Subject: [Tweeters] Bird population declines
Date: Jul 22 11:00:16 2006
From: Christian Kessler - northraven at cox.net


Wayne -- very interesting analysis. can you tell us how you normalized
for number of observer hours in the field? I think its fair to assume
that weather & observer competence vary randomly, but in my BBS
experience [substantial, but all in the central East Coast, I get to
join my wife in Seattle in 18 months] is that there has been a
significant increase in the number of observers and of number of
individual routes run per BBS circle. which would be expected to
produce an increase [tho perhaps small] in any species not actually
declining.

chris kessler
seattle (arriving tonight!!)
falls church, va

Wayne C. Weber wrote:
> Dennis,
>
> I have enormous respect for your knowledge and your accomplishments
> as a scientist. However, I find some of your comments about declines
> of birds and insects to be disturbingly unscientific and poorly-documented.
>
> I do not disagree with you that the net effect of human population growth
> and development on biodiversity is negative. If even a few species of
> birds or insects disappear from a large area, that is a bad thing and a
> cause for great concern. This is certainly happening in North America
> and elsewhere.
>
> However, your statement that "we're making the world worse for birds and
> other wildlife, except for a select bunch of species that are
> adapting very well to the conditions we create ..." strikes me as
> inaccurate and alarmist. For birds at least, there is a large number of
> species, not a small number of species, which have increased in
> abundance as a result of human-caused habitat changes. I can provide
> documentation for this statement.
>
> For birds in North America, one of the best indicators of population change
> is the Breeding Bird Survey, sponsored by the US Fish & Wildlife
> Service-- a project which includes numerous TWEETERS subscribers
> as participants. I looked at the latest summary of bird population changes
> in Washington on the BBS website, for the period 1968 to 2004, based on
> results from more than 90 BBS routes. These results indicate that,
> for 199 species included in the table, only 78 have shown population
> declines over this long time period, while 121 have shown increases.
>
> It should be emphasized that most of these "increases" and "decreases"
> are small, and are not statistically significant. However, even if one
> restricts
> comments to species that show statistically significant changes, in
> general the BBS shows as many species with increases as with
> decreases.
>
> Let's look at the 3 species you specifically mentioned-- Violet-green
> Swallow, Barn Swallow, and Vaux's Swift. It may be that all 3 of these
> have significantly decreased in your neighborhood, or even in greater
> Seattle overall. However, this does NOT mean that they have all
> decreased statewide. You may be unreasonably extrapolating from
> your own local area to a much larger area.
>
> Barn Swallows have definitely shown a major long-term decline in
> Washington, which is evident also in BC and probably in other nearby
> areas. For the period from 1968 to 2004, Barn Swallow populations
> have declined at a rate of 3.2 percent PER YEAR, which is
> statistically significant at the 95% level-- a shocking rate of
> decrease. (However, there are still an average of 17 Barn Swallows
> seen per BBS route-- they aren't extinct yet.)
>
> On the other hand, Violet-green Swallows have INCREASED statewide
> at an average rate of 2.0% per year. At the 95% rate, this increase is
> not statistically significant, but it is significant at the 90% level.
>
> Vaux's Swifts show a small decrease-- 0.7% per year-- which is not
> statistically significant, and may not be real.
>
> So of the 3 bird species about which you expressed concern, one
> is definitely decreasing, one is increasing, and the third shows
> no significant population change at the statewide level.
>
> I frequently hear from various long-time birders that Species X or
> Species Y, or birds in general, have dramatically decreased over
> the last 30, 40, or 50 years. However, I attribute many (not all)
> such comments to over-generalization based on a very small local
> area, or even to a faulty memory about "the old days". The role
> of declining hearing, at least, in older birders should also be
> taken into account. This almost certainly does not apply to your
> swallows and swifts, Dennis, but many supposed "declines" of birds
> described by older observers are a result of declines in their hearing,
> NOT declines of the actual birds.
>
> So Dennis, if you expect to convince us of the reality of some of these
> supposed declines, please provide better evidence in future!
>
>
> Wayne C. Weber, Ph.D.
> Delta, BC
> contopus at telus.net
>
>
>
>
>
> ----- Original Message -----
> From: "Dennis Paulson" <dennispaulson at comcast.net>
> To: "Tweeters" <tweeters at u.washington.edu>
> Sent: Friday, July 21, 2006 7:53 AM
> Subject: Re: [Tweeters] insects and swallows
>
>
> Like Diann MacRae, we have lost the Violet-green and Barn Swallows
> and Vaux's Swifts that we would see just about daily over our house
> when we first moved in here 15 years ago. I occasionally see all
> three species, but very infrequently now.
>
> It's worth considering that these species have declined (also)
> because of loss of nest sites or nest material, subtle but continuous
> changes that would be very difficult to monitor (just like insect
> abundance). Violet-greens need crevices - maybe there are fewer all
> the time. Houses are being replaced by condos, which perhaps are very
> well sealed against the outside world, as are the houses being built
> currently. Barn Swallows need mud, as well as ledges, and I've often
> thought that mud is surely declining in urban areas, as our
> surroundings are tidied up. I think both of these species have
> declined all over Seattle since I've lived here. Vaux's Swifts need
> either snags or chimneys, and the former may well be decreasing,
> especially of the size needed by the swifts, while fewer and fewer
> chimneys may present nesting opportunities because of the way they
> are constructed.
>
> It's fascinating to read the accounts of insect abundance by
> different contributors, reporting disappearances, declines,
> abundances, "too many." I would say that insects have not changed in
> abundance in my yard in 15 years, but there weren't many to begin
> with. Because of my long time spent in the East, as well as recent
> visits in summer, I will reiterate that "bugs" back there are 10x as
> abundant (and at least several times as diverse) in forested habitats
> as they are in forested habitats in the western Washington lowlands.
> In any little sunny clearing back there, you could catch or
> photograph insects for several hours and not begin to exhaust the
> species present, whereas around here I see the same small number of
> species again and again. I see in my wooded "natural" yard pretty
> much the same list of 30 or so insects and spiders that Christine
> Southwick reported in her Shoreline yard (and thank goodness there
> are at least that many), but I consider it a woefully inadequate
> representation of biodiversity, when you realize there are 91,000
> described species of insects in the US. I'm sorry I haven't had the
> time or foresight to make a continuing collection of all the insect
> species in my yard, and that would be a great project for an urban
> entomologist anywhere.
>
> But that's a digression; the same things are happening continentwide
> and worldwide. Basically, we're making the world worse for birds and
> other wildlife, except for a select bunch of species that are
> adapting very well to the conditions we create as we destroy natural
> habitats and replace them with human habitats. If we understood all
> the variables, what we see happening is probably quite to be
> expected. It should be relatively easy right now to predict which
> North American birds will still be common in 50 or 100 years!
> -----
> Dennis Paulson
> 1724 NE 98 St.
> Seattle, WA 98115
> 206-528-1382
> dennispaulson at comcast.net
>
>
>
>
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