Abstract
AbstractThe Whiskered Tern population in Poland has rapidly increased from 40 breeding pairs in 1990 to over 1,600 in 2007, with strongest local population in the Upper Vistula River Valley. Owing to rather low pre-breeding and adult apparent survival rates estimated for this population (0.54 and 0.80, respectively) and a delay in accession to reproduction (recruitment completed at age 3), matrix modelling indicated an intrinsic growth rate ofλcalc = 1.02. Observed growth rates of both the Polish and the Upper Vistula River Valley populations wasλobs = 1.29. Using the deterministic population projection matrix including immigrant class, we estimated that, on average, 44 immigrants should enter the Upper Vistula River Valley population annually to match the observed growth. With survival rates increased (ΦP = 0.63,ΦB = 0.90) as to mimic no emigration and reduced dispersal, the estimated number of immigrants was only eight, indicating that substantial emigration rates are likely. A majority of the breeding sites were recorded in man-made water bodies. Colonisation has started in the southeast and proceeded towards the northwest. The strong, stable population in western Ukraine may explain high numbers of immigrants that could originate from there. Other factors favouring quick colonisation of Poland include availability of suitable breeding sites, the wide flexibility of the species with respect to breeding habitat, plentiful food, and high breeding success in the Upper Vistula River Valley. It also seems likely that westward shifts in both breeding and wintering ranges could add to the strong population increases in Eastern Europe.
Highlights
Changes of breeding ranges coupled with population size changes are phenomena of central interest in ecology (Newton 1998)
Range expansion started in southeastern Poland, and Whiskered Terns settled in northwestern Poland just after 2001
Between 1985 and 2007, the breeding population of the Whiskered Tern in Poland increased sharply from eight pairs to approximately 1,600 in 2007, and the same growth rate was seen in the strongest Polish population in the Upper Vistula River Valley; the exponential model fits the observed growth
Summary
Changes of breeding ranges coupled with population size changes are phenomena of central interest in ecology (Newton 1998). Birds can travel long distances and choose suitable habitats for colonisation far from current breeding areas, so are potentially more prone to exhibit spectacular range expansions (van den Bosch et al 1992). An even larger number of factors influencing expansion is associated with the characteristics of a species or population: range and population size, species tolerance (or flexibility) to potentially new environmental conditions, population genetics, morphological, physiological and ethological adaptations and demography (Kharintonov and Siegel-Causey 1988; Duckworth and Badyaev 2007; Gunnarsson et al 2012)
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