DOI: 10.5061/dryad.j3tg5
title: Data from: Non-breeding range size predicts the magnitude of population trends in trans-Saharan migratory passerine birds

description: Understanding why populations of some migratory species show a directional
 change over time, i.e. increase or decrease, while others do not, remains
 a challenge for ecological research. One possible explanation is that
 species with smaller non-breeding ranges may have more pronounced
 directional population trends, and their populations are thus more
 sensitive to the variation in environmental conditions in their
 non-breeding quarters. According to the serial residency hypothesis, this
 sensitivity should lead to higher magnitudes (i.e. absolute values) of
 population trends for species with smaller non-breeding ranges, with the
 direction of trend being either positive or negative depending on the
 nature of the environmental change. We tested this hypothesis using
 population trends over 2001–2012 for 36 sub-Saharan migratory passerine
 birds breeding in Europe. Namely, we related the magnitude of the
 species' population trends to the size of their sub-Saharan
 non-breeding grounds, whilst controlling for factors including number of
 migration routes, non-breeding habitat niche and wetness, breeding habitat
 type and life-history strategy. The magnitude of species’ population
 trends grew with decreasing absolute size of sub-Saharan non-breeding
 ranges, and this result remained significant when non-breeding range size
 was expressed relative to the size of the breeding range. After repeating
 the analysis with the trend direction, the relationship with the
 non-breeding range size disappeared, indicating that both population
 decreases and increases are frequent amongst species with small
 non-breeding range sizes. Therefore, species with small non-breeding
 ranges are at a higher risk of population decline due to adverse factors
 such as habitat loss or climatic extremes, but their populations are also
 more likely to increase when suitable conditions appear. As non-breeding
 ranges may originate from stochasticity of non-breeding site selection in
 naive birds (‘serial-residency’ hypothesis), it is crucial to maintain a
 network of stable and resilient habitats over large areas of birds’
 non-breeding quarters.
description: Magnitude and direction
 of population trends, ecological and life-history traits of 36 passerine
 species breeding in Europe between 2001 and 2012Magnitude and direction
 of population trends (1 = 100%), ecological and life-history traits of 36
 passerine species breeding in Europe between 2001 and 2012. Non-breeding
 niche position varies from 1 (closed forest) to 7 (open country) and
 non-breeding niche breadth expresses the difference between the values of
 the two main habitats; non-breeding habitat wetness scores from (1) dry to
 (3) aquatic habitats. Non-breeding regions: (1) west–central region, (2)
 west–east region, (3) central–south region, (4) ‘entire’ region. Breeding
 habitat: forest (F), wetland (W), urban (U) and open habitat (O). PC 1
 expresses a gradient from ‘slower strategy’ (K-selected) species to
 ‘faster strategy’ (r-selected) species. PC 2 depicts a gradient from
 species allocating most of their energy to just one breeding attempt per
 season to species spreading their investments across multiple breeding
 attempts per season.Kolecek_et_al_Oikos_data.xls