Date: 5/2/18 8:07 pm
From: Peter Reisfeld <drpinky...>
Subject: [nysbirds-l] Radar musings


The radar pattern tonight is similar to what it was last night.  High reflectivity and high velocity in a NW direction.  Does this mean tomorrow will be birdy or quiet? I can’t say for sure but I’d like to share some thoughts about it.  

Steve brings up the issue of promising radar reports but poor showings on the ground.  The mediocre showing today despite high reflectivity on radar is a phenomenon I have seen a number of times before. It has been my impression that this occurs more frequently on nights when migration velocity is high.  I have never seen an explanation for it, but thinking about it today, a theory occurred to me.  

To illustrate the theory, I’d like to use the analogy of rain on a windshield.  Whenever I am driving on the highway in the rain, the faster I drive, the harder it seems to rain.  While driving fast does not increase the density of raindrops falling from the sky, it does cause many more drops to hit the windshield per second as you drive into a steadily falling stream.

Perhaps it is the same with bird radar.  When birds are flying particularly rapidly, more of them may intersect with the radar beam per second.  This produces an increase in reflectivity, without an increase in density of birds.  Since we generally assume that high reflectivity is due to high bird density, the spurious increased reflectivity would make it seem that more birds were up there than really were. Hence a disapointing showing on the ground the next morning. This scenario could explain what happened last night.

While I have not heard of this theory before, I doubt I am the first to think of it.  I emailed Cape May radar-maven David La Puma about it today. If he gets back to me, I’ll let you know what he thinks.
So what about tomorrow?  I would just say this.  Birds are up there and migrating rapidly.  It's just that the numbers MAY NOT be as high as it appears based on reflectivities. 


In any case, good luck out there,


Peter

 

On Wednesday, May 2, 2018, 7:17:58 PM EDT, Shaibal Mitra <Shaibal.Mitra...> wrote:

Hi Steve and all,

At Robert Moses SP, to the east of Jones beach, I didn't see any Red-headed Woodpeckers this morning, but I did see 14 Red-bellied Woodpeckers--all migrating east to west. Those familiar with the barrier beaches, and the usual absence of most forest "resident" species there, will understand that this was a remarkable sight. Stephane Perrault has some interesting ideas on the relationship between these irruptive flights and inter-year variations in the regional population density.

Southwest winds tonight?--let's get some more Melanerpes data!

Shai Mitra
Bay Shore
________________________________________
From: <bounce-122535933-11143133...> [<bounce-122535933-11143133...>] on behalf of Steve Walter [<swalter15...>]
Sent: Wednesday, May 2, 2018 7:09 PM
To: NYSBIRDS
Subject: [nysbirds-l] Red-headed Woodpeckers at Jones Beach

I had two adult Red-headed Woodpeckers at Jones Beach West End this morning, essentially as fly-bys. The first flew by me while I was in the median and turned east on the blind side of the tree line. The second, about a minute later, made brief stops in the higher trees before also moving east and out of sight. Also, one or two Red-bellied Woodpeckers were around. So it was Melanerpes Moving Day.

I hadn’t planned on going down to the beach, but an early assessment of the Queens parks suggested the much anticipated and overdue first big wave had not materialized – at least not here. I’ve gotten into the radar watching, like others have.  I can’t say that I feel comfortable with what I see – but. The other day, someone mentioned the radar showing birds. Looking at the referenced radar image, it didn’t look that way to me. But I do appreciate people looking at that and offering alerts or opinions. We might figure this out. What I looked at on radar this morning suggested there was movement along the coast. So I figured why not change plans and check that out. I can’t say that what I saw on the ground should have lit up the radar, but there were a variety of migrants at Jones. Not much unusual other than the woodpeckers, but 5 Baltimore Orioles in one tree was a sight to see. Maybe the most interesting bird I came across was an immature Great Cormorant on a piling outside the boat basin. It doesn’t look like a record late date, but close as far I can see.

So what happened with the migration? It’s May 2, there was no flight of note recently, and winds last night were SW to WSW. There should have been migrants everywhere. One thing I had been noting and saying to people is that the trees have barely begun to leaf out – which would also limit insect hatches. Arboreal birds don’t want to be in that. Would that retard the migration? Wouldn’t they actually have to get here to know what the situation is here? Well, SW again tonight. It can only get better.


Steve Walter
Bayside, NY
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