An important clarification on atlas safe dates:
Atlas safe dates have often been confused with breeding dates.
However, safe dates are NOT the same as breeding dates. Rather, safe
dates are established to exclude possible migrants when a bird is
seen without any evidence of nesting. The function of the safe dates
is to eliminate the possibility of saying a bird is on territory in a
block if in fact it could still be migrating.
"Safe dates" therefore may be more accurately named "non-migratory dates."
Example: a goldfinch seen on 4 June without showing any evidence of
nesting may or may not be on territory. So, it cannot be counted as a
bird on territory. After 25 June, the atlas safe date, no goldfinches
(or very few) are expected to still be migrating, and any adult bird
seen after that date can be assumed to be on territory. A goldfinch
seen carrying nest material, feeding young, etc. on 4 June, 25 June,
or any other date is an automatic breeding confirmation, regardless
of what the safe dates are. In other words, breeding can, and usually
does, happen outside of safe dates, because breeding birds and
migratory birds can overlap in time and space.
VT Breeding Bird Atlas
Date: Sun, 1 Jul 2007 19:09:01 -0400
From: Chris Petrak <[log in to unmask]>
Subject: When Do the Goldfinches breed?
I have posted on my blog (www.tailsofbirding.net) a photo of an American =
Goldfinch was taken in my back yard on June 24. The Vermont Breeding =
Bird Atlas criteria for "Safe Dates" to record the species as Possible =
or Probable are 6/25-8/1. This goldfinch has (to me) the appearance of a =
recent fledgling. Since incubation is 12-14 days and young leave the =
nest after 11-17 days, this means the parents would have begun nesting =
June 1 or earlier.
In general, I have found birds which winter in N.A. breeding 2-3 weeks =
earlier than the "safe date." Birds coming from the tropics, seems to be =
breeding closer to the "safe dates," although often exhibiting breeding =
activity a few days earlier. But I am working on impression. I have not =
analyzed my data. And to some degree, I have been restrained when doing =
the VBBA by the "safe dates." When data is entered in the VBBA data =
base, the program certainly imposed constraints.
I'm wondering if others are having similar experiences, and if the =
scientists out there are any harder data to support N.A. birds breeding =
much earlier, but not tropical birds.
It is a little late for the VBBA, but I wonder how often "Probable" =
evidence for breeding has had to be disregarded because of "Safe Dates" =
being "too" late.
South Newfane, VT
Tails of Birding - www.tailsofbirding.net