Half-moon hairstreak (Satyrium semiluna) COSEWIC assessment and status report: chapter 13

Technical summary

Satyrium semiluna
Half-moon Hairstreak

Porte-queue demi-lune

Range of occurrence in Canada: British Columbia (BC) and Alberta (AB)

Extent and area information

Extent of occurrence.

485 km ²

Specify trend.

Unknown, probably declining

Are there extreme fluctuations in EO?

Area of occupancy.

<250 km ² , could be as little as 30 km ²

Specify trend.

Unknown

Are there extreme fluctuations in AO?

Unknown, but unlikely

Number of extant locations.

12 sites, likely representing 7 populations

Specify trend in # locations.

Unknown, new locations have recently been found, probably as a result of increased search effort

Are there extreme fluctuations in # locations?

Habitat trend:

Declining

Population information

Generation time.

1 year

Number of mature individuals in the Canadian population.

Unknown, plausibly as many as 8 000 to 25 000, but lower limit could be considerably lower

Total population trend.

Unknown, likely declining

If decline, % decline over the last/next 10 years or 3 generations, whichever is greater (or specify if for shorter time period).

Not applicable

Are there extreme fluctuations in number of mature individuals?

Yes in AB population;
unlikely in BC population

Is the total population severely fragmented?

Yes

List each population and the number of mature individuals in each.

Waterton Lakes -plausibly <1 000 to 10 000
Anarchist Mtn. - unknown
Keremeos Columns - unknown
Kilpoola grasslands - unknownMt. Kobau - unknown
Richter Pass - unknown
White Lake - unknown

Specify trend in number of populations.

Unknown, may be declining

Are there extreme fluctuations in number of populations?

Unknown, but probably not

Threats

Intensive livestock grazing
Loss of habitat to agriculture, infrastructure development and other uses
One location could be affected by expansion of an aggregate pit
Habitat change by invading knapweed
Habitat change and direct mortality from knapweed control activity

Rescue effect: Moderate

Does species exist elsewhere?

Yes

Status of the outside population(s)?

US: Apparently secure (S4)

Is immigration known or possible?

Possible in BC population, but generally this genus is thought to be a poor disperser; highly unlikely in AB population

Would immigrants be adapted to survive here?

Probably

Is there sufficient habitat for immigrants here?

Probably, although key habitat requirements remain unknown

Quantitative Analysis

Not applicable

Current status

Committee on the Status of Endangered Wildlife in Canada (COSEWIC): Endangered (2006)
NatureServe: G4, N1N2 in Canada, S1 in BC, SH (should be updated to S1?) in AB, S4 in Washington and Montana, and SNR in Idaho.
General Status: may be at risk

Status and reasons for designation

Status: Endangered

Alpha-numeric code: B1ab(iii,v) + 2ab(iii,v)

Reasons for Designation: The butterfly occurs as disjunct populations in two small, restricted areas at the northern extreme of the species’ range. The species’ population has likely declined in the past as a result of habitat loss. Both populations continue to be threatened by habitat loss and degradation. In British Columbia the species occurs in an area under severe pressure for development. In both Alberta and British Columbia, invasive weeds also pose a serious threat.

Applicability of criteria

Criterion A (Declining Total Population): no data.

Criterion B (Small Distribution, and Decline or Fluctuation):

the extent of occurrence is smaller than 5000 km² (485 km²) – 1
the area of occupancy is smaller than 500 km² (smaller than 250 km²) – 2
the population is severely fragmented – a
and there are continuing declines in the quality of the habitat – b(iii)
resulting in inferred declines in the number of mature individuals – b(v)

Criterion C (Small Total Population Size and Decline): Likely meets Threatened C2a(i):

the number of mature individuals is fewer than 10 000
there are no data on decline rates
but continuing decline in population size are inferred on the basis of habitat loss and degradation – 2
with a population structure – a
where it is likely that in low population years, the situation exists where no population contains more than 1000 mature individuals – i
and although the Alberta population undergoes extreme fluctuations in number of mature individuals, there is no evidence to support extreme fluctuations in the overall population.

Criterion D (Very Small Population or Restricted Distribution): Not applicable.

Criterion E (Quantitative Analysis): No data.

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Date modified:: 2016-04-26

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