2023 Early Hearing Detection & Intervention Conference
March 5-7, 2023 • Cincinnati, OH
9/26/2018 | 1:55 PM - 2:10 PM | Determinants of Annual Breeding Success in Boreal Forest Grouse: Preliminary Results from a Long-Term Study of Capercaillie (Tetrao urogallus) and Black Grouse (T. tetrix) in Norway | Eccles Conference Center Auditorium
Determinants of Annual Breeding Success in Boreal Forest Grouse: Preliminary Results from a Long-Term Study of Capercaillie (Tetrao urogallus) and Black Grouse (T. tetrix) in Norway
Forest grouse are relatively long-lived birds with high reproductive potential. Still, many species struggle to sustain viable populations, typically explained by high losses during nesting and brood rearing. Here we report on a 40-year survey of synchronously fluctuating populations of capercaillie and black grouse at the Varaldskogen study area, southeast Norway, inspecting potential factors presumed to be important for the breeding success in these two species. Preliminary analyses show that warm summers together with numbers of small rodents were principal determinants of annual breeding success. Cyclic small rodents presumably influenced breeding success through relaxed predation pressure in peak vole years and higher predation in crash years, whereas early spring and warm summers presumably increased female condition and chick survival, respectively. Other contributing factors were number of medium-sized mammalian predators (red fox and pine marten) and the abundance of insect larvae available on bilberry, which decreased and increased breeding success, respectively. Surprisingly, post-hatch precipitation had little explanatory power, neither was there any effect of the proportion of yearling females in the populations. Thus, each year, breeding success varied with the combination of spring/early summer temperature and abundances of voles, meso-predators and insect larvae posthatch, with the temporal variation in small rodents and temperature having most impact. During the study period, breeding success of both species increased significantly (Wegge & Rolstad 2017), mostly due to increasing spring and early summer temperatures, but possibly also due to increasing vole numbers, both of which may have contributed to ease the predation pressure.
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Presenters/Authors
Per Wegge
(), per.wegge@nmbu.no ;
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Jørund Rolstad
(), jorund.rolstad@nibio.no;
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