Overlevingskansen van kievitenpulli op intensief gebruikt grasland

During the years of 1992-1996 research has been conducted on the chances of survival of earlyborn pulli of the Lapwing. The area of research was an 80 hectare area of grassland, north of Roodkerk in Friesland (the northern province of The Netherlands), intensively used by four dairy-farms. In The Netherlands, and especially in Friesland, the sport of gathering the eggs of the Lapwing is exercised strongly and allowed until april 8th. In the area of research this sport was prohibited. The aim was to obtain information on the growth of earlyborn pulli compared to laterborn pulli, in the light of the fact that in many areas in The Netherlands – in contrast with the research area – the early birth of Lapwings is usually prevented because the early eggs are then gathered. The research consisted of ringing the young Lapwings with colored rings (n = 612/213 nests), right after birth and following them until they were able to fly. The early birds, born before may 10th, were ringed with a yellow ring (n = 438/150), later born birds with a blue ring (n = 174/63). Both groups were ringed with an aluminium ring with a unique set of numbers as well. The main result was that the chances of survival of the earlyborn pulli appear to be considerably larger (21 versus 9 percent) than the chances of survival of the later born ones, and that more pulli per nest grow up (2 versus 1 per nest). The cause of this distiction seems to be the better microclimate in the early period, with taller grass providing better protection against the weather and better supply of food. The later born birds had to grow up on shortly mowed grass without adequate protection and more hindrance of agricultural activities. On average the later born pulli needed seven days more time to become able to fly, meaning that they were exposed to predation during a longer period of time. Furthermore, the earlyborn Lapwings appeared to return to their native area to breed in the second calendar year. Of the laterborn Lapwings this was not determined.