Ardea
Official journal of the Netherlands Ornithologists' Union

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Voous K.H. (1962) De Kievitensterfte in de droge zomer van 1959. ARDEA 50 (3-4): 147-161
Lapwing mortality during the dry summer of 1959. 1. The summer of 1959 was characterized by an almost rainless period with high evaporation, which was unusually long and lasted from about the middle of May to the middle of October. Throughout the country the grasslands were extremely dry and looked as if they had burnt over. 2. Particularly from the late summer months onwards the behaviour of Lapwings was different from that observed in other years. The birds did not flock together; solitary birds frequently appeared on roadsides, on lawns and in public gardens in villages and in towns. 3. During the course of the summer records of conspicuously indolent Lapwings were more and more frequent; in addition dead birds were found in growing numbers both in the field and on the roads. 4. Post-mortem examinations were made of a total of 56 specimens found dead in the period of 7-23 October 1959. The material included 36 roadvictims. 5. Composition as to sex and age of the material examined was remarkable; the relative numbers of birds of over one year of age (87%) and of males (70%) were higher than in other years (viz. 60-49% and 59%, respectively). Generally the number of Lapwings which were summering and having a moulting pause in the Netherlands was small and the composition of the summer population was abnormal. 6. Body-weights of the specimens examined were small and far below the values known from other years. The birds were in a very poor and some of them even in emaciated condition. The weight of 37 males varied from 120 to 259, average 177 gram, that of 15 females from 104 to 242, average 171 gram. According to Klomp (1947) the normal average weight of Lapwings in October is 225-230 gram in males and 224-227 gram in females. 7. The stomach of all specimens obtained as road-victims contained at least some food, but in 45% of the cases the contents were few and consisted of one or two chitinous insect remains only. The assumption of food scarcity was corroborated. 8. The variety of food found in the stomachs was great. Insects appeared in all cases; in a few instances spiders and once fresh water snails predominated. Earthworms (identified by their chitinous chaetae), which otherwise form an important food item, were conspicuous by their total absence. Instead, noctuid caterpillars (52% of cases), earwigs (42%), and spiders (60%) were most frequently found in the stomachs. Noctuid caterpillars and earwigs are active at night, whereas the spiders were mostly of diurnal types (lycosids). During the summer of 1959 earwigs were extremely numerous throughout the country. 9. No direct explanation for the concentration of Lapwings on and along roads could be given. 10. Intestinal parasites (cestodes, trematodes, nematodes) were found in 68% of 44 specimens examined. Both first-year birds (80%) and older birds (65%) were infested. Birds with large numbers of parasites showed a smaller average body weight (164 gram) than those with none or a smaller number of parasites (181 and 175 gram, respectively). 11. Intestinal bacteria were found in 12% of 33 specimens examined. Three instances of infestation with Salmonella ryphi-murium were found. 12. Insecticides could be excluded as a main mortality cause. 13. Summarizing it can be stated that during the dry summer of 1959 the Lapwings in the Netherlands showed abnormal situations in (1) size of summer population (small numbers), (2) composition of population according to age and sex (birds of more than one year of age and males predominating), (3) social and feeding behaviour (no flocking together, abnormal feeding places), (4) physical condition (mostly very poor), (5) composition of food (no earthworms, large numbers of earwigs and spiders). All of these abnormal conditions seem to have been correlated with a severe shortage of food, which in its turn must have been the direct result of the adverse weather (drought). No exact data as to the amount of the mortality could be collected. No epidemic illness seems to have played a role.


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