Thursday, April 10, 2008

The Importance of Individuals

Spring marks a switch in the focus of our research from marine mammals to seabirds. Within the last few weeks, the final bull (adult male) elephant seals left the island, but haulout areas are still filled with cows (adult females), immatures (sexually immature individuals) and weaners (pups from this year which have just been weaned). Elephant seals from as far away as Año Nuevo and San Miguel islands swam their way to Southeast Farallon and are currently basking on its shores.
An intern records the green
tag on this Elephant Seal,
allowing us to identify the
seal and where it came from

While we continue to re-sight tagged elephant seals, we are also working with a variety of seabird species. For the Common Murre, which number over 250,000 in the Farallones, we are re-sighting individuals (marked with a unique combination of colored/metal numbered bands on their legs) from blinds and identifying their territories before they begin nesting. We will continue our observations throughout the breeding season in order to collect data on egg laying, hatching and chick fledging success at three different locations through out the island.

Common Murres with
their individual color bands.

For Cassin’s Auklet, observations are more complex. This species breeds in burrows, as opposed to nests above ground. In order to collect data on the breeding success of these birds, we have specially constructed nest boxes which can be opened at the top, allowing the researcher to see the bird with minimal disturbance to itself or its ‘burrow’. Due to efforts in previous years,
the age of some of these auklets (identified by a numbered metal band) are known. Age specific data is rare and difficult to come by in many sea-going bird species which makes the information collected on these individuals unique and valuable.

Here, an intern checks nest
boxes for breeding auklets.

The information we are able to gather from individually marked animals allows us to track them over many years and determine mate fidelity, site fidelity, and lifetime reproductive success. With both of these species, as with most of the wildlife on Southeast Farallon Island, PRBO has decades of data and information on population sizes and breeding success. This means that the data collected this year can be compared to that of previous years. When this information is combined with our knowledge of past and current climactic and oceanic conditions, we can gain a better understanding of how environmental factors may influence the breeding success and population trends of marine birds.