Grebes EVERYWHERE, but no chicks to be found anywhere?!?!?
I first visited this particular location on July 5th of this year, and I was completely blown away by the number of birds I observed. I saw only 1 chick on that visit, but countless other birds were sitting on eggs at that time. I figured I had arrived just on the front end of what was surely going to be an huge hatch-out of grebe chicks in coming weeks. Consulting the Cornell Lab page on Western Grebe, it stated that the incubation period for the species is 24 days. I figured that if I returned in a few weeks, more of the eggs would have hatched by then. You can understand my surprise when I returned on July 24th - 19 days later - and found zero recently hatched chicks. If all of the eggs that I observed on the July 5th were just-then laid, sure, it would make sense that none of them had reached the required 24 days of incubation to hatch. But that seems really unlikely, particular once you read on.
Western Grebe on nest - Aechmophorus occidentalis
Canon 400mm f/4 IS DO II + 1.4x III on EOS 1D Mark IV
1/2000 at f/5.6, ISO 400, handheld
Fast forward to my third visit, on August 13. I thought for sure there would be all sorts of chicks by then, but, again, I found loads of birds sitting on eggs and no chicks (well, one, photo below). At that point I realized that something had to be very seriously wrong as the entire population hatched effectively zero young from what were certainly thousands of individual eggs from hundreds of individual pairs. To complete the timeline, a friend of mine visited the area this past weekend, on September 9, and said that all the nests had been totally abandoned. What the heck is going on?!?!!??
Western Grebe with chick - Aechmophorus occidentalis
Canon 400mm f/4 IS DO II + 1.4x III on EOS 1D Mark IV
1/1600 at f/8, ISO 400, handheld
What was really strange is that the adults looked generally healthy to my eye. Notably, I did not see a single adult bird catch or consume a fish in any of my three visits. That lead me to wonder if a food shortage could have affected the nesting success of the entire population (though that would more likely affect chicks than unhatched eggs)? I also wondered if the unusually heavy rains that Northern California experienced this winter might have contributed. Perhaps increased runoff deposited more of a certain toxin in the water? Altered the sediment composition? Changed the osmolarity, etc? I really have no idea what cold explain the apparent nesting failure, so I'm really grasping for any possible explanation.
So, I am looking to generate some discussion about this topic. I'd love to have what comments people make as official blog comments below. That way they are part of the post and others can read follow whatever discussion we can together generate. So with that, I want to hear what people think is going on with these birds......
Some possibilities would include toxins/teratogens leading to developmental failure. Problems with oxygen supply if the nests had become flooded. Problems of the eggs not being properly incubated at some point, either due to flooding or to disturbance.
ReplyDeleteA quick google revealed the following that might provide some ideas (they are talking about artificial nesting platforms for western and clark's grebes - the intro and/or discussion might have the seeds of some ideas):
https://www.wildlifeprofessional.org/western/transactions/transactions_2009_2.pdf
Dom
Also, can you rule out hatching followed by loss of chicks? If there is a disease or if there is a very effective new predator that found its way to the lake.
DeleteThanks for the info. It seems as if there are a number of possible explanations, none that we can pinpoint for certain - ugh.
DeleteThere was a major colony failure a few years ago at Clear Lake due to predation, by otter as I recall. My info came from Faith Rigolosi, who runs Eyes of the Wild tours there. Possibly your colony suffered the same fate.
ReplyDeleteI heard the same thing. I wonder how much of that situation is common with what/where I observed.
DeleteI don't know the site, but there have been some severe cases of metal pollution in California.
ReplyDeleteIf memory serves, selenium poisoning impacted the Salton Sea birds quite badly and it would be logical that chicks building up their bodies with contaminated food might succumb while the adults still survive. Sampling the local fish should give an indication.
Pollution always seems like a likely culprit, but from what others have said it doesn't look as though there is one perpetrator. Looks like it would be good to do some actual research on the colony. Might make a good PhD thesis for some ecology-type grad student.
DeleteDid you do a lake-wide survey? Once hatched, the young and their parents do not stick around the colony area for long and you will have more success seeing them elsewhere on the lake and can draw a much stronger conclusion if a full lake survey is conducted.
ReplyDeleteNo, mine was admittedly a small sample size. But from what I have been hearing, my observations are consistent with those of others and the colony is known to have major problems at present.
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