Great blue heron (fannini subspecies) COSEWIC assessement and update status report: chapter 7

Habitat

The habitat of the Pacific Great Blue Heron is described byButler(1995; 1997) and Gebauer and Moul (2001). This subspecies forages along the seacoast, in fresh and saltwater marshes, along rivers and in grasslands. Smaller numbers of herons forage in kelp forests, from wharves and at anthropogenic waterbodies (e.g. ornamental ponds and fish farms). Most herons nest in woodlands near large eelgrass (Zostera marina) meadows, along rivers, and in estuarine and freshwater marshes. In autumn, juvenile herons occupy grasslands on the Fraser River delta, and adults occupy estuarine marshes, riverine marshes and grasslands. All known foraging and nesting occurrences are within the Coastal Western Hemlock and Coastal Douglas Fir Biogeoclimatic Zones.

Habitat requirements

Foraging habitat

Breeding Pacific Great Blue Herons require accessible prey within about 10 km of a nesting location (Butler 1995). Important foraging habitats for Pacific Great Blue Herons include aquatic areas such as tidal mudflats, riverbanks, lakeshores and wetlands (Butler 1992; 1997; Gebauer and Moul 2001). During winter on the coast, when aquatic prey are less abundant due to a reduced duration of daytime low tides, fallow agricultural fields become important foraging areas for adult and juvenile herons (Butler 1995; 1997). Inland fields are considered an important foraging habitat for both adults and juveniles in the lower Fraser Valley and on southern Vancouver Island (Gebauer and Moul 2001). The number of herons that use non-aquatic foraging habitats is not known, but large numbers of herons reside in south-coastal areas (Gebauer and Moul 2001), so it is likely that these areas are an important foraging habitat for a significant number of herons. Some foraging habitat is not used by herons each year, suggesting that population growth might not be limited by available foraging habitat.

Nesting habitat

Pacific Great Blue Herons are mostly arboreal nesters and colonies are typically situated in forests near to (usually <10 km from) suitable foraging areas (Butler 1991; 1992; 1995; 1997). Nesting usually occurs at sites that are relatively free from disturbance by human activities, but sometimes occurs in developed areas. Large colonies require more suitable forest than small colonies. Colonies are located in both urban and rural areas, using relatively contiguous forest, fragmented forest and solitary trees (Butler 1997; Vennesland 2000).

Pacific Great Blue Heron colony locations are dynamic, especially in areas of high disturbance (Butler 1992; Vennesland 2000). Some colonies are used for many years (e.g., Shoal Island, Pacific Spirit Park and Point Roberts; all >25 years), but most colonies, especially those with fewer than 25 nests, are relocated every few years (Gebauer and Moul 2001). A site will be re-used by individual herons that failed in their first nesting attempt if other herons are present and if there is sufficient time to complete a nesting cycle (Vennesland 2000). If an entire colony abandons and there is sufficient time to complete a nesting cycle, herons will occasionally return as a group to the same or different colony site in the same year (Vennesland 2000). Herons will sometimes return to a site after one or more years of no use (Moulet al. 2001; Chatwin et al. 2006).

Habitat trends

Foraging habitat

Suitable foraging habitat likely is declining in British Columbia (Gebauer and Moul 2001), though quantitative information on habitat trends is not available. The size of Great Blue Heron populations has been correlated with the area of foraging habitat available locally (Gibbs and Kinkel 1997), and consequently the largest concentrations of Pacific Great Blue Herons occur around the large estuaries of south-coastal British Columbia, primarily the Fraser River delta where extensive mudflats and eelgrass beds provide abundant foraging locations (Butler 1995; Eissinger 1996). These habitat sites also are highly threatened because most of the province’s human population is located near these areas (Butler 1997; Gebauer and Moul 2001). For example, the magnitude of use of some foraging locations (e.g., Boundary Bay) may currently be limited by the amount of suitable nesting habitat that remains undeveloped (B. Smith, unpubl. data; see discussion of nesting habitat below).

Although native eelgrass beds are declining globally, some small and localized habitat gains have been seen on Roberts Bank on the southern Fraser River delta due to jetty construction for a ferry terminal and shipping port (Butler 1997). Outside the Georgia Basin, Pacific Great Blue Herons are scarce but widespread along the coast and feed from kelp beds, wharves and floating objects, and wade in shallow water. There is no loss of suitable habitat for these herons and some might benefit from installations of wharves and fish farms where they can access fish in deep water. At a coast-wide level, however, these potential habitat gains likely are insignificant and probably are overshadowed by habitat loss due to development on different sites, especially in the lower Fraser Valley.

Nesting habitat

Suitable tall trees as nesting habitat for Pacific Great Blue Herons near foraging areas have declined in some parts of British Columbia over the past century due to increases in the size of human populations and industry (Butler 1997, Gebauer and Moul 2001). Especially hard hit is the lower Fraser Valley (Moore 1990, Butler 1997), where the human population is projected to grow from about 2.5 million in 1990 to about 4 million in 2020 (Georgia Basin Ecosystem Initiative 2002). Habitat destruction in south coastal British Columbia has resulted in the abandonment of at least 21 colonies (measured from 1972 to 1985 and from 1998 to 1999; Forbeset al. 1985b; Gebauer 1995; Vennesland 2000; Vennesland 2006). Smith et al. (unpubl. data) used spatial analysis of the landscape around Boundary Bay to examine the availability of nesting habitat within 15 km of known important foraging locations (the distance at which the energetic cost of flight was 90% of foraging intake that could be provisioned to young). Results showed that nesting habitat is severely limited in this area. Although the foraging habitat in this location can theoretically sustain a large heron population, available nest sites likely limit the population. Perhaps demonstrating this, herons in at least three locations in this area are nesting in untraditional habitats (e.g., farm field hedgerows).

