Retrospective Comparison of the Occurrence and Abundance of Rusty Blackbird in the Mackenzie Valley, Northwest Territories
Rusty Blackbird is listed as a species of "special concern" by the Committee On the Status of Endangered Wildlife In Canada, and has shown steep population declines in recent decades. Forty-five locations with historical survey data from the 1970s in the Mackenzie Valley, Northwest Territo...
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2007
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ftdoajarticles:oai:doaj.org/article:b62a035395844e1e93031676b803b645 2023-05-15T17:09:43+02:00 Retrospective Comparison of the Occurrence and Abundance of Rusty Blackbird in the Mackenzie Valley, Northwest Territories Craig S. Machtans Steven L. Van Wilgenburg Lindsay A. Armer Keith A. Hobson 2007-06-01T00:00:00Z https://doi.org/10.5751/ACE-00106-020103 https://doaj.org/article/b62a035395844e1e93031676b803b645 EN eng Resilience Alliance http://www.ace-eco.org/vol2/iss1/art3/ https://doaj.org/toc/1712-6568 1712-6568 doi:10.5751/ACE-00106-020103 https://doaj.org/article/b62a035395844e1e93031676b803b645 Avian Conservation and Ecology, Vol 2, Iss 1, p 3 (2007) COSEWIC Euphagus carolinus Mackenzie Valley population change Rusty Blackbird species at risk Plant culture SB1-1110 Environmental sciences GE1-350 Plant ecology QK900-989 article 2007 ftdoajarticles https://doi.org/10.5751/ACE-00106-020103 2022-12-31T07:49:27Z Rusty Blackbird is listed as a species of "special concern" by the Committee On the Status of Endangered Wildlife In Canada, and has shown steep population declines in recent decades. Forty-five locations with historical survey data from the 1970s in the Mackenzie Valley, Northwest Territories, Canada were revisited in 2006 to check for changes in the occurrence or abundance of Rusty Blackbird. Our retrospective analysis revealed a number of analytical challenges for such comparisons that we describe. The number of lakes on which this species occurred does not appear to have declined significantly in the past three decades when a correction for survey duration was applied. The range-wide decline of 5.1%/yr based on Christmas Bird Count data would have resulted in 2006 occupancy at ≈5 lakes. We estimate that with correction this would have increased to ≈26. However, naive or unadjusted analyses with a Chi-squared test showed a significant decline. A simulated resampling of the historical data was performed using a repeatability factor of 62% that was derived from a subset of historical lakes that was visited twice in the 1970s. Only 8 of 13 lakes resurveyed had the same results on both historical visits. Our unadjusted 2006 results are a likely outcome, i.e., a 14.9% chance of finding this result, when this repeatability factor is considered, and the likelihood of no change is higher when our corrected data are considered. The possibility of double counting in the historical data further reduced the likelihood of a large decline in relative abundance. Therefore, Rusty Blackbird occurrence does not appear to have changed significantly in the past 33 yr in the Mackenzie Valley. We conclude with a qualitative discussion that supports the notion that declines in the southern parts of their range may be a large factor in the observed rates of population decline. Article in Journal/Newspaper Mackenzie Valley Northwest Territories Directory of Open Access Journals: DOAJ Articles Northwest Territories Canada Mackenzie Valley ENVELOPE(-126.070,-126.070,52.666,52.666) Avian Conservation and Ecology 2 1 |
institution |
Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
COSEWIC Euphagus carolinus Mackenzie Valley population change Rusty Blackbird species at risk Plant culture SB1-1110 Environmental sciences GE1-350 Plant ecology QK900-989 |
spellingShingle |
COSEWIC Euphagus carolinus Mackenzie Valley population change Rusty Blackbird species at risk Plant culture SB1-1110 Environmental sciences GE1-350 Plant ecology QK900-989 Craig S. Machtans Steven L. Van Wilgenburg Lindsay A. Armer Keith A. Hobson Retrospective Comparison of the Occurrence and Abundance of Rusty Blackbird in the Mackenzie Valley, Northwest Territories |
