Hi Mike, Edwin and other seabirders,
Mike makes an interesting point about seabirds flying close
to shore into the wind, then doubling back fast and downwind
further out, where they can be much less detectable.
I have a couple of points to make about this. First, if they
are less detectable, how can one establish that they are
doubling back? If they are detectable, then one would surely
be able to pick out a bird as distinctive as Streaked
Shearwater even a couple of kilometres out to sea. Shore-
based seawatchers would need to be sure that the seas
further out are being watched, and they're not just
concentrating on the close birds.
It is also my experience that there are days, and not just
migration days, when the birds are streaming by in one
direction, usually associated with certain weather
conditions - unless they are doubling back way out beyond
the horizon.
The question of establishing numbers of seabirds on pelagic
boat trips is, in my experience, also a bit of a lottery.
When you have hundreds of Wedge-tailed Shearwaters around
the boat most of the day, how can you even begin to be sure
of the turnover? And I've often been surprised how high the
official count has been of some scarcer seabirds. Counting
seabirds is a very inexact science, unless perhaps if you
can get to their breeding grounds, and even there it is a
huge task.
I guess the value of counts comes if the methodology is kept
consistent, and then you're likely to at least get a sense
of seasonal, or sub-seasonal fluctations in abundance, if
not in raw numbers of birds present. There are certainly
some very clear seasonal patterns in my records of over 2
million seabirds counted from Maroubra over ten years.
Amongst those is a very clear increase in the number of
Streaked Shearwaters over that time - though I personally
never saw more than seven at one time.
Cheers,
Rod
===============================
www.birding-aus.org
birding-aus.blogspot.com
To unsubscribe from this mailing list,
send the message:
unsubscribe
(in the body of the message, with no Subject line)
to:
===============================
|
