Monday, September 30, 2013

The Eagle has landed: 'southern' Bald Eagle dispersal in spring

Juvenile Bald Eagle - Joseph Stevenson
'Southern' Bald Eagle migration. It’s a phenomenon that spring hawkwatches, especially along the great lakes, look forward to for late season excitement. I distinctly remember my first major flight at Braddock on May 29th 2011 when an incredible 94 individual Bald Eagles soared past me on the day – including kettles of eagles up to nine strong and an hour where 63 birds were tallied.

Though even relatively recently I have had experienced hawkwatchers question me about the veracity of the phenomenon, it was back in the mid eighties that experienced hawkwatchers like Frank Nicoletti started to note the occurrence of these flights. As the story was related to me, during his first seasons tenure at Braddock Bay Frank noticed that a lot of the late season birds they were seeing looked like small (see Bergmann's rule), crisp and extensively dark hatch year birds – unlike the bleached and worn juveniles one would expect to see if they had hatched the previous year. Apparently he stated immediately that he believed these were hatch year birds from Florida and other Southern States.

Juvenile Bald Eagle - Joseph Stevenson
During an average season one can view this kind of flight reflected on the HMANA Hawkcount website in May at Braddock Bay (for example). In fact these flights can often be seen moving over watches into June after the official end to the season at places like Braddock and Derby Hill and those eagles can often make up a significant percentage of those days flights (example here). 

Personally, whilst counting at Braddock, I had noted up that some of the birds arriving with the Broad-wings in mid-April also appeared to have this smaller, darker, crisp appearance. It seemed to me impossible that these could be southern birds though just due to the early timing, but they sure looked right for them. That, however, would mean birds, just a couple of months out of the nest, had made it the 1000-1500 miles all the way from Southern Florida up to Rochester; it just seemed too incredible to imagine.

Juvenile Bald Eagle - Joseph Stevenson
A little research though seemed to back up the possibility, as according to the USFWS Bald Eagle egg-laying can begin during October. Given a four and a half month cycle until fledging and then a few extra weeks spent around the nest that would seem to point to the potential dispersal of these young eagles during late March. To witness this early breeding in action you can follow the nestcam of a Bald Eagle in Southwestern Florida (here), you can also see updates on their exceptionally popular facebook page (here). The feed starts in just a day or two on October 1st.

These theories at Braddock got the support of some hard evidence this year for the first time. On April 13th one of BBRR’s stalwart banders, Dan Niven, captured a Bald Eagle at the Braddock Bay Raptor Research main blind that was already sporting a band. This was exciting enough in and of itself, but when the report was received from the bird banding lab we discovered something incredible and important, that the bird had been banded as a hatch year bird on February 5th down in Florida (coincidentally enough by ex-BBRR bander John Newhouse). Here was definitive proof that birds that hatched that same year in Florida could make it up to Braddock Bay by mid-April as part of their dispersal.

'Southern' Bald Eagles had initially been believed to be a sedentary subspecies until banders in Florida started to actively band them. Returns of these bands showed that these birds were heading north for the summer. Check out this awesome article (here) from 1947 that Rick Wright brought to my attention after reading this post. Note firstly how far north these banded birds were recovered: PEI, New Brunswick and Nova Scotia and secondly, sadly, the number recovered dead after being shot (even though the Bald Eagle Protection Act had been passed in 1940).

Juvenile Bald Eagle - Joseph Stevenson
This northbound dispersal, to me, underlines the incredible feats these birds perform and just another reason to be in awe of them. If you want to come see some of these 'southern' Bald Eagles fly, come join The Hawk Migration Association of North America and Frank Nicoletti for their Raptor ID Workshop up at Braddock Bay in early April 2014 (link here) or for HMANA's 40th Anniversary Conference in the same location later in the month (link here).

Thanks to Joseph Stevenson for the photographs of the event.

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