Hidden beneath the outer breast feathers of Great Blue Herons are patches of special down feathers. These feathers grow continuously and are never molted. When combed with the fringed, or pectinated, claw on a Great Blue Heron’s middle toe, the tips of these feathers break down into a dust the consistency of talcum powder. The heron collects some of this “powder down” and applies it to its feathers which protects them against fish slime and other oils. (BirdNote)
Sometimes referred to as a “third eyelid,” the translucent nictitating membrane visible across this juvenile Black-crowned Night Heron’s eye serves to protect it from foreign objects and to moisten the eye while at the same time allowing the bird to retain some degree of visibility. It extends from the inner corner of the eye to the outer corner, and is drawn across the eye much like a windshield wiper. The membrane is thinner and more transparent than the fleshier upper and lower eyelids and is used periodically by birds when foraging, flying, diving, feeding young, gathering nesting material, etc. In this case, the heron’s nictitating membrane was drawn across its eye seconds before it plunged beneath the surface of the water to capture a crayfish.
Birds aren’t the only animals that possess nictitating membranes – it’s relatively common in fish, amphibians, reptiles, and mammals (but they are rare in primates).
Black-crowned Night Herons employ a number of techniques for capturing a wide variety of food, from standing stock still for a considerable amount of time waiting for prey to swim by to securing prey while swimming. They feed mainly from evening until early morning. Because they are crepuscular (feeding at dawn and dusk) as well as nocturnal (as their name implies), feeding competition from other (diurnal) herons is minimized.
The diet of opportunistic Black-crowned Night Herons includes earthworms, insects, crayfish, mussels, fish, amphibians, snakes, turtles, birds, small mammals and plant material. They have been observed actively manipulating bait (bread in one case, dragonflies in another) to attract and catch fish. As can be seen in the inset photograph, they grasp, rather than stab, their prey.
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Great Blue Herons are colonial nesters – up to 500 platform nests or more may be built in dead snags and trees bordering or in swamps, ponds and woodlands. Where trees are not available, they will nest on the ground (this usually occurs only on predator-free islands).
The nests of Great Blue Herons are built of sticks, usually gathered by the males from nearby trees and shrubs as well as the ground. The male heron flies with a stick in his bill back to the nest (see photo) where the female awaits and presents her with the stick. She takes it from his beak, pokes it into the nest and eventually lines the nest with pine needles, moss, reeds, grasses and small twigs. Although nest building and repair is at its height right now, nesting material is added throughout the nesting period.
Nests are often re-used for many years, but not necessarily by the same pair of herons. While nest fidelity is not strong, Great Blue Herons do tend to show a preference for the species of tree in a colony in which they build their nest. Nesting colonies can be used for just a few years, or for as many as 70.
When you think of a heron, you usually think of a diurnal wading bird that has long legs, a long neck and a long bill. Black-crowned Night Herons don’t possess any of these familial characteristics. Stocky and relatively short-legged and short-billed, these herons typically rest during the day and start actively hunting at dusk, continuing through the night.
Prey includes fish (half their diet) plus a wide range of other creatures including leeches, earthworms, insects, crayfish, snakes, turtles, small mammals, birds and frogs. The manner in which a Black-crowned Night Heron lures and captures its prey varies. Two of its most intriguing fishing techniques include bill vibrating (opening and closing its bill rapidly in the water to attract prey) and bait fishing – using bait to attract fish.
Great Blue Herons are colonial nesters – a rookery can have hundreds (up to 500) of nests, usually in dead snags, with one, two or three nests in a single snag. Because the chicks are in the nest for roughly two months before fledging, their interactions with both parents, especially when food is delivered to the nest, has been observed and well documented.
Newly hatched chicks peck at the adult’s bill, the nest and each other. Initially the adult returns to the nest where it stands on the rim and regurgitates food into the open bills of the chicks. The chicks get quite proficient at grabbing the adult’s bill and pulling it into the nest as soon as the parent returns. As the chicks age, the adult often regurgitates onto the floor of the nest and the chicks eat it. When the nestlings are about a month old, they take food directly from their parents.
A visit to a Great Blue Heron colony at this time of year will be rewarded with a great deal of avian activity, for their nesting season has begun and renovations are going full tilt. Males usually arrive first and settle on nests (more often as not using a different nest from last year) or begin building their own. Courtship then begins.
