Tuesday, April 20, 2010


Hey—remember when this blog was about flycatchers? No? It wasn’t ever about flycatchers?! Well fine then. My apologies for letting this slip into more of a diary style blog than anything else. Things just haven’t been all that interesting while in graduate school. I’ll be on the move again soon. But I should probably at least talk about my research once or twice before I move on.

Willow flycatchers are kind of a drab little bird. But they certainly have personality. (And you thought this was a science based blog—ha!) The subspecies I work with is listed as endangered in California, and the southwestern subspecies is federally listed as endangered. Population declines since the 1940s were attributed to loss of habitat and an increase in nest predation rates. I should also mention that these guys nest in wet montane meadows and both the water in the meadow (largely from snow melt) and the riparian shrubs (mostly willow) are extremely important to them, at least in our study sites. When I say “our” I mean me and all the students that have been studying this little bird over the past decade. The project I’ve been working on has been monitoring the Sierra Nevada population from just south of Lake Tahoe, north to Lassen Volcanic National Forest since 1997. This summer will be the last year of the study.

One part of the breeding cycle that hadn’t been looked at in this population yet was the postfledging period. That is, the time between when the young leave the nest and when they migrate. So that’s what I attempted to study at over the past 2 years. To do this, I banded the young so I could tell them apart from each other after they fledged, and I located the little buggers daily to see where they were and how many of them were alive.

If you have never seen fledging birds just out of nest…you are missing out…so cute! They like to huddle together on a branch and make adorable noises. Science. Right. Sorry. Basically I found that between 46% and 76% of the fledglings will survive to the end of the dependence period (after which they don’t depend on their parents for food and protection). So to get better picture of why this is important, think about it this way:

Typically willow flycatcher females have 1-2 nest attempts per season. The chances of a nest surviving to fledge is usually about 50%. So if you have 20 total nests, 10 of them will reach the fledging date. If you had 3 nestlings per nest (which would actually be a little high) you would have 30 fledglings and fecundity (# fledglings/female) would be 3, if you had 10 females (probably low, I’m keeping the math simple). And some say an annual output of 2.23 young/female is the minimum needed to keep most populations of small passerines stable—so we’re good! But wait, say you lose another 50% of those fledglings after they leave the nest. Now you’ve got 15 fledglings/10 females, giving a fecundity estimate of 1.50 which is not going to stabilize the population.

More importantly, fecundity estimates from this study were already estimated to be below 2.23, before my research was done—meaning that we were already showing population declines while overestimating the number of young that make it to migration each year! Bottom line: these birds are simply not producing enough young to keep their populations stable. And a lot of loss occurs during the breeding season.

So…what do we learn after 10 years of studying a declining species? They are still declining! Sigh. What now? More on this later. I don’t want to bore you to death. What a cliff hanger!

1 comment:

skm said...

I enjoyed your brief overview, kinda felt like I was back in the classroom learning (sometimes I miss it). But, I want to know...what now? Is there anything being done to reduce loss of habitat and nest predation? Apparently these flycatchers have been studied for an ample amount of time, so now is any one taking action?