Monday, September 26, 2011

Some Slack

Biologists welcome any encounter with the animals they study, but consider themselves particularly lucky when the same individual is encountered multiple times.  The odds of a re-encounter can be improved by marking animals that reliably return to the same breeding, stop-over or wintering sites year after year. 

Breeding cliffs in Arctic spring (J. Kennedy)
A great deal has been learned about peregrines because of their tendency to behave this way.  But it takes many years, a lot of birds, huge resighting effort and persistent people to build individual encounter histories representative of the peregrines in our study.

Hilde Marie Johansen with marked adult female (A. Anctil)
For example, at Rankin Inlet this spring we captured a female (banded A|X) that is at minimum 15 or 16 years old.  First encountered in adult plumage (likely 3 or 4 at that time) in 1999, A|X has been encountered on five other occasions during her tenure at Rankin Inlet.

We know quite a bit about A|X.  Over the years she’s been paired with several different males at three different sites.   Despite her longevity and ability to hold a territory, she’s a reproductive dead-end!  We have not banded a single nestling at the sites she has occupied – she failed even to lay a single egg this year and last. 

A|X, ~15 years old, but zero young (V. l'herault)
 Like A|X, few of our breeding birds are encountered elsewhere.  We have no idea where they winter or which migratory routes they use.  More than ¾ of the annual cycle of the vast majority of the birds we study is veiled from us…this is not so with “Joe’s Hag”. 
In 2 short years, the Hag has shown us that migratory routes between years are not necessarily fixed (first through Texas in 2009 and then through Florida in 2010),  and it’s clear birds that breed at high latitudes (69°N) do not necessarily winter at low latitudes (6°).

This year she identified for us what may be the outer limits for a peregrines breeding at the northern limits of mainland Canada.  It seems the narrow margins experienced by breeders far north of the Arctic Circle have at least some slack.

Her inward migration started normally. She departed from her wintering territory in Colombia in synchrony with other peregrines wearing GPS PTTs.  Her rate of travel matched those documented previously in our study and others.  She typically stopped for 2 or 3 days after a few days of back to back passage, including a 2-day stopover on South Padre Island where she had been trapped 19 months earlier.  Everything, it seemed, was going according to plan.

Then, in early June, soon after she crossed into southern Manitoba, the Hag’s rate of travel slowed dramatically, then stopped.  And to make matters worse, her transmitter entered “Hibernation Mode”, then  stopped functioning altogether. 

As usual, most birds arrived on territory in late May, but the last signal we received from the Hag was on June 10th at a location almost 1000 miles south of her breeding location.  She was at least 2 weeks late, her 2010 eyrie was occupied by Rough Legged Hawks, and the male with which she had been paired was also absent.  We were in the dark – everything about her was veiled from us once again, perhaps for good!

Spring survey in late May as peregrines arrive to breed (V. l'herault)
The possibility of a re-encounter seemed slight, but we needed to make sure and wanted (even more) one last shot at trapping her.  Mark Prostor had put the PTT on her and he was determined to get it off if at all possible.  He and Barry Robinson set out on August 5th, when most pairs are feeding young between 10 and 14 days old.

Here’s how Mark tells the story...

Getting to the Hag’s site is no easy task.  From our field cabin, it first requires a 18 mile ride in freighter canoe followed by 10 very rough “tundra” miles on Honda ATVs just to reach the band of cliff on which she may be perched.

The Coxe Islands from the Freighter canoe (M. Fredlund
We drove the cliff base surveying for any signs of raptors. Two sites that turned out to be Rough-leg sites initially raised our hopes, but 4hrs into the search our initial expectation that she’d not made it back seemed most likely.  As we approached the end of the long band of cliff, I decided to deploy our trap in an attempt to bring any not yet seen falcons to us instead…it was a long shot, and resulted in nothing.

Rough-legged Hawk (G. Court)

With cliff and options running out fast, it seemed like a good time to do nothing at all but wait, watch and eat lunch.   The trap got no attention other than that from Barry and me.  Then, over the sound of the wind, I heard what could have been the kak-kak-kak of a peregrine. 

“Barry, did you hear that?”

We both turned and saw a male peregrine land atop a large boulder, and perched below him was a female. We had a pair of birds, and the female was wearing a PTT.  Joe’s Hag had made it back, and she was defensive! Barry searched to the east.  I had not searched far west when I found the nest ledge with three “very” young chicks…the eyes of one had not yet opened.  The Hag’s brood was 10 to 14 day younger than most of the other broods we knew of.

The day was warm, but the age of the chicks left little time to trap the Hag.  She returned to the ledge 15 minutes after Barry and I had hidden ourselves, and it took only 5 minutes more to trap her.  She was in beautiful condition with no abrasions whatsoever from wearing the harness for over a year.  But, on the patagium of her left wing was a well-healed, but still apparent injury.  Could this have slowed her down in the spring?

On the way out we drove past the cliff. She was back at the ledge with her young.  The PTT felt damn good in my pocket.