Yellow-crowned night heron

Distribution

The Yellow-crowned Night-Heron is found exclusively in the Americas, and its distribution depends closely on food availability.

Status

The Yellow-crowned Night-Heron is generally not considered a threatened species, as the population size is very large, its range is wide and it has a stable trend.

Habitat

The Yellow-crowned Night-Heron looks for shallow water to live in: marshes, wooded swamps, and lakeshores for inland populations, and thickets, mangroves and cliff-bound coasts for coastal populations. It can also be found in areas that don’t always have enough water, but that get flooded on a regular basis. Its habitat is closely linked to that of the crustaceans that make for most of its diet, and it tolerates fresh water, brackish water and saltwater.

Another important habitat factor is nesting sites. The Yellow-crowned Night-Heron needs bushes or trees to build nests, although it will use rock ledges where vegetation is unavailable.

Unlike the Black-crowned Night-Heron, the Yellow-crowned does not mind living near humans and can be found in wooded neighborhoods, nesting on rooftops and driveways. Such cohabitation may not go smoothly and can create conflicts with humans.

Reproduction

The Yellow-crowned Night-Heron typically has one brood per year. It will try and replace a brood completely lost if it is not too late into the breeding season, but not a partially lost brood. The female lays two to six eggs, depending on the conditions, especially the temperature. The eggs are oval and smooth, with a pale green-blue color. Both parents start guarding the nest as soon as the first egg is laid, and they both incubate the clutch in turn.

24–29 days later, the young hatch, vulnerable and entirely dependent on their parents. They look nothing like the adults with their white-grey short, soft feathers, their wide blue eye-ring and their yellow bill.

During the first two weeks, both adults brood the young. After this period, they will only shelter the chicks from sun, rain or strong wind. Both parents feed the young, taking turns gathering food and guarding the nest. They regurgitate food in the center of the nest rather than feeding each chick individually. The young do not recognize their own parents and will adopt their begging-for-food behavior whenever any adult is around them; the adults, on the other hand, recognize their own chicks and are aggressive towards other offspring, driving them away and refusing to feed them.

When the nest grows too tight for the chicks, they start venturing to its edges; they leave the nest 36–42 days after hatching. They cannot fly yet, so they walk around the nests and return daily to the colony to be fed, and they keep doing so for another three weeks. They start taking short flights by the sixth week, and are capable of sustained flight between their seventh and eleventh week. Once again, crab availability intervenes at this point: the more crab are available to the young, the less often they come back to the roost and the less they rely on adults to be fed.

The immature birds will roost with the adults until the end of the breeding season, after which they disperse to unknown destinations. They will not be seen on the breeding grounds until they have acquired their adult plumage, and little is known about their ecology during this time. This mystery is actually a research priority about the Yellow-crowned Night-Heron.

Food

The Yellow-crowned Night-Heron eats mainly crustaceans as well as insects, some fish or worms. It can also feed on lizards, small rodents and small birds. The geographic location of the heron is closely related to the prey it may find, and the size and shape of its bill allows it to hunt for prey of specific size.

The Yellow-crowned Night-Heron may forage any time of the day and night, although it prefers the night to feed the young. It becomes very aggressive if another individual approaches when foraging, but will tolerate a safe distance of about ten meters. It selects prey visually, either stalking it or standing and waiting for it to come within reach. When hunting crayfish, the heron stands at the entrance of the burrow, always facing the sun so its shadow is not cast over the entrance of the burrow, which would alert the crawfish. It can also chose an alternate pattern of walking slowly towards prey with its body bent and its head retracted, then standing and waiting before walking slowly again, sneaking up effectively on unsuspecting crabs. Sometimes it can be seen running in shallow water after a prey, but it will not follow one in deep water.

Once close enough, it lunges with its bill and, if it is a small prey, it swallows it whole. If it is a larger prey, the heron will try to dismember it in order to eat the body first and the legs last, or to jab it straight through the body. It will also carry crabs, molluscs or fish away from the water to prevent them from escaping.

Any indigestible material, such as crab shells, is ejected in a pellet, and it is quite common to find shells and pellets scattered around foraging and nesting areas.

Predators

Being a highly specialized crustacean feeder, the Yellow-crowned Night-Heron has no real competition for food. The adults have virtually no predators, but the nests are vulnerable to other animals. Both the eggs and the young are an appealing meal to American Crows and some mammals such as raccoons. Crows are also known to harass adult Yellow-crowned Night-Heron out of their nest, or displace the eggs in order to use the nest themselves. The importance of the impact of such predation varies geographically, Virginia being the state where it matters the most.