[Tweeters] What I learned about the Cassin's Auklet wreck

Rachel Lawson rwlawson at q.com
Tue Dec 30 20:38:17 PST 2014


Thank you to everyone who emailed me about my Cassin's Auklet post. Barry
McKenzie was particularly helpful, and pointed me towards recent discussions
on OBOL. Mike Patterson and Range Bayer's OBOL posts were very informative.
Here is a summary of what I found:



Preliminary data show that the large numbers of juvenile Cassin's Auklets
that have been washing up dead on beaches from here to California died from
starvation. There is no evidence of disease or exposure to toxins.



As in all species of birds, there is high mortality in the first year of
auklet life. Even when adult auklets are able to find plenty of food for
their chicks, food availability in the winter range may not be enough to
support all of the young birds after they leave the nest. Winter storms
make it even harder for these inexperienced juveniles. It is quite normal
for thousands of young auklets to die in their first winter. This summer,
Cassin's Auklets, particularly in colonies on Vancouver Island, had higher
than usual nesting success. Even if the percentage of juvenile birds that
died of starvation was no higher than usual, there would be larger absolute
numbers of juveniles dying.



Why is there not enough food for these auklets? One reason may be that
warmer ocean temperatures (climate change? normal cyclical weather patterns?
both?) result in less upwelling, and less upwelling means that the
zooplankton (krill) that make up the entire Cassin's Auklet diet did not
rise from the colder ocean depths and were not available to the auklets. A
research ship from the California Current Ecosystem Studies program did
indeed find a shortage of zooplankton in September.



Why are so many of these dead Cassin's Auklets showing up on our beaches?
Warm near-shore waters bring some deep-water seabirds closer to land, and
when they die, westerly winds push them onto the beaches where birders find
them.



If I have made any errors of fact or interpretation, or if you have any
additional information or ideas, please let me know.



Rachel Lawson

Seattle

rwlawson at q.com







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