The great blue heron, seen in two photographs representative of the bird's home in the northern hemisphere winter and summer. Left: A mangrove swamp at Playa Costa Verde, Holguin province, northeastern Cuba, 20 January 2014. Right: Sunset view of another (hey, it could be the same!) individual on Trout Creek, 200 metres west of the confluence with the river Trent in Campbellford, 08 July 2014.

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The earliest and latest sightings of this unmistakable bird over the 25-year span in 1998-2023 were 25 March and 19 November. 90 percent of sightings are over the six months from May through October. This large heron is often seen in a powerful launch, great wings flapping, when he or she is disturbed during hunting along a shallow creek. At other times it may be seen motionless, reed-like, waiting for a meal at the vegetated margin of a body of water. This heron is occasionally seen flying overhead with powerful, unhurried wing beats, but is most reliably found along the watercourses. These include the Trent river itself, including the gorge on the west flank of Ferris Park and the Percy Reach downstream, and along the walk between locks 8 and 9 of the waterway. One to three herons would be a normal sighting day, but a rookery with a dozen of these birds was noted near lock 8 in May 2000. An early sighting of a pair was made on 28 March 2023, in a tree with 5 big untidy nests, which the birds seemed to be inspecting. The location was west of the canal a few hundred metres south of lock 9, so in the same area as the observation in 2000. The Crowe Bridge Conservation Area is frequented by this species, as are some of the smaller tributaries, such as Trout Creek. The most consistently elevated numbers of sightings were in 2002-2007, and without further analysis of the data the explanation is not obvious. One possibility is reduced numbers of sightings along Trout Creek in subsequent years: this could be due to a change in the observers' walking habits, rather than a drop in actual numbers of birds. Walking along the creek will sometimes flush a bird wading in the shallow water, upstream or beside the outer streets of the town.

This bird is a common migrant and summer resident from late March to late November at Presqu'ile provincial park, roughly 40 km to the south, with extreme sightings on 11 March (1989) and 02 January (1977). They have wintered successfully in the Brighton area, but potential feeding sites generally freeze in the area of the Presqu'ile peninsula (LaForest, 1993, pp.43-44). In Peterborough county, to the northwest, the great blue heron has mostly been noted from 04 March to 02 October (Sadler, 1983, pp.38,168). Most are gone by early October, but a few have tried to overwinter, and been seen in late November, with one remarkable sighting on the Otonabee River on 14 January 1977.

The great blue heron is virtually ubiquitous in its occurrence across southern Ontario, especially along the southern margin of the Canadian shield, with its abundant lakes and sporadic woodlands (Cadman et al., 1987, pp.50-51). A pair may build a single nest, but more than 99% of great blue heron nests in Ontario are in treetop colonies, which average about 35 nests and typically have a lifespan of about 10 years, and sometimes longer (Cadman et al., 2007, pp.158-159).

References

Cadman,MD, Eagles,PFJ and Helleiner,FM (1987) Atlas of the Breeding Birds of Ontario. Federation of Ontario Naturalists and Long Point Bird Observatory, published by University of Waterloo Press, 617pp.

Cadman,MD, Sutherland,DA, Beck,GG, Lepage,D and Couturier,AR (editors) (2007) Atlas of the Breeding Birds of Ontario, 2001-2005. Bird Studies Canada, Environment Canada, Ontario Field Ornithologists, Ontario Ministry of Natural Resources, and Ontario Nature, 706pp.

LaForest,SM (1993) Birds of Presqu'ile Provincial Park. Friends of Presqu'ile Park / Ontario Ministry of Natural Resources, 436pp.

Sadler,D (1983) Our Heritage of Birds: Peterborough County in the Kawarthas. Peterborough Field Naturalists / Orchid Press, Peterborough, ON, 192pp.