Thursday, October 3, 2013

The Improbable Double Rare Bird Whammy

I knew it would happen sooner or later (it being me seeing a rare bird), I just didn't expect it would be in the swamp behind my house.

All of this started when I took an evening walk on Wednesday of last week. The weather was beautiful, warm for September, sunny, and was topped off with a nice light breeze. There were lots of birds flying around and I figured I might see something interesting. Perhaps I would see a new warbler species or something like that? On my way back to my house, I was walking across a grassy field next to the empty construction lot when I spotted a sparrow sitting in a bush. I took a look at it with my binoculars. 

I couldn't believe what I was seeing.
It was clearly not a Song, Swamp, Savannah, or Lincoln's Sparrow, which are all quite common right now. It also wasn't a White-Crowned, White-Throated, or a Chipping Sparrow, which are around as well (yeah, there are lots of sparrows in Peterborough this time of year). This bird had a lot of yellow on its head and immediately reminded me of the Nelson's Sparrow that I had seen in Nova Scotia earlier in the summer. I carefully approached and snapped a few photos.

Back home I inspected the photos and confirmed it was a Nelson's (and soon received an independent confirmation from a real birder. Thanks Chris R.!). That's when I looked at eBird and realized this was a very rare bird; It had only reported a few times in Peterborough. This was really exciting and I soon had submitted it to eBird, which sent out a rare bird alert. My first rare bird alert!

Nelson's Sparrow enjoying its visit to Loggerhead Swamp
The next night I took another evening swamp walk; there were still lots of birds around and it was still unseasonably nice weather. During that walk I was seeing the same set of typical birds and had started home when it occurred to me that I should probably look to see if the Nelson's Sparrow was still around. I inched forward to the bush where I saw it the night before and it flew out and ahead into the long grass of the meadow. It was still around, perhaps I could get another photo of it? That's when I noticed a different bird in the construction lot to my right.

At first I thought it was a Mourning Dove (which is what I usually see there), but when I focused in on the bird and it was clearly no dove. It was a shorebird that I hadn't seen before. I started taking photos while it nonchalantly wandered through the barren dirt lot, and it looked to me like a Black-Bellied or an American Golden Plover.

Once back at the house, I carefully examined the photos and identified it as an American Golden Plover (and once again received independent confirmation. Thanks Chris R.!). I looked on eBird and it was almost as rare as the Nelson's Sparrow. Two rare birds in two nights behind my house in Loggerhead Swamp. What are the odds?

American Golden Plover enjoying the company of a Nelson's Sparrow
After thinking about it, I wondered about the actual odds of seeing these two birds at the same time in Peterborough, Ontario. To figure this out, I looked at the number of complete check-lists reported on eBird in 2012 and 2013 by the top 100 birders in Peterborough County. The sum total is about ~13,500. Of these submissions, there were only 2 containing Nelson's Sparrows and 2 containing American Golden Plovers. The odds of seeing both birds at the same time in Peterborough would be the product of the probability of each independent event. This computes as 2/13,500 x 2/13,500 or about 1 in 45 million*. In other words, its highly improbable...perhaps a feat that will never be repeated in Peterborough! Truly an improbable double rare bird whammy. 

*This might be a bit of an underestimate as the total number of checklists for 2013 isn't yet known and will exceed the ~6500 already submitted for this year. You could also recalculate this to ask what are the odds of this happening in the month of September and the odds would be far better. This is because all of the reported sightings have been between late-August and early October, a time period that includes far less complete check-lists. Nonetheless, it remains an improbable event.

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