<Li> <P> Flying heron </P> </Li> <P> This species usually breeds in colonies, in trees close to lakes or other wetlands . Adults generally return to the colony site after winter from December (in warmer climes such as California and Florida) to March (in cooler areas such as Canada). Usually, colonies include only great blue herons, though sometimes they nest alongside other species of herons . These groups are called a heronry (a more specific term than "rookery"). The size of these colonies may be large, ranging between five and 500 nests per colony, with an average around 160 nests per colony . A heronry is usually relatively close, usually within 4 to 5 km (2.5 to 3.1 mi), to ideal feeding spots . Heronry sites are usually difficult to reach on foot (e.g., islands, trees in swamps, high branches, etc .) to protect from potential mammalian predators . Trees of any type are used when available . When not, herons may nest on the ground, sagebrush, cacti, channel markers, artificial platforms, beaver mounds, and duck blinds . Other waterbirds (especially smaller herons) and, occasionally, even fish and mammal - eating raptors may nest amongst colonies . </P> <P> Although nests are often reused for many years and herons are socially monogamous within a single breeding season, individuals usually choose new mates each year . Males arrive at colonies first and settle on nests, where they court females; most males choose a different nest each year . Great blue herons build a bulky stick nest . Nests are usually around 50 cm (20 in) across when first constructed, but can grow to more than 120 cm (47 in) in width and 90 cm (35 in) deep with repeated use and additional construction . If the nest is abandoned or destroyed, the female may lay a replacement clutch . Reproduction is negatively affected by human disturbance, particularly during the beginning of nesting . Repeated human intrusion into nesting areas often results in nest failure, with abandonment of eggs or chicks . However, Vancouver B.C. Canada's Stanley Park has had a healthy colony for some years right near its main entrance and tennis courts adjacent to English Bay and not far from Lost Lagoon . The park's colony has had as many as 183 nests . </P> <P> The female lays three to six pale blue eggs . Eggs can measure from 50.7 to 76.5 mm (2.00 to 3.01 in) in length and 29 to 50.5 mm (1.14 to 1.99 in) in width, though the smallest eggs in the above sample may have been consider "runt eggs" too small to produce viable young . Egg weight ranges from 61 to 80 g (2.2 to 2.8 oz). One brood is raised each year . First broods are laid generally from March to April . Eggs are usually laid at two - day intervals, incubated around 27 days, and hatch asynchronously over a period of several days . Males incubate for about 10.5 hours of each day, while females usually incubate for the remainder of each day and the night, with eggs left without incubation for about 6 minutes of each hour . </P>

Where do great blue herons build their nests
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