.--The Snowy Egret (Leucophoyx thula) is
well known for its diversified feeding behavior. Catching aquatic prey while in flight
has been noted by several authors. Bond (Auk, 51:500-502, 1934), Sprunt (Auk, 53:203,
1936), Grimes (Auk, 53:439, 1936) and Meyerriecks (Wilson Bull., 71:153-158, 1959)
described a feeding behavior which Meyerriecks (op. cit.:154) called "hovering-stirring."
An egret so engaged hovers near the water and with one or both feet agitates the water
or stirs vegetation or debris beneath it. I have observed Snowy Egrets using hovering-
stirring on several occasions in southern Florida. I have also witnessed a different method
of aerial feeding which may be called "foot-dragging." Employing this technique, an egret
flies just above the water with legs dangling beneath. It drags the toes of both feet
through the water and takes prey from the water while in direct flight without hovering.
I have only seen small organisms taken during such behavior and these were swallowed
while the bird was in flight. A third type of aerial feeding has been noted by Dickinson
(Auk, 64:306-307, 1947) and Jenni (Ecol. Monogr., 39:258, 1969) who reported Snowy
Egrets feeding in direct flight but without dragging their feet.
June 1972
200 THE WILSON BULLETIN Vol. a4, No. 2
I first observed foot-dragging on 22 March 1969 at a pond in the Big Cypress Swamp
of southern Florida. Additional observations were made at Mrazek Pond in Everglades
National Park on 10 December 1970. Certain conditions prevalent during the first
series of observations are pertinent in accounting for the use of such active feeding tech-
niques.
The pond, 0.25 hectares in area, is composed of two vegetation zones--a peripheral area
of emergent grass (Paspalium spp.) and a central area which during periods of high
water is filled with submerged naiad (Nctjas ]lexills). During intervals of low rainfall,
the water level in the Big Cypress Swamp drops. Fish and other aquatic organisms
become concentrated within the pond from the surrounding swamp and marshlands.
If low water levels occur at the proper time, these organisms provide a highly con-
centrated food source for numerous herons, storks and ibises which then frequent the pond.
The feeding aggregation of wading birds and other aspects of the ecology of this pond
were described by Kushlan (An ecological study of an alligator pond in the Big Cypress
Swamp of southern Florida. M.S. Thesis, University of Miami, Coral Gables, Florida.
1972, 197 pp.). On 22 March 1969 herons began to arrive at the pond at 06:10 just
after first light. Snowy Egrets first flew into the pond at 06:17 and began to feed im-
mediately; by 06:45, 450 Snowy Egrets were feeding there. These birds were dispersed
throughout the shallow emergent zone where they stood upon the trampled grass and
used stand and wait feeding behavior exclusively. By 07:00 many herons including
several hundred Snowy Egrets had left the pond. At 07:15 one Snowy Egret began
feeding using foot-dragging behavior while flying from one side of the pond to the
other. On each pass it flew low over the grass and upon reaching the open water of the
central area it began to drag its feet in the water continuing this for the length of the
pond--a distance of approximately 30 meters. Four other Snowy Egrets joined the
first and these birds fed in this manner for 10 minutes. Meanwhile other Snowy Egrets
continued to stand in the grass and although some successfully captured prey most did
not attempt to feed.
In this instance stand and wait behavior was used early in the morning when the
oxygen concentration of the water is lowest and fish are concentrated near the surface of
the pond (Kushlan, op. cit.). Snowy Egrets began to use the more active technique
when fish were less available and, from qualitative observation, success using stand
and wait behavior was limited. These observations support the contention of Meyerriecks
(Nat. Hist., 71:57, 1962) that such active feeding methods are resorted to when other
methods fail or when other areas of habitat are not productive. Further evidence is
derived from observations of Louisiana Herons (Hydranassa tricolor) at the pond.
Few were present in 1969 during the period when the wading bird aggregation actively
utilized the pond. However several fed in the pond on 30 March 1969 after the activities
of wading birds had reduced fish density (Kushlan, op cit.). At that time Louisiana
Herons along with Snowy Egrets fed by hovering-stirring almost exclusively.--JAmzS A.
KUSHLAN, Department o/ Biology, University o/ Miami, Coral Ga'bles, Florida 33214, 4
October 1971.