Subject: Re: Contents of Journal of Field Ornithology, Vol 67 No 2, Spring 1996 (fwd)
Date: Apr 27 10:24:43 1996
From: "M. Smith" - whimbrel at u.washington.edu


I don't think this made it to tweeters.

-------------
Michael R. Smith
Univ. of Washington, Seattle
whimbrel at u.washington.edu
http://salmo.cqs.washington.edu/~wagap/mike.html

---------- Forwarded message ----------
Date: Fri, 26 Apr 96 14:11:11 MDT
From: Dorothy Phyllis Hill <dphill at acs.ucalgary.ca>
To: whimbrel at u.washington.edu
Subject: Re: Contents of Journal of Field Ornithology, Vol 67 No 2, Spring 1996

Dear Micheal Smith and Tweeters:

I recieved your questions about our paper on nest visitation
and predation rates on Chestnut-collared Longspur eggs and young,
and am most happy to answer your questions.
First, you make a very good point that our title can be
misleading. This is something we were unaware of and, from your
comments, I suspect a better title would have been "Frequency of
nest visitation by humans does not increase predation on
Chestnut-collared Longspur eggs and young". In this paper, we
examined whether visiting a nest more frequently made it more
vulnerable to predation than a nest visited less frequently.
Other studies have found that some predators will "cue in" on
signs left by human visitors resulting in increasing predation
rates with increasing nest visitation. As you pointed out, it is
impossible to examine visitation vs. no visitation; similarily it
is impossible to conduct a nesting study without visiting the
nest. We chose 3 nest visitation frequencies that we felt could
be readily used by researchers conducting an intensive nesting
study without loosing information (for example, by having the
young fledge before they are banded, etc.). Something that made
our study a little different from other studies is that we
assigned these visitation rates randomly - in many studies, nest
are visited at different frequencies because the researchers
simply don't have time to visit each nest every day.
Our results surprised us. Not only did we find no
statistically significant difference in predation rates between
the different visitation groups, but there was a trend that nests
visited every 4 days (less frequently) were preyed on MORE than
nests visited every day or every second day! In other words, it
appeared that nest visitation by humans may have been decreasing
predation. (For those of you who do not have a statistics
background, a trend is not statistically significant, but may be
of biological importance; in our case, if we had a sample size 6
times larger but with the same relative porprotions, it would
have been a statistical difference). This may not be as bizarre
as it sounds because Gotmark (1992) in his review found that
human scent can scare some mammalian predators away from an
area. Our study area is a ranching/farming area where many
potential nest predators like coyotes and skunks are commonly
shot at. This is why we said that it was clear that visitation
(frequency) did not increase predation, but we unable to say for
certain whether visitation had no effect or actually decreased
the predation rate.
One thing that we did not want to do was give the impression
that no one need worry anymore about the effects of nest
visitation. We had an eco-tour operator comment on our poster at
conference - he said that now he won't feel guilty allowing
groups of 10-15 people to photograph at a nest! As Michael Smith
pointed out, even the first visit may have a very big impact, but
we have no way of knowing that. Also, when avian predators are the
main predators, predation rates often increase with visitation
frequency. The aim of our study was to examine whether
researchers should visit Chestnut-collared Longspur nests less
frequently to reduce some of the impact they have in conducting
their studies.
If any of you have more questions about our study or its
implications, please do not hesitate to send them to me. I'm
glad that there's so much interest! Also, I'm interested in
hearing more about "Mont lake Phil". Did anyone write up that
sighting? I'd like to read it. Thanks!


Yours sincerely,



Dorothy Hill