topic_facet |
COSEWIC Euphagus carolinus Mackenzie Valley population change Rusty Blackbird species at risk Plant culture SB1-1110 Environmental sciences GE1-350 Plant ecology QK900-989 |
description |
Rusty Blackbird is listed as a species of "special concern" by the Committee On the Status of Endangered Wildlife In Canada, and has shown steep population declines in recent decades. Forty-five locations with historical survey data from the 1970s in the Mackenzie Valley, Northwest Territories, Canada were revisited in 2006 to check for changes in the occurrence or abundance of Rusty Blackbird. Our retrospective analysis revealed a number of analytical challenges for such comparisons that we describe. The number of lakes on which this species occurred does not appear to have declined significantly in the past three decades when a correction for survey duration was applied. The range-wide decline of 5.1%/yr based on Christmas Bird Count data would have resulted in 2006 occupancy at ≈5 lakes. We estimate that with correction this would have increased to ≈26. However, naive or unadjusted analyses with a Chi-squared test showed a significant decline. A simulated resampling of the historical data was performed using a repeatability factor of 62% that was derived from a subset of historical lakes that was visited twice in the 1970s. Only 8 of 13 lakes resurveyed had the same results on both historical visits. Our unadjusted 2006 results are a likely outcome, i.e., a 14.9% chance of finding this result, when this repeatability factor is considered, and the likelihood of no change is higher when our corrected data are considered. The possibility of double counting in the historical data further reduced the likelihood of a large decline in relative abundance. Therefore, Rusty Blackbird occurrence does not appear to have changed significantly in the past 33 yr in the Mackenzie Valley. We conclude with a qualitative discussion that supports the notion that declines in the southern parts of their range may be a large factor in the observed rates of population decline. |
format |
Article in Journal/Newspaper |
author |
Craig S. Machtans Steven L. Van Wilgenburg Lindsay A. Armer Keith A. Hobson |
author_facet |
Craig S. Machtans Steven L. Van Wilgenburg Lindsay A. Armer Keith A. Hobson |
author_sort |
Craig S. Machtans |
title |
Retrospective Comparison of the Occurrence and Abundance of Rusty Blackbird in the Mackenzie Valley, Northwest Territories |
title_short |
Retrospective Comparison of the Occurrence and Abundance of Rusty Blackbird in the Mackenzie Valley, Northwest Territories |
title_full |
Retrospective Comparison of the Occurrence and Abundance of Rusty Blackbird in the Mackenzie Valley, Northwest Territories |
title_fullStr |
Retrospective Comparison of the Occurrence and Abundance of Rusty Blackbird in the Mackenzie Valley, Northwest Territories |
title_full_unstemmed |
Retrospective Comparison of the Occurrence and Abundance of Rusty Blackbird in the Mackenzie Valley, Northwest Territories |
title_sort |
retrospective comparison of the occurrence and abundance of rusty blackbird in the mackenzie valley, northwest territories |
publisher |
Resilience Alliance |
publishDate |
2007 |
url |
https://doi.org/10.5751/ACE-00106-020103 https://doaj.org/article/b62a035395844e1e93031676b803b645 |
long_lat |
ENVELOPE(-126.070,-126.070,52.666,52.666) |
geographic |
Northwest Territories Canada Mackenzie Valley |
geographic_facet |
Northwest Territories Canada Mackenzie Valley |
genre |
Mackenzie Valley Northwest Territories |
genre_facet |
Mackenzie Valley Northwest Territories |
op_source |
Avian Conservation and Ecology, Vol 2, Iss 1, p 3 (2007) |
op_relation |
http://www.ace-eco.org/vol2/iss1/art3/ https://doaj.org/toc/1712-6568 1712-6568 doi:10.5751/ACE-00106-020103 https://doaj.org/article/b62a035395844e1e93031676b803b645 |
op_doi |
https://doi.org/10.5751/ACE-00106-020103 |
container_title |
Avian Conservation and Ecology |
container_volume |
2 |
container_issue |
1 |
_version_ |
1766065872271572992 |