Clearcutting and the breeding productivity of golden eagles (Aquila chrysaetos) in Västerbotten County

• Main Author: Trulsson, Amanda
• Format: Text
• Language: Swedish; English
• Published: 2019
• Subjects: Forestry production; Animal ecology; Nature conservation and land resources; Aquila chrysaetos; golden eagle; kungsörn
• Online Access: https://stud.epsilon.slu.se/14228/1/trulsson_a_190226.pdf

The golden eagle (Aquila chrysaetos) is red-listed as near threatened in Sweden, but there are many basic ecological and demographical parameters important for successful management and conservation that are unknown for the Swedish golden eagle population. Forestry, and especially clearcutting (or final cutting/felling or regeneration cutting/felling), the most common harvesting system in Sweden since the 1950’s, are likely important factors affecting the Swedish golden eagle population, but exactly how is largely unknown. Effects of both clearcutting and forestry in general on golden eagles and their breeding productivity may be positive, negative, direct and indirect. In this thesis I have investigated the effects of clearcutting on the breeding productivity of golden eagles between 2002 to 2016, 15 years in total, in 143 territories in Västerbotten County (each territory inventoried in at least 8 of the years of the study period). Golden eagle breeding data was provided by Kungsörn Sverige Västerbotten, and clear-cut data was provided by the Swedish Forest Agency. Analyses were made in three groups: mountain territories, lowland territories, and all territories together (lowland + mountains). Using simple linear and 2ⁿᵈ order polynomial regressions in the program R, I made territory-level regressions of the average number of nestlings born per year (in three breeding productivity variables: year with territory visited by surveyors, occupied by golden eagles, and with breeding golden eagles, respectively) on the cumulatively summed area of clear-cuts weighted by territory area (in three clear-cut variables: ordinary cumulative sum, a.k.a. including clear-cuts made over the entire study period except for in 2016, thus including clear-cuts up to at least 15 years of age, and successively excluding clear-cuts when they reach 5 and 10 years, respectively). Clear-cut area was extracted from two modelled territory sizes, ca 5 km2 and ca 30 km2, which correspond to the minimum and maximum core area sizes of a golden ...