Ardeidae Herons, Egrets, and Bitterns
Version: 1.0 — Published March 4, 2020
Introduction
Lithe wetland predators, herons are adapted to throwing their dagger-like skull at prey with lightning quickness and fatal accuracy. Whether standing and with great patience (even under shade that they produce with an umbrella made by their wings), or stirring up the bottom to see what they can dislodge (or attract) with their toes, these birds mix stillness with quick and decisive action. The same sharp bill that makes these birds such effective predators makes them dangerous in the hand: if you get this close, wear safety glasses. Still, they must resort to sheltered or remote nest sites to find safety from mammalian predators, and it is a strange sight indeed to see a tall heron perched on a tree-top limb, attending its large stick nest.
Habitat
Most herons live on or near bodies of water, in habitats ranging from open marsh and shores to savanna and dense forests. In general, the larger species prefer more open habitats. During the breeding season, most herons and egrets need trees or shrubs, or isolated islands, for nesting, whereas bitterns hide their nests deep in marshes.
Diet and Foraging
Ardeids have a varied diet that includes a large proportion of aquatic and terrestrial vertebrates (fish, amphibians, small birds, and mammals) and invertebrates. They vary from active, probing pursuers of prey to unflappable sit-and-wait predators. Some species have taken this foraging strategy to an extreme, luring in fish prey with shade from outspread wings or small bits of food as bait. The Cattle Egret Bubulcus ibis, on the other hand, hunts in open grasslands, where it forages close to large mammals that flush prey. All species seize their prey with a lightning quick jab and grasp of the bill.
Breeding
Herons are generally monogamous with biparental care, though some cases of polygyny and promiscuity have been reported. Most species nest in colonies, but most bitterns and some of the larger herons tend to nest solitarily. During the breeding season, many herons and egrets acquire ornate plumes on their heads and backs, as well as brightly colored bare skin. Most herons build their rough platform nests of sticks in a tree or larger shrub near or over the water, whereas bitterns build their nests of reeds in a marsh. Herons generally lay 3 to 7 eggs in a clutch. Both parents take part in nest construction, incubation, and provisioning of the young. Incubation takes 14 to 30 days (longer in larger species), and chicks hatch asynchronously, leading to sibling competition that can result in the death of the weaker chick. Chicks leave the nest after 25 to 90 days, but many are not independent of their parents for at least a couple of weeks post-fledging.
Conservation Status
Populations of 12 heron species (19%) are declining as a result of destruction and fragmentation of habitat, in addition to hunting (3 NT, 3 VU, 5 EN, 1 CR). The critically endangered White-bellied Heron Ardea insignis has a maximum estimated population of only 250 individuals.
Systematics History
Ardeidae belongs in Pelecaniformes, within which it appears to be sister to Threskiornithidae (van Tuinen et al. 2001, Ericson et al. 2006a, Hackett et al. 2008); these two together form a clade that is sister to the other members of Pelecaniformes. Alternatively, Ardeidae may be sister to Pelecanidae (Jarvis et al. 2014). Within Ardeidae, there appear to be four main clades. The first clade is composed of Tigrisoma and Tigriornis tiger-herons, the second the Boat-billed Heron Cochlearius coch learius, and the third made up of bitterns and the Zigzag Heron Zebrilus undulatus. This third clade appears to be sister to the fourth, made up of all the typical herons and night-herons (McCracken & Sheldon 1998).
Conservation Status
Least Concern |
67.6%
|
---|---|
Near Threatened |
4.2%
|
Vulnerable |
5.6%
|
Endangered |
4.2%
|
Critically Endangered |
1.4%
|
Extinct in the Wild |
0%
|
Extinct |
7%
|
Not Evaluated |
0%
|
Data Deficient |
0%
|
Unknown |
9.9%
|
Data provided by IUCN (2023) Red List. More information