Scissor-tailed flycatchers (Tyrannus forficatus) are highly uncommon in Missouri, but there is a pair nesting right by Mount Doom and yesterday we saw them flying in the distance, against the rocky nuclear waste site. The bird guides do not put these lovely Texas Hill Country birds in Missouri, except for with a rare bird dot, but here they were. First one, then the other flew low, then up onto a telephone pole. The birders with this Audubon-sponsored outing told me that they had a nest earlier in a precarious stem, now destroyed. Others online said there was still a nest with eggs which we did not see. I guess this is the advantage of an active community of birders.
I was glad to see these Texas favorites, but prefer to think of them back in Texas, soaring over the natural granite and gneiss around Llano, or over the limestone outcrops around San Antonio. These great flycatchers remind me that every bird is an individual. Every migration path is particular, taken by many, but flown separately. The terrain is a mosaic, with cerulean warblers here, not there, though the habitat looks identical. Pine warblers were in these pines at Busch Interpretive Center last year, but not this year. The collective knowledge of hundreds of St. Louis birders tells us where and when, then shares it on MoBirds for all. Or you can wait for a St. Louis Audubon Society field trip and learn for yourself.
Are you wondering about Mount Doom? So was I. Is it the reason for this large and lovely natural area around Weldon Springs, so close to St. Louis? After all, how bad could it be when there is a high school right in its shadow. Turns out, it is about as bad as it gets, horrible waste, horrible actions on all sides, towns destroyed, and then it was buried. Is this a good solution? Would it be the solution today? What should be done if you have a munitions factory, nuclear waste, and all kinds of problems like that? They got the contaminants out of a quarry, came up with a plan, then executed it. The result is what the birders call Mount Doom and the government calls The Weldon Spring Site. Is it good or bad? Well, life is much too complicated for those terms. I don’t know enough about the whole thing except to know it is finished. We should keep gathering careful data on the people around there and think hard about what waste we generate, for once we have it, there are are no easy answers. I’m reminded on a much smaller scale of the paint factory on the shores of Lake Waban, on the Wellesley College Campus. There the remediation was a complex mix of removal, burial, and isolation.
But what about those flycatchers? Why do they have such long tails? Do they suffer from edge-of-range effect here? I found one interesting study by Laura González-Guzmán and David Mehlman, published in Ecology Letters in 2001 (volume 4, pages 444-452). They talk about several interesting points. One is that there are sink and source habitats. A sink habitat is one where young disperse to but then fail to breed, so the place sucks in naive organisms without ever exporting any. Such places are likely to be more common on the edges of ranges where conditions might be marginal. Our Mount Doom location would be a sink if the birds that come there could never successfully breed. I hope that is not the case, but do not know.
Even if they could breed, an edge-of-range habitat might be unsuitable in more subtle ways. One way biologists have of getting at this is to look at how symmetrical the birds are. The argument goes that bilateral organisms like us will be symmetrical if we have developed under good conditions. Symmetry has been argued as a trait important in mate choice, even in humans. If you wonder about it, just take a piece of paper and cover the left then the right half of any person’s face. Generally you will like one half better than the other and some people have more difference between the halves than others.
What does symmetry mean for scissor-tailed flycatchers? Well, Laura and David found in the literature that young scissor-tailed flycatchers do not return to their natal lands to breed, but once they start breeding somewhere else, around half of them stick with that locations. This means they could tie birds to breeding grounds and ask about their symmetry. They measured museum specimens, so these birds had seen their last breeding season. (People used to kill birds and put them in museums all the time, but that is the topic of another entry.) Only measurements of the tail feathers showed patterns of variation with location in the range, in ways not predicted at first. Their main finding was that males showed greater asymmetry towards the center, not the edge of their range. This implies that higher quality birds, the symmetrical ones, made up more of the edge populations. Of course, in the denser central populations there were plenty of symmetrical and asymmetrical birds.
The authors interpreted this to mean that the weaker, less symmetrical birds stick around in the center of their range, but in those areas are likely to have poorer territories. In a study like this there are a lot of conditional statements. But the bottom line is there is a pattern, so further work could see if the inferences drawn from this pattern are supported. What it means for our pair or two of scissor-tailed flycatchers on Mount Doom is that they are likely to be symmetrical. I just hope they succeed in nesting sometime and are not a sink, for I love these birds.