The Least Bittern is North America’s smallest heron, measuring just 28–36 cm in length and weighing about 90 grams. In Arizona, it is primarily found along the lower Colorado River valley, from Yuma to Topock Marsh, and in large marshes associated with national wildlife refuges. It also occurs in the wetlands of the lower Gila and Salt Rivers in Maricopa County and in isolated marshes such as Picacho Reservoir, Tavasci Marsh, and Patagonia Lake. Breeding has been confirmed in several counties including Pinal, Graham, Santa Cruz, and Yavapai, with nesting particularly well documented at Goree’s Pond near Coolidge.
The Least Bittern is a year-round resident in the lower river valleys, but in other parts of the state it appears mostly during spring and summer breeding seasons. It is listed as a Species of Greatest Conservation Need in Arizona and is also recognized nationally as a bird of conservation concern.
These birds rely on dense, tall stands of emergent vegetation such as cattails and bulrush, ideally mixed with open water at depths of about 1.5 to 2.5 feet. They favor wetlands larger than 11 acres or clusters of smaller marshes with a rich mix of water and vegetation. Nests are built 6 to 30 inches above water in bent-over vegetation near the water’s edge. At small sites like Goree’s Pond, successful nesting has been observed in bulrush. Clutch sizes average four to five eggs, and young fledge about 25 to 30 days after hatching.
Least Bitterns are masters of stealth. They move through reeds with agility, freeze with their bills pointed upward when alarmed, and are rarely seen in the open. Their small size and long toes allow them to climb and cling to stalks of vegetation. They feed on a variety of small aquatic animals, including fish, amphibians, insects, crustaceans, and occasionally small birds or mammals. Their calls, often the only indication of their presence, include a harsh, repetitive "kek-kek-kek" sound.
