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

Abstract

Once abundant, the Newfoundland Gray-cheeked Thrush (Catharus minimusminimus) has declined by as much as 95% since 1975. Underlying cause(s)of this population collapse are not known, although hypotheses includeloss of winter habitat and the introduction of red squirrels(Tamiasciurus hudsonicus) to Newfoundland. Uncertainties regardinghabitat needs are also extensive, and these knowledge gaps are animpediment to conservation. We investigated neighborhood (i.e., within115 m {[}4.1 ha]) and landscape scale (i.e., within 1250 m {[}490.8 ha])habitat associations of Gray-cheeked Thrush in a 200-km(2) study area inthe Long Range Mountains of western Newfoundland, where elevations rangefrom 300-600 m and landcover was a matrix of old growth fir forest, 6-to8-year-old clearcuts, coniferous scrub, bogs, and barrens. Thrushes wererestricted to elevations above similar to 375 m, and occurrence wasstrongly positively related to elevation. Occurrence was also positivelyrelated to cover of tall scrub forest at the neighborhood scale, and atthe landscape scale showed curvilinear relations with the proportion ofboth tall scrub and old growth forest that peaked with intermediateamounts of cover. Occurrence of thrushes was also highest when clearcutsmade up 60%-70% of neighborhood landcover, but was negatively relatedto cover of clearcuts in the broader landscape. Finally, occurrence washighest in areas having 50% cover of partially harvested forest (stripcuts or row cuts) at the neighborhood scale, but because this treatmentwas limited to one small portion of the study area, this finding may bespurious. Taken together, our results suggest selection for mixedhabitats and sensitivity to both neighborhood and landscape-scalehabitat. More research is needed on responses of thrushes to forestry,including use of older clearcuts, partially harvested stands, andprecommercially thinned clearcuts. Finally, restriction of thrushes tohigher elevations is consistent with the hypothesis that they have beenimpacted by squirrels, because squirrels were rare or absent at theseelevations.