Date: 7/20/20 10:43 am From: Jane Stein <jeshawks...> Subject: Re: [VTBIRD] Hummers, they are out
Fascinating info. Thank you!
On Mon, 20 Jul 2020 17:00:49 +0000, anneboby <00000038cbe79a41-dmarc-request...> wrote: > Hello Hummer Lovers - on Fri, 7/17, I banded the first newly fledged imm. > female Ruby-throat of the season at my Adirondack banding station at Jenny > Lake in Saratoga Co., NY. Based on 29 years of banding records at this > site, this date is 3 days earlier than the previous earliest date of 7/20. > The average earliest date is 8/3, ranging as late as 8/25 in 2013. > Let me offer some further thoughts on the possibility of double brooding > based on Cornell's information that the species can be single or double > brooded. That guidance needs to be put into proper geographical > perspective. > Northward bound male Ruby-throats hit the Gulf Coast last week of Feb > based on many years of records gathered on HumNet. A few miles inland from > that coast the breeding territory of Ruby-throats begins, stretching about > 1100 mi. N into southern Canada at about 49 deg. N latitude. It is quite > possible that Ruby-throats breeding in southern U.S. states can be double > brooded if they begin breeding in Mar, but that possibility diminishes as > one goes northward. > My Jenny Lake station is at 41deg, 16 min. N latitude at an elevation of > 1250-1300 ft. Records there over 29 years show an average first banding > date of adults 5/16, range 5/6-5/24; first banding date of a newly fledged > imm. 8/3, range 7/20 (prior to this year)-8/25. The average last banding > date is 9/3, range 8/25-9/23. In 16 of the 29 years, imm. have been banded > into Sep, average last date 9/8 with dates of 12 of those 16 years > occurring 9/1-9/10. > If an average female were to double brood, she would require 3-5 days to > rehab her nest, 2 days to lay 2 eggs, 14 days to incubate and 18-23 days to > fledge a second brood, a total of 37-44 days. Based on the average date of > first banding of an imm. of 8/3, a female then attempting a second brood > would take until 9/9-9/16 to bring off that brood. This puts her brood out > of the nest past the average 9/3 departure date. > If we consider the case of the mother of the imm. I just banded on 7/17, > and apply the same breeding time table to her, she could possibly pull off > a second brood by 8/23-8/30 which, again, provides precious little time > for her newbies to develop the stamina for their upcoming over 1000-mi > migration to Central America. > At Jenny Lake, I have never seen male courting behavior after Jun. Lots > of territorial conflicts at the feeders, yes. All in all, I feel double > brooding at this latitude/elevation in the Adirondacks is not likely; the > same would apply to the Green Mountains of VT. But, we live in changing > times, including climate change and global warming which are affecting > avian time tables. We just need further proof that Ruby-throats double > brood in the mountains of the Northeast. > Bob Yunick > Jenny Lake and Schenectady, NY