The Great Blue Heron (Ardea herodias)
by Ross Vennesland
Description
The Great Blue Heron (Ardea herodias) is the largest wading bird in North America (Vennesland and Butler 2011) and a highly recognizable species in British Columbia. This majestic bird is mostly a slate grey colour, with adults having accents of blue on the flight feathers and chestnut on the shoulders. It has a mostly white head with blue stripes, creating a crown of white. Adding to its elegance, long feather plumes flow down the breast and off the back of the head of adult birds. Juveniles generally lack the colour accents of adults, being a drabber grey colour with no plumes and no white crown.
Biology
The Great Blue Heron appears somewhat ungainly in the air, using deep and slow wing beats with its long legs trailing behind its body. But while hunting, it shows great aptitude as it slides smoothly through shallow water or grassy meadows and strikes adeptly at unsuspecting prey. The eyes of the Great Blue Heron are oriented forward and downward, providing binocular vision for hunting prey below. The Great Blue Heron’s main prey is fish, for which it can be found foraging along the shores of lakes, rivers, wetlands and the ocean (Vennesland and Butler 2011). In some unusual behaviour that occasionally occurs in B.C., herons can also be found foraging from floating kelp beds, wharves and fish ponds (Vennesland and Butler 2011). It also frequently hunts in upland areas where it stalks small mammals, amphibians and any other small creatures it can snare in its long bill (Vennesland and Butler 2011). Great Blue Herons are territorial on the foraging grounds, using a wide array of sometime spectacular displays to defend their foraging sites (Vennesland and Butler 2011).
Nesting Colonies
During the breeding season the Great Blue Heron typically nests in colonies up to about 400 nests, and less frequently as solitary pairs (Vennesland and Butler 2011). Individual nests are defended, and elaborate and beautiful breeding displays are used when in colonies, including flying with the neck outstretched and the fluffing up of feathers and plumes on arrival at the nest. Males and females can be seen crossing bills when they meet upon the nest, perhaps as a greeting or sign of affection. Nests are made of sticks and are normally placed in tall trees, both coniferous and deciduous, though in areas where woodlands are scarce (e.g., the farmland dominated community of Delta, BC) they will sometimes nest in shrubs or hedgerows (Vennesland and Butler 2011). Nests are reused each year, but because they are relatively small nests, they generally require repair at the beginning of the nesting season (Vennesland and Butler 2011). The males collect sticks from nearby areas and the females construct and repair the nest (Vennesland and Butler 2011). Incubation is shared between males and females. We have very limited data on how individual herons behave because they are difficult to trap and mark individually, but the results of one study (Simpsone et al. 1987) suggest that there is considerable interchange between colonies between years and few herons mate with the same individual between years (seven of 21 individuals marked in 1979 did not return to the same colony in 1979; zero of 5 banded pairs in 1978 were paired in 1979).
Taxonomy
There are two subspecies of Great Blue Heron recognized in British Columbia, A. h. herodias, the most widespread subspecies in North America, which occupies the centre and east of southern British Columbia, and A. h. fannini, which occurs along the coast west of the Pacific Coast ranges (Vennesland and Butler 2011). A. h. herodias is generally migratory, flying south in the winter as far south as central America, though some birds will winter in more northern areas where water remains ice free (e.g., Okanagan Valley). On the coast of BC, A. h. fannini is considered to be non-migratory. The moderated climate of the coast enables Great Blue herons to persist through the winter, and this behaviour coupled with the barrier presented by the Pacific Coast Range that is hypothesized to have resulted in the smaller size and darker plumage of the fannini subspecies.
Research
Key studies across various topics include the following. Vennesland and Butler (2011) provides the most recent and most comprehensive life history review for the Great Blue Heron in North America. Butler (1997) reviewed of breeding behavior, reproductive success, foraging behavior, and the energetics of growth and reproduction of herons in British Columbia. Foraging ecology and behavior has been reviewed and studied by Kushlan (1976, 1978), Gawlik (2002) and Kelly et al. (2003), and specific to British Columbia by Butler (1995). Contaminant effects on reproduction have been documented by Champoux et al. (2006), and specific to British Columbia by Harris et al. (2003) and Elliott et al. (2005). Human and predator disturbance has been reviewed by Parnell et al. (1988), and specific to British Columbia studied and reviewed by Vennesland and Butler (2004) and Vennesland (2010).
