Wednesday, August 24, 2011

August Day on Plum Island (1) REVISED FORSTER'S VS COMMON TERN

It's already late in the fall migration for many shore birds. So, when I went on a day-trip to Plum Island last week, I only saw small numbers. The beaches, that had been closed to protect nesting Piping Plovers, were soon to be opened, but a few vacationers had already made it into the restricted area at Lot # 1.

At the end of the day I came home with 400+ photos which needed to be sorted and put into neat piles of keepers and losers. Each one requires a trade-off between keeping too many and being overwhelmed, or being too thrifty and later regretting it. Best to sleep over it and leave the ultimate deleting for another day. It's late in the day, I am tired and have to be careful not to go on deleting binge as I have done before.

Now I know why:

According to a recent article in the New York Times Magazine about decision fatigue, each day we only have a limited supply of mental energy, and all decisions that we make will lower it bit by bit. Most decisions are not clear-cut Yes' or No's, but myriad Maybe's that sap our strength and render us unable to arrive at good choices at the end of the day.That's when we throw caution to the wind.  Glucose, however, partially reverses this depletion; so taking a break with a candy bar is not all bad.

Two early morning birders

I had left at 4:30 AM because I wanted to get there by 7 AM, well before the limited parking at Sandy Point at the very tip of Plum Island was filled up. Mine was the fourth car on the lot. I packed my gear and made my way down the sandy path to the beach.

There were already a couple of birders on the beach. I ran into one, who was on his way back, and couldn't let him go by without asking, "See anything? Any Forster's?"  He replied he had seen one Forster's at the very tip of the sand spit, but otherwise nothing out of the ordinary. -- I should add  here that Forster's Terns forage and breed in marshes and wetlands and are not that common right on the shore.

Small flock of Semipalmated Sandpipers flying along the water's edge.

 Although many shore birds had alreay left on their fall migration and were largely absent, there were many terns, both Common and Least.

There were lots of begging Common Tern juvies whose parents were trying to ignore them, often looking annoyed. Occasionally though one would bring a fish.

Least Terns were also there in good numbers, more juvies  than adults.

When at home I scrutinized the shot below of two flying terns I thought they looked suspiciously like Forster's, but Forster's and Common Terns are notoriously difficult to differentiate. I turned to to help with the ID. Here is the thread: According to one respondent, Smiths from Belgium, the left one was indeed a Forster's whereas the right one was a Common Tern. 

He gave a link to a sketch that helped him nail the ID. He writes:

"Based on this, the identification of the two terns in the photo becomes clearer, even though light conditions do not seem to be ideal. The left hand bird is definitely a Forster's; note extensive dark grey on central primaries, and white wedge on outers, almost like in a Black-headed Gull. Also, note bulging white loral area above bill base, and white underparts. I am not entirely sure of the right hand bird, but it looks more like a Common Tern to me: dark grey on the primaries is much more confined to the tips, there seem to be extensive grey blotches on belly and flanks, and the white loral area is much thinner."

REVISION: This can't be a Forster's tern which should show some white in the forecrown due to molt. Here is an excellent article on molts in Forster's Terns:

It was low tide and foraging on the  water-logged sandy beach was a solitary Piping Plover chick, as most adults depart on their fall migration by mid July.  It had the peculiar habit of putting one foot forward and letting it tremble in the shallow water, a behavior that I had not observed on my previous visit with Piping Plovers. It repeated the trembling with each step. According to The Shorebird Guide (O’Brien et al.) this foot-trembling feeding method causes prey to move and become more conspicuous.

View toward the public beach at Lot # 1

By afternoon all parking lots were full and there was a long line of cars  at the gate house waiting for to be admitted. It was time for me to pack up and drive home. But I'll show more photos in my next post. In the meantime head over to World Bird Wednesday at The Pine River Review for some terrific posts from all over the world.

Thanks for visiting. Please leave a comment.


