Wednesday, September 20, 2017

Post #117 - Quick follow-up to last week's Grebe post

Before we dive into the grebe stuff, I'd like to take a second to ask you to take a look at "A Symphony of Feathers" a writing, birding, conservation, and community project from a friend of mine, Devin Griffiths. Devin and I first met when I lived in Massachusetts. He was a strong supporter of my 2014 "Biking for Birds" project and even interviewed me about it for this, his current project. He's a great writer and great guy, so please take a second to check it out! OK, grebe time.....

For those that didn't read last week's post, I described what seemed to me a colony-wide nesting failure of a large population of Clark's and Western Grebe on a freshwater lake/marsh here in California. Hundreds of birds collectively laid thousands of eggs, but only a few chicks seemed to have hatched. I used this blog to source some hypotheses as to what might have caused such a large scale nesting failure, and I received a few interesting responses.

Western Grebe - Aechmophorus occidentalis
Canon 100-400mm f/4.5-5.6 IS II on EOS 7D2 Mark II
1/3200 at f/7.1, ISO 400

The first suggestion, as provided by both a blog reader and someone with weekly if not daily access to the colony in question, was that otters were in large part to blame. I didn't know this, but apparently otters are voracious predators, eating all sorts of stuff beyond what I assumed do be a fish-only diet. This idea seems plausible but I do not think is the entire story. I say that for two reasons. First, I spent several days kayaking through the colony and did not see a single otter. There would have to be dozens of them to devour all the hypothetical chicks. Second, many of the eggs hadn't hatched, even well-beyond the 24-day incubation period of Clark's and Western Grebes. Predation of any sort would explain a disappearance of chicks but not the apparent corruption of otherwise intact eggs upstream of that point. So, otters are a best a partial explanation.

Western Grebe - Aechmophorus occidentalis
Canon 400mm f/4 IS DO II + 1.4x III on EOS 1D Mark IV
1/3200 at f/5.6, ISO 400

Other ideas that postulated were water levels or pollution/toxicity though nothing terribly specific beyond that was suggested. Either of these could have widespread effects and affect the nesting success of the entire population. That seems consistent with the colony-wide problems that I observed. Intrusion by boaters was also suggested though my inflatable kayak was the only boat that I saw near the colony on my 3 independent visits. So, unless I was single-handedly responsible for the death of thousands of eggs and chicks, I don't think boating disturbance was the primary (or even a significant) cause. But others might know better on that front.

So, it seems as it the mystery will continue. Interestingly, a colony of Grebes in Clearlake, California experienced similar problems in 2014; From 3,500 nests, only ~20 chicks fledged that year. So, whatever is happening, it seems to be a big deal. We as a community need to keep our eyes on disturbing trends such as these.

More pelagic trips coming up for me, so maybe I'll run into you aboard either Alvaro's Adventures or Monterey Seabirds!

No comments:

Post a Comment