On Sun, 4 May 1997 ravenn at premier1.net wrote:

> Tweeters,
>
> I just returned from a wonderful birding trip to Texas in which I saw
> 233 species of which 31 were life birds. What an incredible area to
> bird especially during migration.

[snip]

> While at the park we met a team of people who were banding migratory
> birds...

... We never did
> understand what was being studied by banding these migratory birds. So
> now my question comes to those who have banded birds and those who have
> experience in obtaining data from banded birds. Are birds banded for
> information relating specific studies or are they banded to receive
> general information? Do we learn more from the data collected at the
> time of the banding or from if and when the bird band is recollected?
> And I would like to know what your thoughts are concerning stressing
> already exhausted birds. I'm very soft hearted and each time I saw a
> bird complete the process I was relieved to see it fly away into the
> trees.
[]
>
> Yvonne Bombardier
> Everett, Wa
> ravenn at premier1.net
>

Hi Yvonne,

You raised some good questions. If many birds were dying during handling
at the site you visited, that is disturbing, and not something I have
encountered at any banding operation I've visited. Accidents happen, and
if one out every thousand birds died during handling, I think most banders
would (while striving to reduce that number) reluctantly accept that. But
if it was a few percent or more, that's a lot. Keeping birds in cloth
bags prior to banding them is a time tested way of minimizing stress to
the bird. If a bird is caught when already on the brink of starvation, as
might happen in the with trans-gulf migrants, that presents an unusual
dilemna. On the one hand, if you're interested in what value the site has
as a stopover area where migrants can refuel, you would like to know the
condition of the birds when they arrive. On the other hand, you don't
want to harm the birds to get that data. Without knowing more details on
how many birds actually died, I'd better not speculate further.

Birds are banded both for specific studies and for "general" purposes. I
band only song sparrows, each of whom gets a unique combination of color
bands, to continue a long term study of the behavior of one population of
sparrows. I expect to see the birds I band over and over again at the
study site. Since I study behavior, the bands are a way to insure that I
can recognize individuals at a glance in the field. Although I measure
the birds when I catch them, and take a small blood sample, resightings
are where most of the data comes from.

Other banders , especially along migration routes, band all species they
catch, and use their capture data to study population trends, migration
timing and routes, and timing and patterns of molt. Unlike with the
sparrows I band, those banders don't really expect to see the birds they
band on migration again, and most of the data they get is while the bird
is still on site (although the rare distant recovery of a band is
extremely valuable).

Coincidentally I just today got the April 1997 issue of the Auk, and found
the article below, which is obviously based on a study similar to the one
you described. I typed in the abstract (summary), which, despite the
stilted prose, gives some idea what was learned.

Yong, W. and F. R. Moore. 1997. Spring stopover of intercontinental
migratory thrushes along the northern coast of the Gulf of Mexico. Auk
114:263-278

Abstract: The narrow woodlands and wooded barrier islands along the
northern coast of the Gulf of Mexico provide the first available landfall
for neotropical landbird migrants after their trans-Gulf flight. We
studied the timing, volume, fat stores, length of stay, and fat deposition
of thrushes (N=1,903) during stopover at a coastal Louisiana woodland in
1987, 1988, and 1990. Peak migration occurred around mid-April in Wood
Thrushes (_Hylocichla mustelina_) and was one to two weeks later for
_Catharus_ thrushes. More than one-third of the thrushes carried no
observable subcutaneous fat stores upon initial capture, and only 5% of
the birds had estimated fat stores that exceeded 20% of lean body mass.
Body mass and condition index (mass/wing length) were negatively related
to time of capture, suggesting that birds captured later in the day
arrived with lower fat stores. Wing size varied negatively with capture
date, suggesting differential migration between sexes and among age
classes and/or populations. Recapture probability was related to the
amount of fat stores upon initial capture, and length of stay was
predicatable from estimated fat stores, rate and amount of fat
replenishment, and capture date. Flight range estimates suggest that most
thrushes captured in spring along the northern coast of the Gulf of Mexico
are unable to reach breeding destinations in a single flight. A series of
short flights may represent a better migratory strategy than attempting
to cover the same distance in one long flight.

Chris Hill
Everett, WA
cehill at u.washington.edu