Great Blue Heron an indicator of wildlife sustainability in the Georgia Basin

What is Happening?

Evidence based on the Canadian Wildlife Service’s Breeding Bird Surveys (BBS) conducted between 1969 and 2000 indicates that the Great Blue Herons of the coast of British Columbia (includes Queen Charlotte Islands and Vancouver Island) are declining at a rate of 9.4 per cent per year. However, the decline is not statistically significant and the available data set is very small and does not meet the minimum requirements for analysis of the Breeding Bird Survey. Therefore, the decline should be viewed with caution. Observations indicate that few herons now breed on the Sunshine Coast although they were numerous in the 1980’s. Although not as dramatically as the Sunshine Coast, the numbers on Central Vancouver Island have also dropped in recent years. A 1998-99 study of 35 of these breeding colonies reported that their breeding productivity is the lowest in North America and has declined since 1971 (Vennesland 2000).

Source: Downes, 2002. Environment Canada, Canadian Wildlife Service, Ottawa, Ontario. Note: the annual index is the estimated average number of birds that would be seen per BBS route per year if all routes in the area of analysis were conducted in any one year. Standard BBS analyses require a minimum sample size of 15 routes. In this case only 13 routes were available therefore results should be viewed with caution. The trend (-9.4%) is the average annual percent change between 1969 and 2000 and is not statistically significant.

GRAPH DATA

The Great Blue Heron, the largest heron of North America, is widely distributed in Canada but the estimated 1500 pairs of coastal British Columbia Great Blue Heron are distinct from herons elsewhere in Canada. The coastal birds are non-migratory and remain isolated year round from heron populations that migrate. This isolation has led to adaptations with among other features a darker plumage and subspecies classification, Ardea herodias fannini. 

Distribution of Great Blue Heron colonies in the Georgia Basin 1998 and 1999 (from Vennesland, 2000).

The majority of these herons, about four-fifths of them, nest in five large colonies each with well over 100 breeding pairs. They include the Point Roberts, University of British Columbia, Chilliwack, Mary Hill, Alouette Lake and Salt Spring colonies. The large colonies have existed for many years and even decades, although heron colonies are not static and may shift location from time to time. The remaining BC coastal herons nest in small colonies or as solitary pairs and typically relocate their nesting sites every few years. The number of herons nesting in colonies is positively related to the area of eelgrass on nearby beaches. Large beaches at the mouth of the Fraser River estuary support hundreds of pairs of herons, whereas the smaller areas of eelgrass on Vancouver Island beaches support only a few hundred herons in total.

There is good evidence that the timing of the breeding season of the Great Blue Herons is also related to the abundance of food at nearby feeding areas. In the spring, the duration of low day time tides increases and the warming rays of the sun triggers the growth of eelgrass on shallow beaches. The eelgrass habitat attracts small fish to feed and reproduce and they in turn attract the herons. The plentiful food is used for egg production and the laying of eggs by herons is closely timed with this seasonal ebb and flow of tides.

Why is it Happening?

Environment Canada is trying to understand why the number of coastal Great Blue Herons does not appear to be decreasing given the high nesting failure. The most likely cause of abandonment is nearby human and eagle activity. The habitat requirements for nesting herons are fairly specific. They require a mature woodlot as they usually nest 15 meters above ground and it needs to be located within 3 kilometers of foraging sites. Some herons will abandon their colonies as a result of nearby human activity and from depredations of eggs, chicks and adult herons by eagles.

Eight out of ten herons on the coast live around the Strait of Georgia. This is also where two thirds of BC’s human population and three quarters of its labour force lives. Some herons are very susceptible to human disturbance during the nesting period and this can have a negative effect on nesting success. In the lower Fraser River Valley between 1981 and 1986 for every 1,000 increase in human population 28 hectares (ha) of rural land were converted into urban use (Moore,1990). This population growth impacted on heron habitat and further impacts are expected given the Georgia Basin population is projected to about double in the next 20 years. Herons are also affected by the food they eat. Contaminants now found in their tissues can be traced to growth in agriculture, manufacturing and forest industries, and urban developments.

