Loggerhead shrike COSEWIC assessment and status report: chapter 12
Technical Summary
Lanius ludovicianus excubitorides
Loggerhead Shrike excubitoridessubspecies – Pie-grièche migratrice de la sous-espèceexcubitorides
Range of Occurrence in Canada:
Alberta, Saskatchewan, Manitoba
Extent and Area information
extent of occurrence (EO) (km²)
ca 300,000 km²
specify trend (decline, stable, increasing, unknown)
Decline
are there extreme fluctuations in EO (> 1 order of magnitude)?
No
area of occupancy (AO) (km²)
ca. 5000 to 10,000 km²
specify trend (decline, stable, increasing, unknown)
Decline
are there extreme fluctuations in AO (> 1 order magnitude)?
No
number of extant locations
Not applicable
specify trend in # locations (decline, stable, increasing, unknown)
are there extreme fluctuations in # locations (>1 order of magnitude)?
habitat trend: specify declining, stable, increasing or unknown trend in area, extent or quality of habitat
Unknown
Population information
generation time (average age of parents in the population) (indicate years, months, days, etc.)
2
number of mature individuals (capable of reproduction) in the Canadian population (or, specify a range of plausible values)
ca. 20,000
total population trend: specify declining, stable, increasing or unknown trend in number of mature individuals
Declining
if decline, % decline over the last/next 10 years or 3 generations, whichever is greater (or specify if for shorter time period)
37% over 10 years
(83% since 1968)
(BBS data)
are there extreme fluctuations in number of mature individuals (> 1 order of magnitude)?
No
is the total population severely fragmented (most individuals found within small and relatively isolated (geographically or otherwise) populations between which there is little exchange, i.e., < 1 successful migrant / year)?
No
list each population and the number of mature individuals in each
-
specify trend in number of populations (decline, stable, increasing, unknown)
-
are there extreme fluctuations in number of populations (>1 order of magnitude)?
-
Threats (actual or imminent threats to populations or habitats)
- Loss of native grasslands and pastureland in breeding, migration and wintering grounds
- Degradation of habitat due to cattle grazing
- Pesticides, particularly DDT and dieldrin used on insect prey, occur in high concentration in shrikes and have been implicated in population decline
- decreasing breeding success at low population levels
Rescue Effect (immigration from an outside source)
Moderate
Status of outside population(s)?
USA: Wisconsin: Endangered
Minnesota: Threatened
does species exist elsewhere (in Canada or outside)?
Yes
status of the outside population(s)?
Stable, declining
is immigration known or possible?
Yes
would immigrants be adapted to survive here?
Yes
is there sufficient habitat for immigrants here?
Yes, but declining
Quantitative Analysis
Other Status
- COSEWIC: Threatened (1986)
Status and Reasons for Designation
Status: Threatened
Alpha-numeric code: A2bc
Reasons for Designation: This raptorial songbird has suffered significant (more than 80 %) population declines over the past 35 years. These declines have been linked to loss of native prairie and pastureland habitats and pesticide residues.
Applicability of Criteria
- Criterion A (Declining Total Population): Threatened A2bc applies, since Breeding Bird Survey data suggest a 10-year decline of 37% and the causes for this decline have not ceased.
- Criterion B (Small Distribution, and Decline or Fluctuation): Not applicable since AO and EO are too large
- Criterion C (Small Total Population Size and Decline): Not applicable since population is too large
- Criterion D (Very Small Population or Restricted Distribution): Not applicable because distribution is not restricted and population too large
- Criterion E (Quantitative Analysis): Not done.
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