Wildlife : Population

Below are links to two maps that outline some of the most recent popluation numbers on record for the Vancouver Island & Lower Mainland region. The third link is a report as written by: Erica L. McClaren as prepared For: Trudy Chatwin, Ministry of Water, Land and Air Protection.

• GBHE_Report_2003_Fig2.jpg (360 KB)
• GBHE_Report2003_Fig1.jpg (444 KB)
• GBHE Report (892 KB - PDF)

Heron Colony Inventory and Monitoring

Heron colonies that were selected for monitoring in 2003 were active between 1999-2002 and a few additional colonies were selected because they were identified to be important because of land use pressures. Data on heron colony activity, nest success and productivity were collected using standardized methodologies outlined by the Resource Inventory Standards Committee (RISC; 1998), Moul et al. (2001), and Vennesland (2003a).

In March 2003, a preliminary assessment of heron colony activity was conducted through a telephone survey of volunteer contacts for 46 heron colonies (Vennesland 2003b). Between April and August, 2003 one to five site visits occurred at heron colonies. Prior to visiting heron colonies, their locations were derived from a heron database maintained by the MWLAP in Nanaimo, BC and landowner’s were contacted for permission to access colonies on private lands.

Assessing Heron Colony and Nest Activity

Heron colonies were initially visited between April and May to determine the presence of nesting herons. These visits were conducted 50-100 m from the colony to avoid disturbance which may lead to colony abandonment or egg/nestling predation (Butler 1997, Vennesland 2000, Gebauer and Moul 2001). If herons were not seen or heard within colonies, observers slowly approached the colony and entered, unless herons were heard at this time. Within colonies, observers searched for signs of earlier activity such as whitewash excrement and fresh eggshells below nests. When heron colonies appeared to be inactive after initial visits, they were visited again in June to re-evaluate inactivity status. Heron colonies and nests within colonies were considered to be active when herons were observed incubating, or chicks were observed within nests (Vennesland 2003b).

At active heron colonies, initial visits were used to sketch colony diagrams so that the reproductive fate of individual nests could be followed throughout the breeding season and to aid in nest location during subsequent colony visits. Efforts were made to conduct a complete count of the number of active nests within colonies throughout the breeding season. However, we were unable to obtain accurate counts within a few larger colonies within Region 2.

Estimating Number of Young Fledged

Active colonies were visited at least twice to count the number of young within nests; first when most young were <4 weeks old (May-June) and again when most young were 4-8 weeks old (July). Because the age of young varied within colonies, visits were targeted to assess nests when most young fell within these age groups. Within larger colonies (>25 nests; Vennesland 2003b) we randomly selected a sample of nests within the colony to monitor because censusing entire colonies was difficult and time consuming. We made an additional visit to colonies when several nests contained nestlings that were too young to assess for productivity estimates. The number of young fledged was estimated as the maximum number of 4-8 week old young observed within nests (Vennesland 2003b). Ideally, we counted young when they were 4-6 weeks old to avoid missing birds that were fledged and on branches away from nests. Nests that were active (see 2.2.1) and had 0 young in the nest >4 weeks old in late July were considered to have failed (=unsuccessful). Nests that had ≥1 young in the nest that were >4 weeks old in late July were considered to be successful.