Data from: Multiple components of environmental change drive populations of breeding waders in seminatural grasslands

Environments are rapidly changing due to climate change, land-use, intensive agriculture and the impact of hunting on predator populations. Here we analysed long-term data recorded during 1928-2014 on the size of breeding populations of waders at two large nature reserves in Denmark, Vejlerne and Tipperne, to determine the effects of components of environmental change on breeding populations of waders. Waders are closely associated with coastal marshes and meadows, and such habitats have been reduced extensively during the last century with negative impacts on population trends of waterbirds. Environmental variables and counts of waders were temporally autocorrelated, and hence we used Generalized Least Square (GLS) by incorporating the first order autoregressive correlation structure in the analyses. We attempted to predict the abundance of waders for short-term trends for two nature reserves (35 years) and for long-term trends for one nature reserve (86 years), using precipitation, temperature, nutrients, abundance of foxes Vulpes vulpes, area grazed and number of cattle all standardized to a mean = 0 and SD = 1). There was evidence of impacts of nutrients, climate (long-term changes in temperature and precipitation), grazing, mowing and predation on bird populations. We used standard random effects meta-analyses weighted by (N – 3) to quantify these mean effects. There was no significant difference in effect size among species, while mean effect size differed consistently among environmental factors, and the interaction between effect size for species and environmental factors was also significant. Thus, environmental factors affected the different species differently. Mean effect size was the largest at +0.20 for rain, +0.11 for temperature, -0.09 for fox abundance and -0.03 for number of cattle, while there was no significant mean effect for fertilizer, area grazed and year. The negative impact of number of cattle on abundance of waders implied that a management tool actually had a significant negative impact on the population. Effect sizes for two short-term time series from Tipperne and Vejlerne were positively correlated as were effect sizes for short-term and long-term time series at Tipperne. This implies that environmental factors had consistent effects across large temporal and spatial scales