Brian Gates says:

> Nevertheless, many samples taken over many years, under varied weather
> conditions and by a broad mixture of observers can be meaningful...if they
> are interpreted properly. If, from CBC results, a species appears to be
> in decline, that's when the scientists should move in, set up controlled
> studies and test to see if the trend is real. If it is, then conservation
> programs must be initiated. The CBC results cannot be the end point in
> themselves.

I disagree with Brian here in at least one detail. I think he is too
cautious in suggesting that trends in CBC data need to be tested to see if
they are "real," with only a two minor exceptions. Certain groups provide
ID challenges - the data on them may be unreliable until these challenges
are overcome, especially if the confused parties include the compilers. I
would argue that even here, the flawed nature of the data is usually
conspicuous to anyone who compares totals from counts within a region.
Illogical patterns of distribution (e.g. adjacent coastal counts, one of
which reports 60% of the gulls as hybrids, while the other reports no
hybrids) are a good tipoff. For uncommon and elusive birds, such as
Saw-whet Owls, the numbers found are too small and variable a proportion
of the population to provide meaningful data, at least until techniques
like playback become a consistent part of counter's arsenals. But for
the vast majority of birds, the trends in CBC data are clear and easily
interpretable, and the counts are surprisingly sensitive to changes in
bird populations.


I'll give an example from New England. I compiled a count in MA for four
years, so I have paid quite a bit of attention to the data that resulted,
and one of the more instructive cases is that of the Northern Shrike.
This is a bird that is never common, and varies greatly in abundance. It
would be extremely hard to get a reliable and quantitative estimate of
Shrike density working alone. Even, or especially, for "scientists,
conducting controlled studies." In some years, there are "none" around,
in other years, some shrikes are found, and if there is a good local
grapevine, you might hear about several over the course of a winter. It
is unlikely that even in a "good" winter for shrikes, anyone would find
more than a couple on his or her own, even if they birded every weekend.
Quite possibly they might not see any, if noone told them where
already-located birds were located. So here you have an uncommon,
unpredictable, somewhat hard to locate bird - much harder to count than
most birds.

To cut to the chase, when there was an invasion of shrikes, or harriers,
or rough-legged hawks, as signalled by maybe only one or two reports in
two months on the *excellent* birding grapevine in this particular area,
CBC results showed it clearly. One year we heard maybe 3 scattered
reports of N. Shrikes during late fall; the local CBC picked up 7 (most
years, none are found). A nearby count with much less coverage (maybe 15
observers, as opposed to our 65), and with much less open habitat, also
found two shrikes. The count to the north of us had shrikes. The count
to the east of us, in a 90% wooded circle, had a shrike. Everywhere you
looked in Southern New England, these birds were being found, even though
there were very few out there in absolute numbers (even 7 in the 177 sq.
miles of a count circle is *not many*). And they were being found in
rough proportion to the amount of good habitat in the count circles. So
if Blue Jays decline from 4000 to 500 on a count (and common bird numbers
do fluctuate like that without anyone noticing) you can bet the change is
real.

[I had better insert a disclaimer here to the screed that follows: My
direct contact with the people at American Birds, most of whom I liked
very much personally, ended in 1991. So what I have to say below may no
longer apply. But as a statement of the situation as I saw it in '86-'91,
I will stand by the following]

OK, time to wind it up. My theory for the persistence of the idea that
these counts are basically unreliable is that no one knows what a goldmine
they are, because very few people take the time to find out. They don't
use the data because it is very *hard* to, as anyone who has tried can
attest. You have to wade through volumes and volumes, scanning fine print
on THOUSANDS of pages to get the data you want to answer a particular
question.


And why is the data so hard to use? Well, I think part of the blame has
to go to the folks at American Birds. I can't blame individual birders
for caring mostly about finding rarities, in fact it probably means they
do an all-around better job at covering and counting an area. But I can
blame American Birds for overemphasizing the recreational side of the
count and ignoring their responsibility to encourage use of the data.
They tried one year to put the data in more accessible form (tables),
which was great, and then immediately backpedalled when they got letters
protesting that they were violating tradition or integrity or something.
The next year, I think it was, they skipped all the regional summaries
which help to point out trends, and gave us only a few pages, telling us
which counts had the most species in the US, in the world, had the most
participants, had the most feeder-watchers... I think those who do suspect
a cheapening of the motivations of counters in the field (and I am
emphatically *not* among them) should start at the top when they look for
explanations of why.

Someone needs to explain the concept of "electronic database" to the
people at the National Audubon Society. I would be much happier giving
my 5$ fee, and collecting it from others, if I weren't suspicious that
NAS was concerned more with fundraising than with science.

Well, to quote Richard Dawkins "Now, I'd better go out and dig the
garden, or something."


Chris (I *really* should be working on my Master's thesis) Hill
Seattle, WA
cehill at u.washington.edu