Monday, September 14, 2015

Birds migrate, eBirders count!

And it is again the time of the year where some impressive flocks of migrant birds can be seen in the sky on their annual southbound passage to South America through the Panama isthmus.  This is certainly true for the daylight migrants, like the raptors.  Since yesterday, some impressive flocks of both Plumbeous and Mississippi Kites have crossed Panama City's skies... although few Panamanians are aware of that.  For me, it was kind of special because I recorded for the first time a flock of Swallow-tailed Kites from my balcony.
Swallow-tailed Kites
Swallow-tailed Kite
Yes, now my balcony list stands at 118 species!  Just second before I recorded a huge flock of Plumbeous Kites that were new for my list too.  These birds approached from the southwest, took the thermal current very close to my apartment (thus I was able to see the black tails with white bars and the rufous primaries) and leave it very high flying eastward.
Plumbeous Kite
However, today was truly spectacular... at first, a little flock of 50 Plumbeous Kites flew low enough to see the same field marks I witnessed yesterday; then, a second group follow them with some Black Vultures... however, this were congeneric Mississippi Kites.  Notice the pale heads and pale secondaries of these birds.
Mississippi Kites and Black Vultures
While seeing this second flock, I noticed some "tiny spots" in the background.  After focusing it properly, I realized the these "tiny spots" were thousands of kites very high in the sky... too high to ID properly to species.  They were Ictinia kites for sure.  Immediately, I started to estimate the number of individuals in this Mississippi/Plumbeous Kites flock.  First, I quickly counted 100 individuals, got a sense of the proportion of the flock they take up and then extrapolated by hundreds the rest of the flock.  My estimation was 6000 birds.  It sounds straight forward... but it needs some practice; however, after a while you will make it automatically.  A very interesting article about counting birds can be found in the eBird main (or just click HERE).  Of course, to use this method you need a fairly uniform flock of the same species/group.  For example, this photo shows approximately one third of the flock I saw today:
All those dots are Mississippi Kites, with at least three Black Vultures mixed in (you may need to enlarge the photo)
For purely educational purposes, I divided this photo into four equal parts and counted individuals in one of these parties (which represent 1/12 of the original flock).  Do not pay attention to the size and shape of the red circles ... I only drew them for not count the same individual two or three or ten times!
533 Mississippi/Plumbeous Kites (and a Black Vulture); thus, a flock of 6396 individuals (533 x 12)
I did the same with the next picture, which I took with a larger zoom, and representing approximately one tenth of the flock:
Many Mississippi/Plumbeous Kites
578 Mississippi/Plumbeous Kites; thus, a flock of 5780 birds (578 x 10)
Using both estimates, I calculated an average: 6,088 Mississippi/Plumbeous Kites in that single flock (6396 + 5780 / 2).  That's why I wrote down that number in my eBird checklist and not my first estimate of 6000 birds... although they are pretty similar!  So what are you waiting for... it is time to practice and to look up for migrant flocks of birds!

1 comment:

  1. this is such a fantastic time in the year, thank you for your post, I did enjoy it! I wish I had more time to visit Panama city and see the birds there...well you can only so much...