Update on the Status and Breeding Phenology of the Timberline Sparrow (Spizella breweri taverneri) in Alaska

In July 2020 we located 10 singing Timberline Sparrows [Spizella (breweri) taverneri] in the region of Gold Hill, Nutzotin Mountains, east-central Alaska. All birds were on southeast-facing slopes in the ecotone between subalpine scrub and alpine tundra, to which habitat breeding Timberline Sparrows seem narrowly confined. The population’s estimated density of 0.77 birds/km2 was similar to that at the time of its discovery in 1994. We located the first active nest of the Timberline Sparrow reported for Alaska, ~0.3 m above the ground in a shrubby resin birch (Betula glandulosa). An observation of young fledged on 11 or 12 July 2020 implies egg laying in the third week of June, later than the beginning of the breeding season of Spizella (breweri) breweri.

New Allometric Equations for Arctic Shrubs and Their Application for Calculating the Albedo of Surfaces with Snow and Protruding Branches

Arctic shrubs reduce surface albedo in winter when branches protrude above the snow. To calculate the albedo of those mixed surfaces, the branch area index (BAI) of Arctic shrubs needs to be known. Moreover, an exposed-vegetation function is required to determine the BAI for protruding branches only. This study used a structural analysis of 30 Betula glandulosa shrubs, sampled near Umiujaq, northern Quebec, to (i) establish an allometric relationship between shrub height and BAI and (ii) determine a specific exposed-vegetation function for Arctic shrubs. The spectral albedo (400–1080 nm) of mixed surfaces was then simulated with the equations derived from this study and validated with in situ measured spectra. Shrubs were sampled from two sites, one along the coast and the other in a nearby valley. The shrub height–BAI relationship varied between both sites. BAI values of shrubs growing in the wind-sheltered valley were 30%–50% lower. The exposed-vegetation function obtained here differed from the linear functions found in the literature. The linear functions strongly overestimated the BAI of exposed branches. Albedo was well simulated with an accuracy of 3% when using an allometric relationship adapted to the environmental conditions of our study site. However, simulated albedo values were consistently higher than field measurements, probably because radiation absorbed by impurities and buried branches was neglected in the model. We conclude that specific exposed-vegetation and allometric equations need to be implemented in models to accurately simulate the albedo of mixed snow–shrub surfaces.