COSEWIC assessment and status report on the Red Crossbill percna subspecies Loxia curvirostra percna in Canada
- Assessment Summary
- Executive Summary
- COSEWIC History, Mandate, Membership and Definitions
- Lists of Figures, Tables and Appendices
- Species Information
- Population Sizes and Trends
- Limiting Factors and Threats
- Special Significance of the Species
- Existing Protection or Other Status
- Summary of Status Report
- Technical Summary
- Acknowledgements and Literature Cited
- Biographical Summary of the Report Writers, Authorities Contacted, and Collections Examined
Loxia Curvirostra Percna
The Red Crossbill percna subspecies is a medium sized finch found primarily in conifer forests. Like other crossbills, it has crossed mandibles that allow the bird to pry open conifer cone scales to access the seeds within. Compared to other Red Crossbills in North America, the percna subspecies has a relatively stout and deep bill, and a dusky colouration.
The commonly used scientific name of this subspecies is Loxia curvirostra percna (the subspecies has previously been referred to as L. c. pusilla by several authors). There are at least seven other types of Red Crossbills that occur in North America, which exhibit differences in vocalizations and morphology. Recent research has suggested that each of the types of North American Red Crossbills are likely species, and not subspecies as they have been traditionally considered, because they remain reproductively isolated even when they are not geographically separated.
Red Crossbill types are found throughout the world’s boreal forests, and in more southerly regions with coniferous habitat. Coniferous forests represent the core habitat and range for Red Crossbills. Occasionally, however, they “irrupt” into non-conifer locations in search of food when conifer seeds are in short supply. In North America, different types of Red Crossbills are widely distributed across the continent, with a range that follows the distribution of boreal forests and other coniferous habitat. In Canada, their distribution ranges from British Columbia to the Maritimes and Newfoundland.
Nests of the percna subspecies have only been found on insular Newfoundland. The birds apparently move off the island occasionally, and some large-billed birds that could be percna have been observed and collected in the Maritimes, New England, and Quebec. The subspecies is, however, difficult to identify in the field, so it is not certain that all Red Crossbill sightings from Newfoundland represent the percna subspecies.
Red Crossbills are extreme boreal forest specialists as a result of their bill morphology. Like other crossbills, they have co-evolved with their conifer food sources, and all large-billed crossbills, likely including the Red Crossbill percna subspecies, are associated with pine forests. Prime Red Crossbill habitat is mature, cone-productive forest. Red and White Pine stands were formerly important habitat for Red Crossbills, but now have severely restricted distributions in Newfoundland. Mature Black Spruce and Balsam Fir forests, also important Red Crossbill habitat, are becoming increasingly fragmented and threatened from harvesting. Forest fires and insect damage have also acted to reduce conifer seed abundance across the island. Forestry companies currently hold the logging tenures for 69% of the Crown land on insular Newfoundland.
Red Crossbills are monogamous, forming pair bonds but nesting in loose aggregations and foraging in large flocks. They have a flexible breeding strategy, whereby nesting can occur in colder months if conifer seeds are abundant and they possess physiological adaptations that allow them to thrive in cold climates. Crossbills undertake nomadic movements of various scales in search of abundant conifer seed resources, though some island populations, which might include percna, tend to exhibit more sedentary patterns. Survival is closely tied to the availability of conifer seeds, and birds at times face starvation if cone crops fail across wide geographic areas. Other causes of mortality for the percna subspecies include death from vehicle strikes and predation, as well as potential competition for conifer seeds and nest predation by introduced Red Squirrels.
Population Sizes and Trends
Red Crossbills were once relatively common in Newfoundland. In recent decades, they have undergone a precipitous and continuous decline. Currently, they are very rare across the island, and are sighted very infrequently and erratically on both formal and informal surveys. A rough estimate of the current population size, 500 – 1500 individuals, is based on field experience, Christmas Bird Counts, Breeding Bird Surveys and other surveys that suggest that the order of magnitude of the population could be between 100s and low thousands. Much uncertainty is associated with this estimate, due to the relatively limited sampling across the island, the difficulties in counting nomadic birds like Red Crossbills, the lack of recent breeding observations, the difficulty in identifying crossbill subspecies in the field, and the possibility that Red Crossbills may move between the island of Newfoundland and the mainland.
Limiting Factors and Threats
Boreal forest habitat degradation and change are significant and current threats to the survival of Red Crossbills in Newfoundland. Other threats include potential competition with and predation by Red Squirrels.
Special Significance of the Species
The Red Crossbill percna subspecies, is a distinctive taxonomic group. The subspecies’ high level of specialization on the seeds of conifer trees makes their presence a signal of a healthy, mature and productive native forest. They are endemic to insular Newfoundland and intimately associated with local boreal forest ecosystems.
Existing Protection or Other Status Designations
The Red Crossbill is protected under the Migratory Bird Convention Act. NatureServe designates Red Crossbills in Newfoundland as imperilled/vulnerable. Populations of Red Crossbills are generally robust in western parts of the country, with most declines recorded in the northeast. Federally and provincially protected lands in Newfoundland account for approximately 8% of the area of the island, a portion of which is expected to offer habitat for Red Crossbills.
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