[CT Birds] Night and Day

Dennis Varza dennisvz at optonline.net
Wed Sep 8 20:05:29 EDT 2010

Hi Folks

On Sunday (5 Sep) Frank Mantlik reported a large number Laughing  
Gulls at Short Beach in the evening. When I visited Short Beach the  
next morning the gulls were gone.

To examine this phenomenon further, last night I counted the birds at  
Short Beach from the platform. This morning I repeated the count.  
(Same Location, Same Observer, Same Method, Different Time).

Stratford, Short Beach 5:00 to 7:00 Low Tide Rising
Stratford, Short Beach 7:00 to 8:00 Low tide Rising
Brant	2_0
Double-crested Cormorant	135_17
Great Egret	0_1
Snowy Egret	6_4
Black-crowned Night-Heron	0_1
Laughing Gull	70/120_7/7
Ring-billed Gull	165/5_131/3
Herring Gull	220/20_95/8
Great Black-backed Gull	13/4_15/4
Common Tern	400_275
Black Skimmer	8_8

X/Y X= birds one year old or older Y=birds that were hatched this year.

Birds on the shore, unlike land birds, are subject to two cycles,  
daylight and tides. Together they repeat roughly every two weeks. If  
it is low tide in the morning, then it will be high tide in the  
morning the next week and low again the week after that. Trying to  
sort out the influence of each is quite the challenge.

In this instance I was looking at daylight only but tide could also  
be an influence. The difference in abundance of the Laughing Gulls is  
striking. It appears that the birds come in in the evening and leave  
at first light. Ring-billed Gulls and Great black-backed Gulls on the  
other hand seem to  be resident in the area. Herring Gulls are more  
problematic. Unlike Laughing Gulls Herrings are year round  
residents.  From my Southport survey it is clear that given the same  
time of day, the birds are more common at low tide. In this situation  
I was at low tide in the evening and it started rising. In the  
morning low tide was an hour and a half earlier.   So the change in  
Herring Gulls may partially influenced by the tide.

The cormorants may be another matter. In the mourning they seem to be  
more active in feeding and the evening at roost. A Couple of days ago  
the cormorants were not on the bars or breakwater in the morning but  
up river feeding. Today the could have been there as well but not  
seen on the survey.

The Common Terns I have no feeling for. In both cases they were  
feeding heavily.

Remember, this is just one set of observation. If we had more pairs  
of surveys at different tides we could get a better handle on role of  
daylight. For the people looking for rarities, morning vs. evening  
may be an important consideration.

Dennis Varza

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