Great Blue Heron nests are found primarily in trees, up to 60 feet or more above the ground. Where trees are not available, herons will nest on the ground (usually only on predator-free islands). Males gather sticks and other nesting materials from the ground, nearby trees and shrubs, or from unguarded and abandoned nests, and females are usually responsible for the placement of the sticks into the nest. Nests are often reused for many years. Pictured is a Great Blue Heron returning to its nest with a branch from a White Pine tree which will be used for lining the nest. Nesting material is added throughout the nesting period.
Great Blue Heron chicks spend roughly two months in their nest before fledging, during which time they are totally dependent on both of their parents for food. During the first week after their eggs have hatched, the parents return to the nest after foraging and stand on the rim while placing regurgitated food into their chicks’ open beaks. By the second week the chicks grasp the adult’s beak briefly when the parent arrives with food, and by the end of the third week the chicks are pulling the adult’s beak into the nest, which they continue to do until they fledge. Occasionally chicks reach into an adult’s open beak to get food, but most of the time the parents put the food into their offsprings’ beaks.
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How do herons, egrets, bitterns, kingfishers, loons and other fish-eating birds with spear-shaped bills capture their prey? Do they use their bill as a spear and pierce through a fish, or do they grab the fish between their mandibles? You often read about one of these birds “spearing” a fish. However, a majority of these birds, most of the time, do not spear fish, but open and shut their bills fast enough to capture a fish in them — the spear shape of their bill lends itself to the tong-like action it performs. In addition, its shape enhances the movement of the bill through the water as the bird dives (its head or body) into the water to grasp the fish between its upper and lower mandibles.
One exception to this rule is the Anhinga, which does run its bill (which is equipped with backward grooves to prevent slippage) through fish in order to capture them. After spearing a fish, an Anhinga then shakes it vigorously off its bill, tosses it in the air, and catches and swallows it headfirst. (Photo: Great Blue Heron)
The structure of a Green Heron’s foot lends itself to a life of wading at the water’s edge while foraging for food and not sinking into the sand. Three long toes pointing forward and one pointing backward create a considerable amount of surface area, and the more the surface area the less pressure that is placed on the sand. Webbing between its outer toes adds to the snowshoe effect (and also aids the heron when it dives below the surface of the water for prey and must swim back to shore).
This foot structure comes in handy when wading in shallow water, standing on emergent vegetation or perched a low-hanging branch at the water’s edge. As testimony to this, the pictured Green Heron spent an entire morning navigating from water lily pad to water lily pad foraging for fish, insects, frogs and other aquatic life.
For those New Englanders fortunate enough to live on the coast, Snowy Egrets are a welcome sight this time of year as they return from their wintering grounds to breed. Like most herons and egrets, they acquire plumes – long, wispy feathers – on their back, neck and head during the breeding season. (These plumes were highly sought after by the women’s hat trade in the late 1800’s and early 1900’s. They were valued at $32 per ounce, twice the price of gold at the time. Eventually laws were passed to protect the birds.)
Something slightly more subtle but equally as dramatic as ornate plumage highlights the appearance of these birds in the breeding season and that is a change in bill and feet coloration. Different species of herons and egrets exhibit different color changes. Snowy Egrets’ greenish-yellow feet turn a much richer orange-yellow hue during the breeding season, and the patch of bare skin at the base of their bill (lore) changes from a yellowish color to a pinkish/reddish color, only seen at this time of year.
The low water level of most small ponds and streams this fall has at least one silver lining, and that is that consumers of fish and other aquatic creatures expend far less energy finding prey, for it is all concentrated in much smaller bodies of water. The few puddles of water in small streams contain a vast amount of life, as do small ponds.
The Great Blue Heron has the advantage of having a varied diet that is found in a variety of habitats, so it forages in grasslands, marshes, intertidal beaches, riverbanks and ponds. While amphibians, invertebrates, reptiles, mammals, and birds are all known to have been eaten by Great Blue Herons, fish are their mainstay. They often forage in ponds, where they typically wade or stand in wait of prey in shallow water, which has not been in short supply this summer and fall. While the low water level is wreaking havoc with beavers and muskrats, it provides bountiful fuel for herons, egrets, kingfishers and other birds that forage in small ponds and streams as they wend their way southward.
Green Herons (Butorides virescens) are small, crested, wading birds that inhabit wetland thickets throughout most of North America. After breeding, most tend to wander to more favorable foraging areas before migrating south to Florida, Central and South America. Migration begins in late August/early September and by mid-October, most Green Herons have departed.
