[CT Birds] Night and Day
dennisvz at optonline.net
Wed Sep 8 20:05:29 EDT 2010
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
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
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.
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