hard life is for a gull chick to realize that each pair usually lays 3 eggs, and usually only 1 chick survives.
We are still working on our cormorant data, and I’ll provide an update on nest numbers and productivity when I know more!
The plants from the restoration are doing well, and this fall we will be spreading more native seed and planting in the few bare spots left. We put out the plants to enhance Rhinoceros Auklet habitat, but the Western Gull chicks, like the one in the photo below, seem to like the new plants too!