Monday, July 31, 2017

Watching the tide herons

Call them the tide-herons.

After hearing from a local resident who mentioned he had seen Yellow-crowned Night-Herons in his own little patch in an out-of-the-way park on the East River, I began thinking Clason Point Park or Soundview Park might be the lone or one of the few Bronx spots to potentially see the species. I know very little of this species beyond identification, so my guesses as to when to see it centered on "anything is possible during migration" or the possibility that they nested locally.

In scanning information about their behavior, I found the following clue on Cornell University Lab of Ornithology to help me narrow it down:

"Yellow-crowned night-herons forage both during the day and the night - in coastal areas the tide can trump the time of day: most foraging occurs from 3 hours before high tide to 3 hours after."

High tide near the mouth of the Bronx River

Low tide near the mouth of the Bronx River

Limited to pretty much weekends and public transit, and with a fellow bird watcher who has unique requirements, following the tides is bit a of a challenge. Nonetheless, the chance at seeing this species would be worth the multiple buses it would take to get there.

Indeed it has been.

We found Yellow-crowned Night-Herons. And not just one and not just one time.

Two Yellow-crowned Night-Herons flying in at low tide.

I have found their arrival and departure to perhaps follow the opposite pattern as the clue above, albeit with a limited sample of observations, where they follow the low tide. Not suggesting the Cornell piece is wrong, just that in this case, if I want to see the night-herons, low tide is the time to visit.

The water level drops around six to eight feet at low tide and multiple foraging locations open up in the hours as the tide ebbs. At high tide, the river swells back around six to eight feet higher, covering the muddy areas and creeping up into the big rocks on the side. This area does not seem to be as useful to these herons at and around high tide. Multiple tide charts can be found, but I find this one to be most useful:

Great Blue Heron (far left), four Black-crowned Night-herons,
two Yellow-crowned Night-Herons, a Ring-billed Gull,
and a Mallard forage at low tide.

Yellow-crowned Night-Heron (left) and Black-crowned
Night-Heron (right) on exposed rocks at low tide.

I wonder if on the other low tide this group of herons also returns. The other low tide will generally be at night and thus not accessible to view from an NYC park (or easy to view in the dark). And what do they do the rest of the time? Rest? Forage elsewhere? And where?

Yellow-crowned Night-Heron (left) and Snowy Egret (right)
at low tide.

Great Egret (back left), four Yellow-crowned Night-Herons,
and two Black-crowned Night-Herons at low tide.

As the tide flowed up river, I watched one adult Yellow-crowned Night-Heron take off and fly east along the southern bank of the Bronx River. As it neared what appeared to be a point (the land juts south), it lifted, gaining elevation and then heading due south. It was now just a spec unrecognizable between the other bird specs. Did it continue south? Did it head to the Brother Islands where Audubon Harbor Herons has found nests in previous years? Or head east? Does it have a nest? Are there more of them, beyond the high count of eight that I observed this summer, that perhaps go feed in another favorable location?

A Yellow-crowned Night-Heron took to a tree on the opposite
bank as the tide rolled in.

Without a boat and probably a lot of time, I won't know the answers to these questions. I do know that my time with these birds is determined by the rising and falling of sea levels from the gravitational pull of the moon. And I know when I can visit them by checking a schedule of the tides. Call them the tide-herons.

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