Cormorant colony in 2007
Same colony this year
In early April, we began receiving reports of unusually high numbers of dead cormorants washing up on local beaches. The indications were that most birds appeared emaciated but not suffering from disease. It seemed birds were struggling just to feed themselves and lacked sufficient food to attempt breeding. Mystery solved? Not exactly. It simply raised another question, why would a lack of food, primarily juvenile rockfish and Northern anchovy, affect only Brandt’s? Many other seabirds on the Farallones eat the same fish, yet they seemed unaffected. Until recently that is…
Although the warm weather and sensational visibility were enjoyed by the island biologists, it seemed to have unfortunate consequences for the breeding birds. Coincident with the decreasing wind and increasing temperatures, Common Murres began abandoning eggs and chicks in unusually high numbers. Murres almost never leave an egg alone due to the high risk of predation by gulls. This year, we have observed numerous birds simply get up and walk away, leaving their egg or chick unattended and vulnerable. A further indication of poor foraging conditions is the increase in adult murre aggression toward unattended chicks. With no parent to protect them, vulnerable chicks are being harassed unmercifully.
To add to the confusion, during this period when murres were taking a turn for the worse, Brandt’s cormorants finally appeared. Not in the volume we would expect at this time of year, but a small number of birds have showed up, set up nests and are now incubating eggs. And so the mystery continues. The unusual patterns emerging this year demonstrate once again the invaluable perspective that PRBO provides on the Farallones. This year is just the latest indication of new changes occurring in marine ecosystems. The mysteries developing from these changes can only hope to be solved by examining long-term data sets such as those from the Farallon Islands.