Herons are also susceptible to disturbance from Bald Eagles that prey on chicks and adults in the colonies. A nesting heron study conducted in 1999 in the Georgia Basin concluded that Bald Eagles targeting heron eggs or young were responsible for the abandonment of 13 of 31 colonies (Vennesland, 2000). However, humans might have been ultimately responsible by creating a fragmented landscape that allowed eagles easy access to herons and their nests. Bald Eagle numbers on the south coast of British Columbia have gone up significantly. Scientists speculate the increase might be a delayed response to the banning of certain chemicals such as DDT that previously had affected their breeding success.

Why is it Significant?

The specific habitat requirements for herons and their susceptibility to human disturbance poses an increasing threat to this species in BC and particularly in the populous Georgia Basin. In 1988, the Canadian Nature Federation designated the 120 nest McFadden Creek Heronry on Salt Spring Island a Globally Important Bird Area. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) has given this coastal heron subspecies the status of "special concern". Similarly, the British Columbia Ministry of Sustainable Resource Management, has placed this subspecies on their blue-list as it is considered to be both vulnerable and at risk.

What is Being Done?

Environment Canada’s Canadian Wildlife Service has formed a partnership with the British Columbia Ministry of Water, Land and Air Protection, and the WBT Wild Bird Trust of British Columbia to establish the Heron Stewardship Program. The objective of this program is to reduce the impact of humans at nesting colonies and important heron feeding areas. The Heron Stewardship Program worked with the Waterbird Watch Collective, WBT Wild Bird Trust of BC and Islands Trust Fund on Salt Spring Island to purchase and manage 5.07 ha (12.5 acres) of land supporting one of the largest heron colonies (125 nests) in BC, the McFadden Creek Heronry. The herons abandoned McFadden Creek in 2001 but over 100 pairs returned to nest in the spring of 2002. Agreements to manage lands for herons are also in place or in the works at four other colonies in the region. One of those lands, the Chilliwack Great Blue Heron Nature Reserve was officially opened on May 15, 2002. The City of Chilliwack working with the Rotary Club, First Nations, provincial and federal governments, and environmental organizations, established the Reserve on the shore of the Vedder River near Chilliwack. The Reserve includes 132 hectares of lowland forest where about 100 pairs of herons have nested for decades. The Rotary Club committed $300, 000 to the construction of an interpretive centre on the site and the City of Chilliwack built trails in the nearby forest. The centre is open to the public at the south end of South Sumas Road.

In 2001, the Heron Stewardship Program in BC expanded to include government and non-government groups and individuals in Washington State into the Heron Woking Group. The Working Group collaborates on designing research and census protocols, conservation advice, seeking funding support and providing a web site forum for information.

Canadian Wildlife Service scientists are working with students from the Centre for Wildlife Ecology at Simon Fraser University to understand the response of herons to eagle predators at their nests and the food supplies. The scientists are examining if small groups of herons are establishing new colonies in response to heightened predation by eagles at large colonies.

For more information contact: Rob.Butler@ec.gc.ca

Check the following sites for additional information on this indicator:

• Hinterland's Who's Who
• Canadian Bird Trends Database for Great Blue Heron
• Species at Risk - Great Blue Heron fannini subspecies
• What you can do for wildlife
• Environment Canada's Millennium Eco-Communities

The following Web sites are not under the control of Environment Canada (EC) and they are provided solely for the convenience of users. Environment Canada is not responsible for the accuracy, currency or the reliability of the content. Environment Canada does not offer any guarantee in that regard and is not responsible for the information found through these links, nor does it endorse the sites and their content. Users should be aware that information offered by non Government of Canada sites that are not subject to the Official Languages Act, and to which Environment Canada links, may be available only in the language(s) used by the sites in question.

• Canadian Important Bird Areas Program
• The Great Blue Heron Book
• See Webcam of the heron colony in Beacon Hill Park, BC
• Washington Department of Fish and Wildlife HERONcam

For references used in this indicator click here.