Tuesday, September 12, 2017

Post #116 - Info sought on grebe nesting failure!

This is a different sort of post as I am really looking for reader input on a bird health/conservation issue that I have recently found curious and disturbing. I am going to speak very generally about large a nesting population of Clark's and Western Grebes somewhere in Northern California. I am doing it this way since I don't want to outright publicize the location, but I am certain that many of you will know the spot to which I am referring. If you do, please just keep it under your hat, thanks. So, with that caveat out of the way, I want to field opinions as to what seems to be a complete nesting failure of a population of several hundred if not several thousand grebes. 

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......

3 comments:

  1. 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.

    A 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

    ReplyDelete
    Replies
    1. 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.

      Delete
  2. There 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.

    ReplyDelete