[CT Birds] kingfishers redux
elphick at sbcglobal.net
Fri Jul 25 12:30:47 EDT 2014
I've been meaning to write something about kingfishers, but Greg beat me to the punch. As a population ecologist, I would first point out that at some level ALL populations fluctuate up and down, and that these fluctuations are often especially pronounced at a local scale. It would be very surprising if there were not some species that occasionally disappeared or reappeared from a particular location in a given year. Sometimes these changes may indicate a longer term trend, but often (perhaps usually) they do not.
For example, when I moved into my current house there were mockingbirds around all the time, then there was a couple of years when there weren't any, then a few more when we saw them all the time, and now for the last year or two, they've been missing again. This is pretty normal, and probably says nothing at all about the state of mockingbird populations in the state.
That said, we should obviously be on the look out for changes that are either sustained over multiple years or that occur at lots of different places simultaneously. Greg has done a quick look at the spatial pattern, so I thought I'd address the temporal pattern as best I can.
As many of you know a few years ago Chris Field and I analyzed all of the Breeding Bird Survey (BBS) data for CT and created the ctbirdtrends.org web site. That analysis is a few years old now (sooner or later we'll find the time to update it), but it is still relevant to the longer-term trend question. If you go to the site you can create a custom trend graph for any species covered by the BBS, including kingfisher. If you'd rather cut to the chase, I've posted the trend graph for kingfisher here:
As you will see, over the 45 year period up until 2009, kingfisher counts went up and down, sometimes by a lot. Some of this might be true population changes, some of it might be "noise" in the data. (Because these are standardized counts, though the noise should be minimal, i.e., variation in observer effort should be low.) Despite these fluctuations, the bottom line is that the population size showed no evidence at all of a long term increase or decrease over this period.
Incidentally, if you're on twitter I've been posting results from the ctbirdtrends web site somewhat regularly for the past couple of months. I always use the #birdtrends hastag, so those posts are all compiled here (along with similar trend data from others):
I've fallen off on posting these results over the past month as I've been busy, but I hope to get back to posting regularly again soon.
elphick at sbcglobal.net
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