Subject: [Tweeters] Breeding Bird Survey population trends
Date: Jul 22 16:39:01 2006
From: Wayne C. Weber - contopus at telus.net


Christian, Dennis, and Tweeters,

I didn't do the Breeding Bird Survey trend analyses-- they were done
by staff of the US Geological Survey. The results are posted on
the Internet for anyone to see. Trend analyses for Washington are at
http://www.mbr-pwrc.usgs.gov/cgi-bin/atlasa99.pl?WAS&2&04 .
Results for any other state, for individual ecogeographic regions, or
for areas as large as all of the US or all of North America can also
be viewed at this website.

Since I didn't do the analyses, I cannot comment in detail on the
methodology. However, I can say that analysis and interpretation
of BBS results is a complex subject, and required development of new
statistical methods. The primary method of analysis has changed 3
or 4 times since analyses were started, and I believe that several graduate
theses in statistics have been written on the subject.

In a nutshell, BBS data are used in trend analyses only where data
were recorded in both years. I.e., changes for 1990 to 1991 are based
only on routes that were covered in both those years; the same for
1991 to 1992, etc.

The long-term trends do not simply compare numbers recorded in
1968 with those recorded in 2004. I believe they are based on
the year-to-year changes in each pair of years over the time
period (e.g. 1968-1969, 1969-1970, 1970-1971, etc.) If the trends were
downward in 27 of the 35 individual pairs of years, it is likely that the
long-term trend would be a significant decrease (using 95%
confidence intervals). On the other hand, if there were declines in
17 of the pairs of years and increases in 18, it is likely that the
long-term trend would be one of no significant change.

Interpreting results of BBS trend analyses is as complicated as
doing the analyses. For species that are rare, highly gregarious, or
crepuscular (e.g. owls or nighthawks), results are much less reliable
than for widely-distributed songbirds. In general, the commoner and more
widespread a species is, the better the likelihood that the BBS
can detect a significant population change.

Have a look at the Washington page. You will find the data intriguing.
Some of them may confirm your subjective impressions, whereas
others may not. The webpage shows population trends for 3
time intervals: 1966-2004, 1966-1979, and 1980-2004. However, the first
BBS routes in Washington were not run until 1968, so the results for WA
are really for 1968-2004 and 1968-1979.

I have covered 3 BBS routes myself in the Nicola Valley of BC most
years since 1980 (and 2 of them since 1974). (In addition, I did one
route in Greater Vancouver from 1974 to 1994, but have since abandoned
it since traffic makes it nearly impossible to cover properly now.)
The long-term trends from these 3 routes are fascinating, and in many
cases agree with province-wide or region-wide population trends. The value
of BBS data in determining long-term population trends, and in pointing out
possible conservation problems, cannot be overstated.


Wayne C. Weber
Delta, BC
contopus at telus.net



----- Original Message -----
From: "Christian Kessler" <northraven at cox.net>
To: "Wayne C. Weber" <contopus at telus.net>
Cc: "Dennis Paulson" <dennispaulson at comcast.net>; "TWEETERS"
<tweeters at u.washington.edu>
Sent: Saturday, July 22, 2006 11:00 AM
Subject: Re: [Tweeters] Bird population declines


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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