Barn Owl (Tyto alba)

Transcription

1 COSSARO Candidate Species at Risk Evaluation Form for Barn Owl (Tyto alba) Committee on the Status of Species at Risk in Ontario (COSSARO) Assessed June 2010 by COSSARO as Endangered June 2010 Final

2 PART 1 COSSARO Candidate Species at Risk Evaluation Form June 2010 Barn Owl (Tyto alba) Current Designations: GRANK G5 NRANK Canada N3 COSEWIC eastern population: Endangered (May 2000) SARA Endangered (Schedule 1) General Status Canada Sensitive ESA 2007 Endangered SRANK S1 General Status Ontario At Risk Distribution and Status Outside Ontario: Distribution almost worldwide. Two designatable units in Canada, eastern and western. ELIGIBILITY CRITERIA Native Status Yes Native in Canada, occurrences in Quebec, Ontario and British Columbia Taxonomic Distinctness Yes Considered a valid species in all recent taxonomic treatments. No clear genetic answer to question about whether east and west populations are distinct. Designatable Units One designatable unit in Ontario, two in Canada PRIORITY-SETTING CRITERIA Recent Arrival No Long known as a native bird Non-resident No 1. Global Rank Not in any category. G5 2. Global Decline Not in any category. 3. Northeastern North America Ranks PRIMARY CRITERIA (rarity and declines) 2

3 THR (Ranked S1, S2, SH, or SX in 13 of 19 (68%) of Northeastern North American jurisdictions in which it occurs and is ranked. The species is ranked S3 in an additional 6 jurisdictions.) 4. Northeastern North America Decline END (The Barn Owl is a species of Special Concern in 5 (Vermont, Pennsylvania, New York, Maryland, and Massachusetts), Threatened in 4 (Rhode Island, Ohio, Connecticut, and Ontario), and Endangered in 2 (Michigan and Iowa) northeastern jurisdictions (Appendix 1; Blodget 1989). Based on the number of northeastern jurisdictions where the species is ranked S1 or S2, or is listed as Threatened or Endangered, it appears that Barn Owls are still in decline. Therefore, Endangered status is presumed for this criterion in the absence of information regarding population decline from Natural Heritage Programs. 5. Ontario Occurrences END (Ontario population 20 mature birds (Badzinski 2007)). 6. Ontario Decline END (Virtually all sites checked in 2008 for which previous (1986 or 2001) population counts are estimates are available, have declined (Table 1 in COSEWIC 2010). Twelve of 25 (48%) Element Occurrence records in the NHIC database are considered extirpated and at least a couple of others have not been recently checked and may be extirpated.) 7. Ontario s Conservation Responsibility Not in any category (Ontario makes up <5% of the species global range (COSEWIC 2010).) SECONDARY CRITERIA (threats and vulnerability) 1. Population Sustainability Not in any category 2. Lack of Regulatory Protection for Exploited Wild Populations Not in any category (Barn Owls are not migratory, and are protected in Ontario by FWCA and SARA.) 3. Human Threats END (Loss of nesting habitats (old barns and silos), loss of foraging habitat and mortality along roads are important threats to the survival of Barn Owls in Ontario.) 4. Specialized Life History or Habitat-use Characteristics END (The short adult life span, puts Barn Owls at risk, particularly in light of the loss of habitat for nesting and foraging. Although Barn Owls can be prolific breeders, they are not achieving high levels of reproduction in Ontario.) 3

4 COSSARO CRITERIA MET (primary/secondary) ENDANGERED 3/2 THREATENED 1/0 SPECIAL CONCERN 1/0 Barn Owl (Tyto alba) Summary One of the two Canadian populations occurs in Ontario (consisting of ~20 adult birds), the other is in British Columbia. Although this species has high reproductive potential because they lay large clutches and may reproduce at any time of the year, adults live less than 3 years. Even though in British Columbia and elsewhere in their range these birds regularly use nest boxes, this has not happened in Ontario. In Ontario, birds have suffered from loss of nesting sites (old barns and silos) and foraging habitat (due to the spread of agriculture and succession). There has been no change in the population in Ontario since the last assessment. Changes in land use and farming practices are the main threats to the population in Ontario. This species is Endangered in Ontario. Information Sources Badzinski, D.S Barn Owl. Pp in Cadman, M.D., D.A. Sutherland, G.G. Beck, D. Lepage, and A.R. Couturier, eds. Atlas of the Breeding Birds of Ontario, Bird Studies Canada, Environment Canada, Ontario Field Ornithologists, Ontario Ministry of Natural Resources, and Ontario Nature, Toronto, xxii pp. Blodget, B.G Common Barn-owl. Pp in Proc. Northeast Raptor Management Symposium and Workshop (B. Giron Pendleton, ed.). National Wildlife Federation Scientific and Technical Series No. 13. COSEWIC Update Status Report on Barn Owl (Tyto alba) Eastern Population and Western Population. Committee on the Status of Endangered Wildlife in Canada. Ottawa. 4

5 Appendix 1 NORTHEASTERN NORTH AMERICA RANK, STATUS AND DECLINE CT S2 DE S3 IL S1S2 IN S2 IA S1B KY S3 LB MA S2B, S2N MB MD S3 ME MI S1 MN NB NF NH NJ S3B NS NY S1S2 OH S2 ON S1 PA S3B, S3N PE QC RI S1B, S1N VA S3B, S3N VT S1B, S1N WI S1B, S1N WV S2B, S2N Occurs as a native species in 19 of 29 northeastern jurisdictions S rank or equivalent information available for 19 of 19 jurisdictions = 100 % S1, S2, SH or SX in 13 of 19 = 68 % 5

6 PART 2 Ontario Evaluation Using COSEWIC Criteria Regional (Ontario) COSEWIC Criteria Assessment Criterion A Decline in Total Number of Mature Individuals Not in any category: no evidence of decline over at least 10 years Criterion B Small Distribution and Decline or Fluctuation Not in any category Criterion C Small and Declining Number of Mature Individuals Not in any category Criterion D Very Small or Restricted Total Population Endangered (D1) [ 20 adults in the population] Criterion E Quantitative Analysis No data available Rescue Effect There remains the possibility that vagrant individuals from populations south of Lake Erie may end up in Ontario, but there is no evidence of this having happened in at least 10 years. 6