cause and effect speculations on some birds encoutered at 8400 ft aspen-meadow
I have had about 9 years to manage this 40 ac property. The two biggest changes were (1) eliminating grazing (it was badly over-grazed) and controlling invasive weeds (thistle, houndstongue, knapweed), and (2) a major die-off of aspen (probably 50%) due to natural causes (?, drought) with some cutting of dead trees by my partner who because of access and possibly his view of aesthetics were mostly taken within the groves where most of the aspen survive. (Surrounding, grazed aspen have befallen the same fate.)
I have lists from all my trips up there and realizing this is non-scientific, anecdotal and there are other explanations (competition, natural fluctuations in population, weather variables), I have learned the following.
Major increases in: Swainson's thrush, McGilvrey's warbler, Lincoln's sparrow, Cassin's finch--I suspect the grazing change had a hand in this as the understory is now lush.
Major decreases in: Woodpeckers (especially red-naped sapsucker), black-capped chickadees, white-breasted nuthatches. I realized the nests I've found of these birds have always been in dead trees within woods where most of the trees were alive. We've lost that habitat despite there now being more dead trees (well-popluated by PUMA, tree and v.g. swallows) overall, but these groves are all dead. I'm speculating the woodpeckers and cohorts don't like to nest in groves where there are no live trees (cover?). Plus, there have been a lot more blow-downs--mostly the old, dead trees.
Lastly, I've really populated a meadow area with nest boxes. The result has been to change the swallow mix from what I guess was about 4:1 violet-green to tree to the reverse. The tree swallows preferentially use the next boxes relative to the violet-greens.
Next year I may have a different story and explanations, but I thought this might interest some of you. Comments?
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