Source-Sink Relationship in a Metapopulation of Suburban and Rural House Sparrow Populations

In the last part of the twentieth century the House Sparrow Passer domesticus population started to decline in The Netherlands. To investigate whether there is a difference in yearly growth factor between urban and rural areas we estimated for two local House Sparrow populations, one suburban (in Leek) and one rural population (in Terheijl), the life history parameters, reproduction and survival. The mean (± SE) number of broods per year was (Leek vs. Terheijl): 1.202 ± 0.039 and 1.463 ± 0.043 and the mean number of fledglings per adult per brood 1.294 ± 0.033 and 1.744 ± 0.033. The analysis of survival data was performed with half-year-periods resulting in yearly survival estimates of juveniles of 0.325 and 0.395 and of adults of 0.442 and 0.487, for Leek and Terheijl, respectively. Based on these life history values a matrix population model for these populations was developed. Due to the different population growth factors of the two populations, we developed a metapopulation model in which we included a dispersal flow of juveniles from the (thriving) rural population to the surrounding environment, i.e. partly to sub-urban Leek. A simplified version was fitted to long term population estimates in Leek and Terheijl. This resulted in a dispersal of 48.5% of the juveniles from Terheijl. From this percentage leaving Terheijl only 19% should reach the population in Leek. These estimates resulted in a yearly growth of the metapopulation of 0.6% and thus the seemingly stable population numbers that are observed in Leek and Terheijl. More insights into this local source-sink relationship could help create awareness of the dependence of seemingly viable House Sparrow populations in (sub)urban areas on dispersal of juveniles from rural areas.