Sunday, July 01, 2007

When do goldfinches start to breed?

This photo of the 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. Incubation is 12-14 days. Young leave nest 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.


Anonymous said...

My understanding of Safe Dates for the PA Breeding Bird Atlas is that birds can breed outside of Safe Dates but outside of safe dates you can't assume the particular species is probably breeding (as some birds of that species are still on the move) unless you have firm evidence like nest building, carrying food and the like. In Pennsylvannia a bird can be confirmed outside of safe dates as long as there is firm evidence. An example is that I confirmed Blue Jays in one of my blocks even though they were outside of safe dates as I found one feeding its young. So while there are some constraints in PA too, they seem to have some flexability. May more than Vermont?

Anonymous said...

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Nick said...

I'm writing from Italy, typically goldfinches start nesting since half May until half July, this match with your observations.


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