Three related questions were studied:
To study the first question I received help of 42 volunteers, who counted House Sparrows around their house in a standardised way: counting periods of 30-45 minutes after supplying food at a fixed time and place on the ground each day for 14 days in spring and autumn. The results of a first group of 18 participants were corroborated by a second group of 24 participants one year later, revealing that House Sparrows were almost extinct in residential areas of the larger urban settlements in the Gooi & Vecht region (the Netherlands) where most houses were built before 1953, whereas (contrary to the believe of many experts) in more recently built districts House Sparrow populations were still thriving.
The second question was studied with the help of 18 participants of the Garden Bird Survey, a scheme run by SOVON. I selected the participants on the basis of having provided a full year of weekly counts of the birds in their own gardens. Their data showed a similar dichotomy of sparrow-poor and sparrow-rich gardens and, most importantly, that Magpies were regular visitors in equal numbers to both types of gardens. It therefore seems extremely unlikely that Magpies were responsible for low numbers of birds in sparrow-poor areas.
To answer the third question it was hypothesised that
Created on ... July 10, 2000