Furthermore, the quality of Pacific Great Blue Heron nesting habitat might be declining as a result of increased disturbance by humans and eagles. Although some herons are persisting in urban settings, others seem reluctant to venture close to humans. Furthermore, Vennesland and Butler (2004) reported that heron nesting productivity was negatively correlated with the level of human activity near colonies. The primary mechanism for this relationship was eagle predation of heron nests, with direct human disturbance as a secondary mechanism. Thus, the impact of eagle predation may be higher as urbanization increases. This may be compounded by the fact that eagle populations in the Strait of Georgia are thought to benefit from humans through, for example, gull populations being enhanced by human refuse (Vermeeret al. 1989).

Outside the Georgia Basin, Pacific Great Blue Herons are scattered in small groups and as individuals that nest in the forest. Few nests have been found and all were within a few kilometres of foraging sites. There is no shortage of trees for herons in these areas, so nesting habitat appears to be readily available and has not significantly declined. However, more work is required to locate heron nests in these remote regions as data are limited.

Habitat protection/ownership

Section 34 of the British Columbia Wildlife Act (1982; updated 1999) protects heron nests (and consequently also nest trees), but does not provide for buffer areas. The British Columbia Forest and Range Practices Act (2004) has guidelines to protect heron colonies (i.e, through the Identified Wildlife Management Strategy) on Crown Land, including provision of buffer areas (Vennesland 2004). However, no reserves have been established under this legislation, so currently it affords no protection. No other habitat outside of parks, Wildlife Management Areas (through the British Columbia Wildlife Act) or National Wildlife Areas (through the Canada Wildlife Act) receives legal protection.

On private land, the British Columbia government advises land users how to best protect wildlife with largely non-legal documents such as the Environmental Best Management Practices for Urban and Rural Land Development in British Columbia (or ‘Develop with Care’) series produced by the Ministry of Environment (MOE 2007). However, there is little legislation to force action on recommendations in these mostly advisory documents. Municipalities have considerable control over the land base within their jurisdiction with the capability of zoning land for different uses and identifying Development Permit Areas, among other regulatory powers. However, due to the high economic cost of wildlife conservation to landowners, implementation of conservation actions is limited and variable across jurisdictions.

Foraging habitat for Pacific Great Blue Herons includes land and waters under federal jurisdiction (e.g., tidal areas, rivers, national parks, National Wildlife Areas, etc.) and provincial jurisdiction (e.g., private lands, municipal lands, provincial parks, Wildlife Management Areas, etc.). It is not known what proportion of foraging areas are under formal protection, but some notable sites that are protected and support large numbers of foraging herons include Boundary Bay, Sturgeon Bank, Pitt Addington Marsh, Coquitlam River and Parksville-Qualicum Beach Wildlife Management Areas (provincial), and Alaksen, Qualicum and Wigeon Valley National Wildlife Areas (federal). However, regardless of their protective status, many of these sites are under threat from oil spills or other catastrophic events (e.g., Sturgeon Bank and Boundary Bay from nearby ferry and freighter traffic).

Currently active Pacific Great Blue Heron nesting colonies are located in protected and non-protected lands under the control of federal, provincial, regional and municipal governments and on private land. Table 1 lists current nesting locations on protected lands. These seven sites account for 14% of known active locations (n = 49 sites active in 2005), and afford some level of protection to the nesting sites of 37% of the documented nesting pairs in 2005 (n = 1943 nesting pairs). Nevertheless, it should be noted that heron colonies are dynamic in nature and frequently re-locate (Butler 1997; Vennesland 2000). Both Stanley Park and Deer Lake Park are at recently colonized locations, and McFadden has declined from a maximum of 138 active nests in 2000 to two in 2005 (Table 1). In addition, four of the protected sites in Table 1 (Beacon Hill, Salal Park, Stanley Park and Deer Lake Park) are located in municipal parks with high levels of human disturbance. High levels of human disturbance have been correlated with reduced nesting productivity (Vennesland and Butler 2004), so habitat quality at these locations may be low. The other three sites are either fenced or have controlled access, measures thought important to long-term site viability (Carlson and McLean 1996). Of the further 39 sites used by herons for nesting in 2005 that are not protected, four were on Indian Reserves (8%) and 35 (71%) were located on unprotected land under provincial jurisdiction (mostly private ownership). In 2006, three nests were located in Gwaii Haanas National Park (Queen Charlotte Islands). No nests are known within Pacific Rim National Park or Gulf Islands National Park, though they likely do nest there (e.g., a few pairs have been found nesting near Bamfield next to Pacific Rim National Park and large numbers of herons nested on Sidney Island in what is now the Gulf Islands National Park from 1974 to 1990).

Table 1. Pacific Great Blue Heron colonies active in 2005 that have protection in place. Included is general geographic location and number of active heron nests in 2005 (B.C. Conservation Data Centre 2007).
Col_ID Col_Name Location Colony size (no. active nests) Protective Status
H101-001 Beacon Hill Victoria 103 Municipal Park
H101-005 McFadden Creek Saltspring Island 2 Local conservation lands
H101-038 Salal Park N. Saanich 11 Municipal Park
H204-009 CFB Chilliwack Chilliwack 203 Municipal Conservation Area
H208-002 Stanley Park Vancouver 176 Municipal Park leased from the Department of National Defence
H208-005 Mary Hill Port Coquitlam 222 Provincial Wildlife Management Area
H208-044 Deer Lake Park Burnaby 4 Municipal Park

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