Species identification: Little Blue Heron (Egretta caerulea)
Pertinent morphology: About 60 cm tall with a wingspread of about
100 cm. The body proportions are about 1/3 head and neck, 1/3 body, and
1/3 legs and feet. The body and wing feathers are a dark, steely blue,
with a patch of dark, reddish-purple feathers on the back of the head and
upper part of the neck. There is a light patch around the eye. Some individuals
had some white feathers in patches on the wings. The beak is gray and the
legs and feet are dark gray, nearly black. The beak is straight, pointed,
and about 8 cm long. The legs are long and straight and the feet have three
long toes in front and one in back. The wings are relatively short, broad,
and rounded. When standing the body is held above the legs, without leaning
forward. The body, neck, and head are usually angled forward when walking.
Observation 1: Sunday, 31 August 2003, 1:45 pm; Hagerman National Wildlife Refuge, 20 km northwest of Sherman, Grayson Co., TX. Hagerman NWR is on the upstream part of the Big Mineral Arm of Lake Texoma.
General habitat type: The "oil jetties" area on the east side of Big Mineral Creek, bottomland which consists of a series of ponds or mudflats separated from the lake and from each other by interconnecting raised jetties and roads that lead to a series of wellheads. Whether these areas are ponds or mudflats depends on the level of the lake; most were ponds when I made these observations. The substrate is dense, silty mud that is typical of Blackland Prairie. The water in the ponds was relatively shallow and quite turbid. There were a few buttonbushes and willows alongside the jetties and a lot of giant ragweed, and some of the mudflats contained a dense stand of lotus (an aquatic plant), but there was no aquatic vegetation in the lake itself. The ponds with the lotus had areas of open water that was not covered by the plants.
Microhabitat: The road where I made this observation separates the first (northern-most) pond from the main body of the lake, and the bird was on the lake side rather than the pond side. The bird was initially standing in the water right next to the shore (about 1/2 m away from the actual bank), standing in water a few cm deep. Weather was partly cloudy, east wind 5 knots, 95oF.
Behavior: As I approached the bird crouched down, then made a
loud "squwak" as it leaped into the air and flew away. The flapping was
slow and continuous, but faster than the larger Great Blue Heron. The bird
flew up about 5 m above the water, then dropped back down and landed, again
within a meter of the shore and in shallow water, about 50 m from where
it started. When it landed, it flared the wings up and dropped the legs
down, and glided to a landing with the feet hitting just as the bird stopped.
Observation 2: Sunday, 31 August 2003, 2:05 pm; same locality as above, same general habitat as above but this time the observation was made within the northern-most pond. Same weather conditions.
Microhabitat: This bird was standing in deeper water, out in the middle of the pond. The water was deep enough to come all the way up the legs, so just the body was above water. The bird was walking along the margin of the aquatic plants about 50 meters from the closest shore.
Behavior: The bird was walking along in the water, taking a step
about once per second, but pausing for a few seconds at irregular intervals.
It also changed direction more than once, but the walking speed did not
appear to change much. The bird stayed near the aquatic plants (within
a couple of meters) and did not move out into the open water. Also it stayed
in water about the same depth as when I first observed it. While walking,
the whole bird leaned somewhat forward, the head and neck were extended
out in front, with the neck angled upward and the head tilted downward.
The head dipped down quickly into the water a couple of times. On one of
those occasions the bird extended the head upward for a second or two after
the head and neck came up out of the water.
Observation 3: Sunday, 31 August 2003, 2:30 pm;. Hagerman National Wildlife Refuge, Meadow Pond area about 3 miles south of the Big Mineral Creek bridge along the old railroad bed. Same weather conditions.
General Habitat: A flat marshy area that is part of the bottomland of Big Mineral Creek. The marsh is about 1/2 km long (north to south) and about 200 m wide (east to west). The flat marsh is lower than the surrounding terrain which is wooded; common trees include green ash, hackberry, slippery and American elm, cedar elm, and bur oak. In the marsh, some areas were covered with lotus as at the oil jetties area, and some areas were open with standing water. The middle of the marsh was open with standing water, and the margins were muddy but not covered by water. The water was shallow and turbid, and the substrate was silty and clay-rich.
Microhabitat: This depends on the particular individual observed. Most individuals were standing or walking among the aquatic plants, and some were in the open water but near the edge of the stand of aquatic plants.
Behavior: There were several individuals in this location; I
counted 11 in one scan of the marsh. These individuals were not in a flock
but were separated from one another by at least several meters. Most of
the individuals that I observed closely were either standing still in shallow
water among the lotus or were walking in the open water in the fashion
described above. In one instance I observed an individual quickly dip its
head into the water and I could clearly see it come back up with a small
fish in its bill. It then tilted the head upward (with the bill pointing
up) and swallowed the fish.
Interpretive Statement: The Little Blue Heron is a solitary, wading, fish-eating bird that prefers to forage in shallow water in flat, muddy-bottom marshes. The legs and feet are designed for wading and to give support on a muddy substrate. The long neck and long, straight, pointed bill are designed for catching fish by thrusting the head and bill into the water and grabbing a fish. The body color doesn't appear to be particularly cryptic, but when the birds are standing still in vegetation they are difficult to see. The reddish-purple color on the head and neck might be used during courtship.
The microhabitat preference while foraging might be adaptive in that it places the birds in locations that contain lots of fish. It is also possible that Little Blue Herons forage in places where they can avoid competing with larger wading, fish eating birds like the Great Egret and the Great Blue Heron. Whether competition is important in foraging microhabitat preference depends on whether food availabilty is a limiting factor for the Little Blue Heron. I have not information on the distribution and abundance of fish in the habitat where I observed the birds.
The foraging technique of walking slowly and steadily through the water presumably maximizes the rate at which the birds encounter prey items. Fish that the birds feed on might be schooling so would be in clumps rather that evenly distributed in the water. The one fish that I saw a bird eating was a small one like a minnow, so the birds probably have to eat a lot of them; most of the individual birds I saw were foraging, which may mean they spend a large proportion of their time in this activity.
These are solitary rather than flocking birds, at least while foraging. This may be adaptive because foraging individuals would interfere with each other by scaring the fish, so individuals that avoid conspecifics while foraging would be more successful foragers that individuals that do not. However, whether avoiding conspecifics is always necessary depends on the distribution of fish, which could change over time or be different in different habitats. It is possible that some sort of group foraging behavior would be favored in some habitats.