Montana Field Guide

Largest heron in North America, 60 cm tall, 97 - 135 cm long, 2.1 to 2.5 kg mass. Wings long and rounded, bill long and tapered, tail short. Upperparts gray, fore-neck streaked with white, black and rust-brown. Bill yellowish. Legs brownish or greenish. In flight, folds neck in "S" shape and extends legs along the body axis; deep slow wingbeats. (Butler, Robert W. The Birds of North America, No. 25, 1992).

Bozeman area migration periods are March 25 to April 15 and July to October 1, with a fall peak of August 15 (Skaar 1969).

Great Blue Herons in northwestern Montana nested primarily in cottonwoods in riparian zones, and also in drier, coniferous sites. Nesting trees are the largest available. Active colonies are farther from rivers than inactive colonies. The number of nests in the colony corresponded to the
distance from roads (Parker 1980).

Feeds mostly in slow moving or calm freshwater. (Butler 1992) Eats mostly fish but also amphibians, invertebrates, reptiles, mammals, and birds. (Palmer 1962, Kushlan 1978, Verbeek and Butler 1989).

Mostly monogamous. Birds choose new mates each year. (Simpson 1984). Nests mostly in trees up to 30 m or more above the ground. Where trees are not available, nests on the ground. Clutch size is 2 to 6 eggs. (Butler 1992). Rookery activity has been seen as early as March 23 (Skaar 1969). Reproductive success was not affected by the number of breeding birds in the colony (Parker 1980). Breeding begins in April, and young may still be in the nest in July.