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The heron family is a bit of a hodge-podge. The flamingoes, storks, ibises, Hammerkop, Boat-billed Heron, and Shoebill are often included but sometimes separated out into their own group(s). Genetic similarities will aid in the development of a taxonomy based on heritage. Historically tall, long-legged birds that generally hang around wetlands have been lumped in a larger “heron” group – but that is changing. Consensus says that there are four heron groups that are similar enough to be grouped almost together – but not really together: there are (day) herons (34 species), night-herons (9), tiger-herons (5), and the bitterns (13). Egrets are just medium-sized herons, that in the US, often have predominantly white plumage. On a world-wide basis the medium-sized herons (egrets) range from totally black to totally white.
Most taxonomic lists show at least 60 herons world-wide. eBird, the large data base for bird records, shows a total of 75 birds in the four heron groups. The International Ornithological Congress (IOC) says there are 72 species. So 60 to 75 it is. Some species have appeared on islands and have moved from one continent to another – whether these have become new and separate species leads to differing opinions and differing lists.
The herons will nest in colonies or separately depending on the species. Males establish a territory and display to attract and gain females and probably to repel competing males as well. The males will develop a breeding plumage that features plumes or long showy feathers. Some herons will have a single rather thick plume like a pony-tail, others will develop long loose feathers like sun-dried hair and a third group will develop aigrettes or loose flowing feathers that can be on the head, neck, or body depending on the species. It was these feathers that drove the slaughter of birds during the breeding season toward the end of the 1800s and early 1900s. This feather trade killed millions of birds – so many that feathers were often sold by the ton!
The various Night-Heron species are often geographically widespread and this results in a range of populations; perhaps some of these populations represent different species. For instance there are five subspecies of the Boat-billed Heron, four of the Black-crowned, five of the Yellow-crowned, and four of the Nankeen. Birds like this, that are strong fliers and that establish widely over the planet, are often genetically dissimilar to the original population. The longer the separation the greater the differences. Genetics will probably allow for more population/species/types of Night-Herons in the future.