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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