Population fluctuations and regulation in great snipe: a time-series analysis

• Published in: The Journal of animal ecology Vol. 76; no. 4; pp. 740 - 749
• Main Authors: KÖLZSCH, ANDREA, SÆTHER, STEIN ARE, GUSTAFSSON, HENRIK, FISKE, PEDER, HÖGLUND, JACOB, KÅLÅS, JOHN ATLE
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.07.2007; British Ecological Society; Blackwell Publishing Ltd; Blackwell
• Subjects: Animal and plant ecology; Animal ecology; Animal Migration - physiology; Animal populations; Animal, plant and microbial ecology; Animals; Aves; Biologi; Biological and medical sciences; Biology; Birds; Bootstrap; Breeding; Charadriiformes - growth & development; Charadriiformes - physiology; Covariate; Demecology; Density dependence; Ecology; Environment; environmental covariates; Female; Fluctuations; Fundamental and applied biological sciences. Psychology; Gallinago media; General aspects; Grouse; Likelihood ratio test; Limicolous; Male; Males; NATURAL SCIENCES; NATURVETENSKAP; Norway; Parametric Bootstrap Likelihood Ratio test; Population Density; Population Dynamics; Population ecology; Population growth; Population regulation; Population size; Precipitation; Predatory Behavior; Seasons; Sex Ratio; Stochastic Processes; Time series; Time series models; Vertebrata; Norway; Population regulation; Fluctuations; Time series; Limicolous; environmental covariates; Covariate; Vertebrata; Parametric Bootstrap Likelihood Ratio test; Gallinago media; Likelihood ratio test; Bootstrap; Density dependence; Population dynamics; Aves
• ISSN: 0021-8790; 1365-2656; 1365-2656
• DOI: 10.1111/j.1365-2656.2007.01246.x

1. During the last centuries, the breeding range of the great snipe Gallinago media has declined dramatically in the western part of its distribution. To examine present population dynamics in the Scandinavian mountains, we collected and analysed a 19-year time series of counts of great snipe males at leks in central Norway, 1987-2005. 2. The population showed large annual fluctuations in the number of males displaying at lek sites (range 45-90 males at the peak of the mating season), but no overall trend. 3. We detected presence of direct density-dependent mechanisms regulating this population. Inclusion of the density-dependent term in a Ricker-type model significantly improved the fit with observed data (evaluated with Parametric Bootstrap Likelihood Ratio tests and Akaike's Information Criterion for small sample size). 4. An analysis of (a number of a priori likely) environmental covariates suggests that the population dynamics were affected by conditions influencing reproduction and survival of offspring during the summer, but not by conditions influencing survival at the wintering grounds in Africa. This is in contrast to many altricial birds breeding in the northern hemisphere, and supports the idea that population dynamics of migratory nidifugous birds are more influenced by conditions during reproduction. 5. Inclusion of these external factors into our model improved the detectability of density dependence. This illustrates that allowing for external effects may increase statistical power of density dependence tests and thus be of particular importance in relatively short time series. 6. In our best model of the population dynamics, two likely density-independent offspring survival covariates explained 47·3% of the variance in great snipe numbers (predation pressure estimated by willow grouse reproductive success and food availability estimated by the amount of precipitation in June), whereas density dependence explained 35·5%. Demographic stochasticity and unidentified environmental stochasticity may account for the remaining 17·2%.