[Tweeters] Swallow Numbers - Deschutes River, Oregon
johntubbs at comcast.net
johntubbs at comcast.net
Sun Aug 19 08:17:13 PDT 2018
This observation isn't regarding Washington, but relates to swallow numbers in general. With two other folks, I took 31 years of consecutive week-long float trips (ending two years ago) on the Deschutes River in Oregon (middle river, Trout Creek to Harpham Flat). In the early days of the trip, there were literally CLOUDS of swallows, Cliff most numerous, but other species as well. One year I found and photographed a juvenile Peregrine Falcon and at least one of its parents, who had obviously nested on the cliffs by White Horse Rapids that season (the parent was feeding the juvenile). The PEFA appeared to be subsisting on Cliff Swallows, whose nests were everywhere on the cliffs and fed along the river there. The PEFA would periodically stoop from the cliff top into the cloud of swallows, which was an amazing sight to watch.
There were so many swallows that occasionally one would attempt to catch the dry fly on a fly line while it was being false cast. One year one actually got mine and I had to release it (it was fine). I bring this up because on the last five to ten years of the trip, swallow numbers decreased dramatically - very dramatically. I did not take scientific observations, but the total decline was so obvious - I would estimate an order of magnitude - that it was impossible to miss. Further support for this decline was the observation of the lack of new Cliff Swallow nests on the basalt columns by the river. There are numerous places where the birds would build nests on these cliffs almost down to water level, so observation was very easy. During the period of decline, the old swallow nests deteriorated noticeably and the lack of fresh builds was apparent. I also only saw the Peregrines one year (I was told by Oregon birders that it was perhaps the first PEFA's essentially confirmed as nesting in the Deschutes canyon in some time.)
I don't know if this is a regional problem along the middle Deschutes canyon or part of a larger picture, but it was very striking and disturbing for us on the trip. With all those years of experience, being outside constantly, the wildlife rhythms of the canyon were pretty obvious. A wild card factor in the case of the Deschutes is that major changes were made fairly recently to Pelton Dam, upriver from the stretch in question, that changed the water temperature of the river and consequently decimated the previous aquatic insect profile in the river as well. That is a separate topic, and the project was designed with noble intentions, but had the effect of completely changing a long-established ecosystem (with a world class wild trout fishery) in the river below the dam. We had attributed the more recent lack of swallows to this reduction of insect life (particularly caddis species) in the river as it adjusted to the new water conditions) but it seems to me (non-scientifically) that I've noticed fewer swallows in areas other than the Deschutes as well.
It would be interesting to analyze actual long-term data where it's available - the data from the weekly walks at Nisqually NWR come to mind.
johntubbs AT comcast DOT net
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