Gray-cheeked Thrush (Catharus minimus minimus) distribution and habitat use in a montane forest landscape of western Newfoundland, Canada

Abstract

ABSTRACT. Once abundant, the Newfoundland Gray-cheeked Thrush (Catharus minimus minimus) has declined by as much as 95% since 1975. Underlying cause(s) of this population collapse are not known, although hypotheses include loss of winter habitat and the introduction of red squirrels (Tamiasciurus hudsonicus) to Newfoundland. Uncertainties regarding habitat needs are also extensive, and these knowledge gaps are an impediment to conservation. We investigated neighborhood (i.e., within 115 m [4.1 ha]) and landscape scale (i.e., within 1250 m [490.8 ha]) habitat associations of Gray-cheeked Thrush in a 200-km² study area in the Long Range Mountains of western Newfoundland, where elevations range from 300-600 m and landcover was a matrix of old growth fir forest, 6-to 8-yearold clearcuts, coniferous scrub, bogs, and barrens. Thrushes were restricted to elevations above ~375 m, and occurrence was strongly positively related to elevation. Occurrence was also positively related to cover of tall scrub forest at the neighborhood scale, and at the landscape scale showed curvilinear relations with the proportion of both tall scrub and old growth forest that peaked with intermediate amounts of cover. Occurrence of thrushes was also highest when clearcuts made up 60%-70% of neighborhood landcover, but was negatively related to cover of clearcuts in the broader landscape. Finally, occurrence was highest in areas having 50% cover of partially harvested forest (strip cuts or row cuts) at the neighborhood scale, but because this treatment was limited to one small portion of the study area, this finding may be spurious. Taken together, our results suggest selection for mixed habitats and sensitivity to both neighborhood and landscape-scale habitat. More research is needed on responses of thrushes to forestry, including use of older clearcuts, partially harvested stands, and precommercially thinned clearcuts. Finally, restriction of thrushes to higher elevations is consistent with the hypothesis that they have been impacted by squirrels, because squirrels were rare or absent at these elevations. Leur occurrence était aussi positivement associée aux peuplements de grands arbustes à l'échelle locale; à l'échelle du paysage, l'occurrence montrait des relations curvilignes avec la proportion de grands arbustes et de vieilles forêts et culminait en présence de valeurs intermédiaires de ces deux types forestiers. L'occurrence des grives était aussi maximale lorsque les coupes totales comptaient pour 60 à 70 % de la couverture terrestre locale, mais était négativement associée aux parterres de coupes totales à l'échelle du paysage. Enfin, l'occurrence était le plus élevée dans les endroits qui comportaient 50 % de couvert forestier partiellement récolté (coupes par bande ou par rangée) à l'échelle locale, mais étant donné que ce traitement était limité à une seule petite partie de l'aire d'étude, ce résultat pourrait se révéler faux. Pris dans leur ensemble, nos résultats semblent indiquer que les grives sélectionnent des milieux mixtes e...

Range‐wide populations of a long‐distance migratory songbird converge during stopover in the tropics

“…The apparently lower proportion of C. m. minimus in our samples may reflect either a differential migratory strategy between subspecies, that the range of C. m. minimus is smaller, or that there are fewer C. m. minimus due to population declines (Whitaker et al. , FitzGerald et al. ).…”

“…minimus breeds in Newfoundland and southeastern Labrador and is listed as threatened under the Newfoundland and Labrador Endangered Species Act because of precipitous population declines in recent decades (SSAC , Environment Canada , Whitaker et al. , FitzGerald et al. ).…”

“…Populations of the western breeding subspecies C. m. aliciae appear stable whereas populations of the eastern subspecies C. m. minimus have shown recent, drastic declines (Whitaker et al. , FitzGerald , FitzGerald et al. ).…”

Taxonomy and distribution of the imperilled Newfoundland Gray-cheeked Thrush, Catharus minimus minimus

“…We amplified and sequenced the entire 1041 base pairs (bp) mitochondrial NADH dehydrogenase 2 (ND2) gene from all individuals and two nuclear loci from subsets of individuals: a 518 bp region of the Z-chromosome gene ADAM-TS 6 from 44 Gray-cheeked and 30 Bicknell's Thrushes, and a 851 bp region of the autosomal beta-fibrinogen intron 7 (FIB7) from 37 Gray-cheeked and 22 Bicknell's Thrushes (Appendix 1). These genetic markers have distinct inheritance modes (ND2 is maternally inherited and haploid, FIB7 is biparentally inherited and diploid in both sexes, and ADAM-TS 6 is biparentally inherited but haploid in females and diploid in males) and have been shown to provide detailed, independent assessments of divergence at the population and species level (Winker and Pruett 2006, Jacobsen et al 2010, Hung et al 2013. ND2 was amplified and sequenced using primers from Sorenson et al (1999) and modified internal primers L5758 (5'-GGGTGAATAGGACTGAACCAAAC-3') and H5776 (5'-GAGATGGATGAGAAAGCTA-3').…”

“…Changes in breeding habitat associated with forest succession or forest harvesting could have caused local declines. However, much of the habitat used by thrushes is either unaffected by forest harvesting (e.g., conifer scrub) or is created by it (regenerating clearcuts; Whitaker et al 2015), and declines also occurred in Gros Morne National Park, a large protected area lacking industrial forestry (Lamberton 1976, Jacques Whitford Environment 1993, Rae 2014. In contrast, ecosystems on Newfoundland have been altered by the introduction of numerous species (e.g., Dodds 1983, Gosse et al 2011, Strong and Leroux 2014.…”