Sunday, June 2, 2013

Coincidence - maybe not.

Watching “Island Girl” (a female Peregrine Falcon tagged by FRG in 2009) migrate northward for the 5th consecutive year, it's difficult not to be charmed by her.  By combining efforts across research teams, she and other PTT- or otherwise-tagged birds have disclosed a few more of the nifty migratory tricks used by peregrines flying to and from the breeding grounds.

Small samples have a nasty way of revealing enough information to get folks all hot and bothered, and subsequently flustered when seemingly clear patterns turn out to be no more than mere coincidence when viewed in the context of larger samples.   But just for fun, Mark Prostor (who is a big part of the Arctic Raptors research crew) compared the relative positions of “Island Girl” and “64493” (a PTT-tagged peregrine in 2011 by Arctic Raptors) as they make a final push for their respective breeding territories on Baffin Island and the Melville Peninsular (near Igloolik, Nunavut).

PTT data showed that both birds paused this last week, and despite being more than 700km apart, when viewed in the context of MODIS near-real-time satellite imagery, their stop locations coincided with the snow-line which tends southward nearer to the Hudson Bay and James Bay.  Taking the stop location of each bird relative to their known destinations revealed additional similarities;  both birds positioned themselves at the snowline about 1300km direct line of flight to their breeding sites at remarkably similar compass headings (about 50 degrees).
Stop-locations of "Island Girl" (red) and "64494" (blue) at the snow line (white arc). Note the parallel compass headings (about 50 degrees) from their relative stop-locations at the snow line;  at the time (May 31) both birds had about 1300km to reach their respective nesting location; both birds took a northwest heading near the US/Canada border before resuming their flight to the northeast. 
Earlier flight paths showed another similarity;  both birds veered northwest near the US/Canada border rather than simply maintaining a northeast heading which would have taken them on a much more direct route towards their breeding locations.

Incidentally, both birds will also arrive much later than other tundra peregrines.   Despite extensive snow cover, our spring survey at Rankin Inlet showed that most breeding sites were occupied by pairs by May 22, and tracking by light-based geolocators (which weigh 1 gram) showed that arrival of some birds at Rankin Inlet was as early as May 20.  Breeding latitude likely plays a part (both “Island Girl” and “64493” have further to go than birds breeding at Rankin Inlet) in the explaining the difference.  However, our field crews trapped birds on territory near Igloolik on May 28th.  While it could be coincidence that both PTT-wearing birds will arrive late, just maybe it’s not.

Snow covered sea-ice at Rankin Inlet with Barrier Island cliffs on right.  The region received almost a meter of snow in 3 days less than a week before peregrines arrived on territory.  (Photo E. Hedlin)

Saturday, March 16, 2013

"You ain't in Kansas, neither"

On August 19 2010, a 36 day old male Peregrine Falcon that had previously been marked with a colored leg band (25 A) was seen flying from its natal site.  It was later "camera trapped" at a neighboring nest site that contained 2 other nestlings (27 A and 73 E).  Motion sensitive camera images showed that the adopted nestling remained at the neighboring site for several days during which time it shared the nest ledge with the two resident nestlings and was fed by the adults that occupied the site.   The juvenile falcon then returned to its natal site where it again shared the nest ledge with its natural sibling and received care from its natural parents.
A full decription of the observation has been accepted for publication and will appear in the June 2013 issue of Arctic, the following images complement the note.
Images are generally only a few seconds apart, but check the top left corner of each image for time-stamps.  Temperature is recorded in the top right corner and site number in lower left (Click on images for larger versions).

  25 A at adopted site with 27 A and 73 E within 3 hours of leaving his natal site on August 19.
27 A and 73 E spent the night of August 19 alone on the nest ledge

Adult female feeding all three nestligs

27 A and 73 E  spent several hours alone on the nest ledge; then when the adult female returned to the nest approximately five hours later with another prey item, 25 A quickly returned to the ledge.

Adult female deivers a prey item

On August 20 and August 21, the adult female resident at Site 28 delivered prey items on 4 more occasions. Each time 25 A was present on the nest ledge with the resident nestlings and competed for a share of the prey item that was delivered. An adult and the adopted nestling were observed together on the nest ledge at Site 28 on August 23, more than 3 days after flying from its natal site (Site 29).

At Site 29 on August 24 in the morning, an adult falcon delivered a prey item to 62 E (the natural sibling of 25 A); within a few seconds 25 A appeared on the ledge at Site 29 with 62 E after spending nearly five full days away from the site. 

The following day, the resident adults at Site 29 made several prey deliveries which were mostly consumed and cached by 62 E. However, photographs of 25 A indicated that the male was on the nest ledge at least twice that day, and clearly showed that 25 A either consumed or shared prey items that had been previously cached by 62 E.