Green Herons are among the few species of birds that use tools in order to lure fish to within their striking distance. Bread, mayflies, twigs, leaves, berries, earthworms and feathers are among the lures they have been observed dropping into the water as bait. To watch a video of a persistent and successful Green Heron fishing with a lure, go to https://www.youtube.com/watch?v=Porp5v5lLKk .
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Green herons are typically solitary and secretive birds, but if you find one, you often have an extended period of time to observe it, as they often slowly stalk their prey, or pose statue-like, sometimes for minutes at a time, while waiting to strike at a fish, frog or invertebrate. Three characteristics tell you that the green heron in this photograph is a juvenile: the few tufts of down that remain on its head, its streaked neck (adults have solid rufous necks) and its yellow legs (adults have orange legs).
After fledging when about three weeks old, they can soon fly. The juvenile fledglings continue to be fed by the adults for a period of time and are taught how to forage for fish. Green herons are one of very few bird species that are known to occasionally use a tool (insects, earthworms, twigs, feathers) to catch their food – they simply drop the lure and wait for small fish to appear. (A wonderful video of a green heron successfully using bread for this purpose can be seen at https://www.youtube.com/watch?v=Porp5v5lLKk.)
Great Blue Herons have returned to their nesting colonies in the Northeast and their breeding season is underway. These birds are monogamous for the duration of any given breeding season. A study found that most Great Blue Herons choose a new mate every year. After elaborate courtship displays have taken place, the pair copulates, frequently on the nest, and usually in the early morning or evening, as the female is away from the nest mid-day.
Great Blue Herons swallow their prey whole, which means they consume not only flesh, but also bones and fur (if they eat a mouse or a vole). They are able to digest almost all of the prey that they eat due to acidic stomach secretions that are capable of softening even bones. However, they are not able to digest hair, or fur. This indigestible matter is formed into pellets which Great Blue Herons regurgitate – much like owls and many other birds.
If you’ve watched a heron, egret or bittern for any amount of time, you know they strike suddenly and rapidly at their prey . They can do this because of the structure of their neck bones. According to David Sibley, modification of the sixth cervical vertebra lets them draw their neck into an “S” shape and then shoot their head and bill forward with lightning speed. This adaptation also allows these birds to fold their neck while flying, which improves the aerodynamics of their flight. (Photograph is of a Great Blue Heron.)
Numerous displays lead up to the mating of great blue herons – neck stretching, bill clacking, wing preening, circling flights, twig shaking, crest raising, neck fluffing, to name but a few. After this elaborate courtship comes copulation, which is not nearly as showy. Copulation typically takes place on the nest. The male places one foot gently in the center of the female’s back. The female leans forward, bends her ankles and holds her wings slightly away from her sides while the male lowers himself, often flapping his wings. Once the job is done, the male flies off. If you look closely you can perhaps make out that the male is grasping the female’s head/neck while copulation takes place.
Birds have a number of ways of keeping cool, which is a good thing, given the number of hot days we’ve experienced this summer, and probably for summers to come. They don’t sweat, nor do they pant, but birds do have several behavioral adaptations which reduce their temperature. Often, while exposed to the relentless heat of the sun, Great Blue Heron nestlings resort to what is called gular fluttering. They open their mouths and “flutter” their neck muscles, promoting heat loss – an avian version of panting. An even easier behavior to observe is the position Great Blue Herons will often assume on a hot day. They droop their wings (see photograph) while standing, which allows air to circulate across their body and sweep away the excess heat.
Although Great Blue Herons are colonial nesters, they forage by themselves, usually by slowly wading or standing in wait of prey in shallow water. Fish are the mainstay of their diet, but they also consume amphibians, invertebrates, reptiles, mammals, and birds. When prey is located (by sight), the heron rapidly thrusts its neck forward and grabs it with its beak. If it is small, it is sometimes tossed in the air before it is swallowed, as the photograph depicts. Most prey are swallowed whole.
Green herons are typically solitary and secretive birds, but if you find one, you often have an extended period of time to observe it, as they often slowly stalk their prey, or pose statue-like, sometimes for minutes at a time, while waiting to strike at a fish, frog or invertebrate. Three characteristics tell you that the green heron in the photograph is a juvenile: the tufts of down that remain on its head, its streaked neck (adults have solid rufous necks) and its yellow legs (adults have orange legs).