De broedbiologie van de Tortelduif Streptopelia turtur

The breeding biology of Turtle Doves was studied during 1977-1981 in woodland in the central part of the Netherlands. The arrival of Turtle Doves in spring on the breeding grounds was not correlated with the warmth sum (in °C) for April. On 19.732 ha 794 territories were found, using the mapping method (4,0 p/100 ha). Highest densities were found in woodland and garden-cities, intermediate densities in built-up areas and mixed farmland and low densities in forelands, heatherland and open farmland (figure 1, table 1). Numbers declined during 1969-85 in two plots of 147 and 350 ha respectively (figure 3). The cause of decline was habitat destruction in one of these. Start of laying, as expressed in figure 4 for 1977-81, fluctuated from year to year. Two peaks in laying were found in four out of five years, indicating the production of two broods per pair per year. Start of laying seemed to be influenced by the timing of arrival (measured as the median date of the first ten arrivals) and the warmth sum (in °C) for May (figure 5a, 5b), but not with the number of hours with sunshine during May (figure 5c) and precipitation in mm during May (figure sd). Clutch size was either one (n = 11) or two eggs (n = 132). C/1 was evenly distributed over the entire breeding season. Eleven C/1 resulted in 7 hatched eggs and 7 fledglings (63,6%), whereas 132 C/ 2 resulted in 148 hatched eggs and 120 fledglings (45,5%). Overall breeding success was 46,2%. Clutches started at the end of June and early July were most succesful (table 2). Variation in breeding success from one year to another (table 3) was largely due to weather: cold, wet seasons resulted in poor breeding success. Among 68 losses, 24 were due to predation, 8 to disturbances with desertion as a result, 3 to dropping of the eggs and in 33 cases the cause of nest failure was unknown. Partial losses among C/2 occurred six times during the egg stage (4x infertile, 2x dropping) and two times during the nestling stage (1x certain and 1x possible dropping). Feeding mostly occurred within the forest boundaries, usually within the near vicinity of the nest but sometimes farther away. Foraging on nearby farmland was hardly ever observed (unlike in Woodpigeons). The seeds of Scots pine, larch, spruce and fir constituted the main diet during summer. In late summer, most birds foraged on the seeds of Corydalis claviculata, Deschampsia flexuosa, Rumex acetosella, Spergula vernalis, Cruciferae and Stellaria media. Once feeding on larvae of Coccinellidae was observed.