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