  1. That looks a stunning place to go birding, and all that golden sand.
    I find some gulls and terns a nightmare to ID lol

  2. Well, you certainly had a productive day. I would never have been able to differentiate between those 2 terns. I cannot believe all that stuff that guy wrote you about! I had no idea there was such a place to get help with bird ID"s. I always lug out all my books or send a photo off to eBird for help. Well done and that piper is just the cutest thing.

    I read a really interesting article about Piping plover habitat and the whole idea of closing of beaches to protect them in the Boston Globe magazine this past Sunday. A link to the story will post on my blog this Saturday if you are interested. They talked about Plum Island and Revere Beach.

  3. Lord, the folks at Birdforum are way out of my league. I can only look at and read in wonderment a post of this magnitude. It is a pleasure to go birding with you Hilke, even if it is by laptop!

  4. Lovely photos of the beaches, shorebirds and terns. While you are seeing the shorebirds leaving on their fall migrations I am eagerly waiting for the first arriving shorebirds - it's spring down here in Australia. I expect big flocks to arrive in a week or ten days!

  5. Hilke, Only upon seeing the drawings did I fully see the differences in the 2 birds. Looks like some very knowledgeable birders at Birdforum.

    Great photos to back up your informative post!

  6. Great shots at a great place. Boom & Gary of the Vermilon River, Canada.

  7. Hilke, what a nice birdie outing. I love the terns, it is neat seeing the different species for comparison. And the Piping Plover chick is adorable, great sighting.

  8. Thank you for your thoughtful and kind comments. I just want to interject a note of caution: identifying birds on the basis of one static photo is quite unreliable, particularly in species that are so similar as the Common and the Forster's Tern. So I have no quibble with people who come to a different conclusion.

  9. a great article. And the reasoning about decisions was very good. Glad to see you kept some good wader shots. They are so cute. I can never come that close to them. :(

  10. I love the tern pics. :)

    Wildlife of California

  11. So love the terns. When we were in Florida this summer, I got similar shots. Mamas and papas were still feeding their young. It can get very noisy with their calls with fish in their beaks!

  12. Such beautiful finds! I will miss the terns and the beaches, but I gladly trade for rain and green :D

  13. Looks liek a beautiful place for sun-baking ;-) and birdwatching ;-) I love the plover pictures a lot... I guess you enjoyed the area ;-)

  14. Very interesting post and some great photos. I can relate to the point on decision making when tired as I regularly delete photos late at night only to retrieve them from the recycle bin the next day.

  15. Hi there - great shots of terns - and a wonderful account of why its not a common.

    The detail some people are able to bring to bear on bird ID is remarkable really!

    Cheers - Stewart M - Australia (where we dont have Forsters Terns!)

  16. Wonderful series. I am still learning the terns so this is very good.


  17. Awesome shots of the Terns Hilke but the Piping Plover chick steals the show for me. We have the same problem here on the west coast of trying to save the Western Snowy Plover's breeding grounds. The Mendocino Coast Audubon is doing a wonderful job through their "Save Our Shorebirds" project.

  18. The beach shot on top is so beautiful, it looks like a watercolour painting. Great photos of the birds too.

  19. Very interesting post. Great photos.

  20. Hi Hilke

    A great post. I know I can be really swamped when I come home with hundred of photos and try to decide which is better and what I should keep. We finally bought a huge extra drive for
    the computer so I can put off decision making. I loved the begging tern it really reminded me of the yound magpies we had earlier this summer.

    All the best.

  21. Wonderful post! As always your pictures are ezquisite -- and you had a great birding day, wow!

    I loved the info about decision fatigue. Having lots of pictures is both the blessing and the curse of having a digital camera.

    BTW, I would be delighted to claim your throwaways ;>)

  22. Hilke, with all the news coming out of Vermont I am thinking about you and hoping that you are okay!

  23. Thank you for all your kind words.


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