Great blue heron (fannini subspecies) COSEWIC assessement and update status report: chapter 13

Technical summary

Ardea herodias fannini
Great Blue Heron fannini subspecies

Grand Héron de la sous-espèce fannini

Range of Occurrence in Canada: British Columbia


Extent and area information

Extent of occurrence (EO) (km 2 )
From GIS analysis – minimum polygon around entire Canadian range
244 000 km 2
Specify trend in EO
Unknown, possibly declining on peripheries of range
Are there extreme fluctuations in EO?
No
Area of occupancy (AO) (km 2 )
From Geographic Information System (GIS) analysis – see Figure 2
188 000 km 2
Specify trend in AO.
Unknown, possibly declining on peripheries of range (outside of lower Fraser Valley)
Are there extreme fluctuations in AO?
No
Number of known or inferred current locations.
49 nesting locations (2005)
Specify trend in #.
Unknown
Are there extreme fluctuations in number of locations?
Not likely
Specify trend in area, extent or quality of habitat.
Declining


Population information

Generation time (average age of parents in the population).
Estimated at 5.6 years
Number of mature individuals.
Est. 4000-5000
Total population trend:
Variable - declines based on Christmas Bird Count data over three generations (below), increasing based on Coastal Waterbird Surveys over recent five-year period.
% decline over the last 10 years or 3 generations.
based on Christmas Bird Count (CBC) data with a 5 (lower number) or 6 (higher)-year generation time
19-26% (CBC), but increasing based on Coastal Waterbird Surveys
Are there extreme fluctuations in number of mature individuals?
Not likely
Is the total population severely fragmented?
For breeding locations – Range wide, No; In Lower Fraser Valley, Yes
Specify trend in number of populations.
Unknown
Are there extreme fluctuations in number of populations?
No
List populations with number of mature individuals in each:
Unknown


Threats (actual or imminent threats to populations or habitats)

Primary threats are from Bald Eagle predation, human disturbance and habitat destruction. Human influences are especially acute in the lower Fraser Valley (the centre of the subspecies’ range).


Rescue effect (immigration from an outside source)

Status of outside population(s)? USA (Washington State):
declining
Is immigration known or possible?
Yes
Would immigrants be adapted to survive in Canada?
Yes
Is there sufficient habitat for immigrants in Canada?
Unknown, habitat is declining near U.S. border (lower Fraser Valley)
Is rescue from outside populations likely?
Unknown, but may be limited because declining in the U.S.


Quantitative analysis

n/a


Current status

Committee on the Status of Endangered Wildlife in Canada (COSEWIC): Special Concern (1997 and 2008)


Status and reasons for designation

Status: Special concern
Alpha-numeric code: Not applicable


Reasons for Designation: In Canada, this subspecies is distributed along the coast of British Columbia with a relatively small population that is concentrated at a few breeding colonies in southern British Columbia. There is evidence of declines in productivity and it is unclear whether the population is stable or declining. Threats from eagle predation, habitat loss and human disturbance are ongoing, particularly in the southern part of the range where concentrations of birds are highest.


Applicability of criteria

Criterion A (Declining Total Population): Not applicable. Does not meet criterion.

Criterion B (Small Distribution, and Decline or Fluctuation): Not applicable. Does not meet criterion.

Criterion C (Small Total Population Size and Decline): May meet Threatened C1 if Christmas Bird Count trends are used to predict future declines.

Criterion D (Very Small Population or Restricted Distribution): Not applicable. Does not meet criterion.

Criterion E (Quantitative Analysis): None.

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