Chirs and other Vermont Atlasers,
We have been enjoying everyone's tales of atlas discoveries from afar.
Safe dates occasionally caused some confusion and discussion on the
recently-completed Maryland/D.C. Atlas as well and we can offer the
following comments. The dates listed as "safe" are not breeding season
dates, but migration/dispersal dates, which overlap a species' breeding
season. For most migratory species, atlasers may encounter either
migrating _or_ breeding individuals early or late in the nesting season.
Safe dates indicate when almost all migrants have reached (or have
started to disperse from) their breeding grounds. Birds encountered in
appropriate habitat, without other breeding evidence, within those dates
can be considered possible breeders. Many individual birds start nesting
ahead of the safe dates for their species and can be found exhibiting
probable or confirmed breeding behavior while some more northerly
nesting individuals of the same species are still on passage.
The goldfinch in question is an adult female, looking fluffy because she
appears to be sunning. Juvenile goldfinches are rich buff, including
noticeable broad buffy wing bars, with a dark bill. Here in Maryland,
there does seem to be a trend toward earlier nesting by goldfinches,
perhaps in response to an early-blooming introduced thistle or warming
climate influencing an earlier blooming season for Canada thistle.
Chris's impression regarding the relative starts of breeding for North
American-wintering vs. tropical-wintering species is probably fairly
accurate - in general, species wintering on the continent have a more
prolonged migration than those coming from a greater distance - time is
of the essence when there is more ground to cover.
Enjoy your atlassing,
Walter Ellison & Nancy Martin
Chris Petrak wrote:
> 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.
> Chris Petrak
> South Newfane, VT
> Tails of Birding - www.tailsofbirding.net