Voorkomen van Stadsduiven in de stad Groningen

This paper summarizes various counts of Feral Pigeons Columba livia conducted in the city of Groningen (53°13’N; 06°33’E), The Netherlands, in 1993-2014. In 1993 a survey of all species of breeding birds in the city of Groningen yielded a total of 1099 breeding pairs (0 to 2460, 95% CI). Details of this standardized survey (mapping breeding territories in 19 study plots spread over the entire built-up area of the city) are presented in table 1, broken down by the different parts of the city (‘wijktype’). Listed are densities (‘dichtheid’) per hectare, counted numbers of breeding pairs (‘aantal geteld’), calculated number of breeding pairs (‘aantal berekend’), size of the study plots (‘opp. proefvlakken’) and total surface of each part of the city (‘opp. totaal’). Highest densities were found in the inner city, with up to 4.4 breeding pairs per hectare in a study plot of 5.7 ha. Figure 1 presents results of counts of breeding pairs in a study plot of 13.2 ha in 1993-2000. Table 2 presents results of counts of flocks in the entire built up area of the city of Groningen in November 2005, in February/ March 2008 and in November/December 2009. The results are broken down by the inner city (‘binnenstad’) and the outskirts (‘buitenwijken’). A rough indication of an estimated total (‘schattingen’) is presented as well. Table 3 lists all locations with at least 50 Feral Pigeons during at least one of the counts in 2005-2009 (maximum per counting period is listed, locations in the inner city are bold). Table 4 lists all locations with at least 10 Feral Pigeons during incidental counts between 1 January 2013 and 30 June 2014 (maximum number is listed). It is estimated that the total number in this period was ca 750. Most likely a strong increase in providing supplemental food is the main reason for the increase in numbers between 1993 and 2005. A ban on largescale feeding by the local authorities was implemented in mid-2008. This ban is the most likely explanation for the strong decrease in numbers since 2005. A check on the presence of ringed birds in 2014 revealed that almost all individuals were unringed. Details on records of ringed individuals (almost always racing pigeons) are presented in table 5. Most records are sightings (‘aflezing’) of birds where the ring number could be read in the field. The addresses of the owners of racing pigeons (‘woonplaats eigenaar’) reveal that nearly all owners lived outside the province of Groningen, underlining that their racing pigeons had lost their way. Four ringed pigeons were seen on several dates in 2014, invariably at the site where they had been observed for the first time. The site fidelity of these ringed birds is another indication that counts of flocks are a reliable alternative for a breeding bird survey.