Photo of a yellow-crowned night heron wading on the shore.  Photo credit to Kenneth G. Ransom.Yellow-crowned night herons are waterbirds, so they occupy wetlands, costal regions, and wet inland environments near lakes and rivers (Bagley and Grau 1980). Most American yellow-crowned night heron populations reside in the southeast region of the continental U.S. (United States Forest Service 2004). Even so, populations of Nyctanassa violacea have been spotted throughout different inland regions such as Wisconsin (Wyman and Wyman 1941), Kentucky (Suthard 1926), and Illinois (Bellrose 1938). These herons inhabit environments outside the United States as well; populations of the yellow-crowned night heron have been studied in Brazil (Martínez 2004) and Bermuda (Wingate 1982). Though these night herons have been found in different regions and continents, they are stenotypic birds that thrive in a limited habitat range (Martínez 2004).

Nyctanassa violacea prefer to inhabit wet, tropical, and coastal environments (Wingate 1982) so they can feed in shallow bays and shores (Watts 1988). Foraging in these environments gives the yellow-crowned night herons considerable access to crab (Martínez 2004), their main food source (Wingate 1982; Riegner 1982). Yellow-crowned night herons possess structural and behavioral adaptations for preying on crustaceans, so their habitat must be rich in crab to reflect their dietary needs and hunting styles (Rienger 1982). In fact, Nyctanassa violacea are so dependent on crustaceans, their residence areas show a strong correlation with high population levels of crab; other birds with a wide range of prey do not choose habitats in correlation to specific prey populations (Martínez 2004).

Another benefit to living near tropical bays is the ability to feed during low tide. When large areas of the bay are exposed during low tide, yellow-crowned night herons swoop in to hunt unprotected crab (Watts 1988). However, not all foraging locations of Nyctanassa violacea provide the luxury of low tide, so the heron has developed flexible hunting strategies. One technique, the “sit-and-wait” strategy allows yellow-crowned night herons to hunt without expending a lot of energy (Riegner 1983).
Because of the abundance of aquatic life, yellow-crowned night herons often have to share their habitat with other hunting waterbirds. The scarlet ibis, for example, shares a habitat with the yellow-crowned night heron in parts of South America. Unlike the night heron, the scarlet ibis is flexible in prey and will hunt on a wide range of organisms besides crab. Though the scarlet ibis and yellow-crowned night heron share an environment, these two birds probably don’t experience much competition for food (Martínez 2004).

                                                                       Figure 1.1. This map shows the concentration of yellow-crowned

                                                                                        night heron populations on the continental U.S. (USGS).

Though yellow-crowned night herons are found in a variety of different regions, they are heavily adapted to a specific wet environment. The main reason for focusing on this type of habitat is the night heron’s need for a high supply of crab. For more specifics on yellow-crown nigh heron habitats, visit the Cornell Lab of Ornitololgy.These animals have developed specific strategies and adaptations for hunting crab, and are usually able to acquire their supply with little competition.  In addition to adapting to this specific environment, the yellow-crowned night heron has evolved to posess characteristics in form and function to facilitate survival.