These are the only regularly occurring herons that are truly difficult to identify, as immatures of these two species are variable in bare-parts color and distinguishing them can require very careful study. The best clue is foraging posture, which can be seen at any distance and is very reliable. Most individuals are fairly easily separated by leg and bill color, and those differences become more obvious and more reliable over time in late fall and winter. It is perhaps only the youngest immatures in July to September that cause confusion. At least as early as March, the presence of a few new gray body feathers will distinguish most immature Little Blue Herons from the always-white Snowy Egrets.
Determining the age of a white egret can be helpful, since any white adult cannot be a Little Blue Heron, although adult Snowy Egrets have more distinctive bill and leg color than juveniles, and are less likely to cause confusion in the first place. If a bird in late summer or fall shows signs of molt (see my post on aging white egrets), or lacy plumes on the nape or back, then it must be an adult and therefore not a Little Blue Heron.
Habits and foraging posture
Little Blue Heron is a patient stalker, and walks with the neck stretched somewhat awkwardly up and forward, while the bill is pointed down at the water. This posture is distinctive. Generally solitary in shallow water, and shows a preference for grassy or weedy ponds. This species can often be seen quietly working the grassy edges of a pond while numbers of Snowy Egrets forage together in the more open water.
Snowy Egret forages in shallow water up to belly deep, rarely or never in grassy or upland situations. Typically quite active and gregarious, walking or standing with neck either stretched up or coiled, using a variety of techniques to attract or startle fish: striding purposefully through shallow water with the neck partly coiled, running through shallows with wings flapping, following flotillas of Cormorants or mergansers along creeks to catch fish that are flushed out by the diving birds. If water is too deep for standing the egrets will fly low over the surface and attempt to snatch fish from the air. This species will also crouch, with neck coiled ready to strike, and stir the water with one foot, or put the tip of the bill in the water and vibrate it to attract fish. Much of this behavior recalls Reddish Egret or Tricolored Heron, and is never engaged in by Great Egret or Little Blue Heron.
Little Blue Heron vs Snowy Egret
habits provide one of the best clues to the identity of foraging birds (see above)
wingtips show small dark gray tips on outer primaries (vs all white on Snowy Egret)
This is variable and the gray tips can be very hard to see (usually invisible when the bird is at rest) but when gray tips can be confirmed they are diagnostic for Little Blue.
legs and feet pale, chalky pea-green with feet about the same color as the legs (vs leg color generally brighter lime green with at least some black and with contrasting brighter yellow feet ).
Some young Snowy Egrets show dull green legs with no black, and even substantial amounts of black (usually on the upper front of the legs) can be difficult to see. Presence of black is diagnostic for Snowy Egret, as is contrasting yellow feet.
bill usually paler grayish with less contrasting colors, outer 30–50% of bill dark grayish, entire base of bill pale greenish-gray or fleshy gray, not contrasting much with greenish loral skin (vs bill usually darker, with blackish on culmen extending back close to forehead and pale area at base of bill clean pale gray, contrasting with fairly bright yellow-green loral skin)
But both species are variable, in particular very young birds. Both species can have the entire base of bill pinkish, yellowish, or gray (more variable in Little Blue), and both species can have contrasting yellowish loral skin (more common and more typical of Snowy Egret). Note that nestling Snowy Egrets have dark gray loral skin and some still show this color briefly after leaving tlie nest. In summary, a mostly blackish culmen is diagnostic for Snowy Egret, any other pattern can be shown by either species.
bill shape slightly deeper at base and more tapered, appearing slightly downcurved at times (vs. slightly thinner, more even depth)
This feature also leads to broader loral skin on Little Blue and more open face with staring expression (vs. narrower loral skin on Snowy Egret with more squinting or frowning expression).
Little Blue seems to have a larger eye, broader bare skin on the lores, and maybe a less pronounced eyebrow ridge above the eye; all of which leads to a more wide-eyed, “staring” expression
Many immature Little Blue Herons show a short pointed plume or two on the back of the head (vs. immature Snowy Egret lacks plumes entirely, although very young birds retain fluffy down at the tips of some head feathers; and adult Snowy Egrets have a bushy tuft of lacy plumes on the back of the head)