Poor Farallon Islands bird breeding season prompts alarm
Farallon Islands researchers are alarmed after recording one of the worst breeding seasons this year in the largest seabird breeding colony in the continental United States.
“I probably haven’t seen one quite this poor,” said Pete Warzybok, who manages the Farallon Islands program with Point Blue Conservation Science, where he has worked for 19 years. “I have experienced a couple of poor breeding seasons, but in that time usually one or two species did OK and others did poorly. This year it seems that across the board pretty much everyone did poorly.”
Point Blue, which has had researchers on the islands off the San Francisco coast continuously since 1968, recorded lower than normal numbers and poor breeding across all 13 species that nest there. Cassin’s auklets, which normally have about 75% breeding success had a rate of less than 10% this year. Only one pelagic cormorant nest was found — and later abandoned by the parents — when researchers typically see 150 nests.
For the chicks that were present, many starved as their parents could not find the right size of fish after searching several days for food. Some adult birds have also been found dead on beaches, Warzybok said.
“The adults are not just finding enough food to raise their young, but not finding enough food to feed themselves,” Warzybok said.
The cause of this drastic drop in breeding success on an island with nearly 350,000 birds is believed to be a weak El Niño weather pattern that occurred this year that affected California more acutely. The low winds reduced the upwelling of cooler, nutrient rich waters at the ocean depths to the surface. The strong upwelling near the Farallon Islands are what make the area so productive as a bird breeding haven, Warzybok said.
With less upwelling, the algae blooms that normally feed other prey species like krill and plankton were lacking, which in turn affects the food web. One result was the lack of juvenile anchovies and rockfish, which murres and rhinoceros auklets use to feed their chicks. Researchers tracked some adult birds using GPS monitors and noticed many were flying for multiple days in search of some food.
This is unusual, Warzybok said, as the waters around the islands are normally concentrated with young fish from which parent birds can draw from multiple times a day to feed their chicks. Researchers saw adults bringing back adult anchovies instead, which are too big to eat and resulted in chicks starving to death.
“As scientists, we try our best to be detached observers of ecological processes,” Warzybok said after the findings were released. “That said, as conservationists, we want to see a thriving ecosystem and it’s heartbreaking to watch seabird chicks starve due to a lack of suitable food.”
Meanwhile, out at sea, Jaime Jahncke who directs Point Blue’s California Current group, was also noticing anomalies. The three research cruises Jahncke and other researchers make during the breeding season from May to September are usually filled with bird and whale sightings. The birds were lacking and while there were many humpback whales, no blue whales were observed.
“Normally in July when we conduct our cruises and we run into common murres along our transects we tend to see always an adult and its chick swimming together,” Jahncke said. “This July we saw very few chicks with adult birds. Most adults were by themselves.”
As for the blue whales, Warzybok said they might have migrated to other areas in search of food. Warzybok said he recently read an article of rare blue whale numbers off the coasts of Oregon and Washington state.
Plankton trolls found that prey species were at deeper depths, another sign of the El Niño impacts.
While alarming, one bad nesting year isn’t necessarily bad news, Jahncke said. However, if multiple years like this occur it could have long-term negative affects on the seabird populations. Even if the population recovers next year, Warzybok is not resting easy as climate models are predicting these type of El Niño events to occur more frequently and intensively.
“If these events start to pile up and especially if what are considered moderate El Niños start to have the same effects as a severe El Niño, then we might have more severe consequences in the future,” Warzybok said.
After learning of the Farallon seabirds’ plight, Marin Audubon executive director Barbara Salzman called the situation tragic and worrisome.
“It’s alarming that that could go on for longer,” Salzman said. “It’s all the more important to get the ideal conditions and get the mice out of there. It’s all the more important that we focus on climate change.”
The mice Salzman refers to are the invasive house mice that were introduced to the largest of the Farallon Islands during the 19th century. The estimated 60,000 mice on the island have been causing harm to the ecosystem including eating some of the eggs of the nesting birds.
The U.S. Fish and Wildlife Service has a controversial proposal to drop 1.5 tons of rodenticide-laced pellets on the island to eradicate the mice, which is expected to result in the deaths of some birds. The California Coastal Commission is set to consider the proposal at a future date.
For Warzybok, the recent observations of poor breeding don’t change his views on the mice eradication plan.
“This is another way that we could use management to mitigate for the effects of climate change that we can’t control,” he said. “By removing the mice, removing that other pressure that is unnaturally impacting seabird populations, we can at least remove that pressure and give (the birds) a bit more of a chance to adapt and respond as climate change alters the marine ecosystem.”