Ardea
Official journal of the Netherlands Ornithologists' Union

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Klomp H. (1951) Over de achteruitgang van de Kievit, Vanellus vanellus (L.), in Nederland en gegevens over het legmechanisme in het eiproductie-vermogen. ARDEA 39 (1-3): 143-182
The Lapwing has diminished in numbers in Holland during the last 25 years. It is often assumed that this decrease is caused by the taking of eggs, which is legally allowed until the 20th April. Results are published in the present paper of a study regarding the influence of egg-taking on the reproduction. It is shown that Lapwings which continually lose their eggs up to 20th April come to incubation after the period of egg-taking is closed. The incubation period is delayed, however, 3-4 weeks and in consequence the lapwing is brought into contact with the mechanical moving of grass. By means of an inquiry it is shown that the results of reproduction are reduced by 10% by mowing. From a series of experiments regarding the recovery capacity of the lapwing it could be calculated that 40% of the losses caused by mowing are nullified by the formation of a new clutch. Thus the amount of loss is reduced to 6.2%. It can be assumed that this loss causes but a slight decrease in numbers, which makes it necessary to look for another factor which is responsible for the large decline. In a future paper it will be shown that the decrease in numbers is caused by the improvement of the grassland as a result of the regulation of the water-level and the administration of chemical manure, and that this correlates with the habitat requirements of the bird. In connection with some problems concerning the taking of Lapwing eggs, the physiological control of clutch size and the egg-production capacity was examined. From experiments on adding and removing eggs during laying, it appeared that the Lapwing is a determinate layer (LACK 1947). It always lays a total of 4 eggs and after one or more eggs are removed during laying, the bird would have to incubate an incomplete clutch. If eggs are added during laying, the female Lapwing never ceases laying before she has produced 4 eggs. After removal of all the eggs during laying the reaction of the Lapwing varies and is dependent on the number of eggs taken. When the first egg is taken when laid the bird produces another four in succession in a new nest (the 2nd, 3rd and 4th egg plus 1 additional). When the first 2 eggs are taken when laid, the bird produces 3 or 4 eggs in succession in a new nest (the 3rd and 4th egg plus 1 or 2 additional), or in exceptional cases the bird waits after having laid the 3rd and 4th egg in a new nest and after 5-7 days produces 2 or 3 more eggs in the same nest. Sometimes the bird deserts the 3rd and 4th egg when laid and lays another clutch of 4 eggs in a new nest after a week. When 3 eggs are taken when laid, the 4th egg is laid in a new nest and normally deserted. After a week a new clutch of 4 eggs is produced. In one case the bird did not desert the 4th egg and after some days added 2 eggs in the same nest. To summarize these experiments, the lapwing is only capable of producing more than 4 eggs in succession when she recommences laying in a new nest. Suppressing of eggs occurs possibly after 5-7 days when the bird adds some eggs of a new clutch to the remnant of a clutch that has been partly taken. In this latter case the resulting clutch may be composed as follows: 2 + 2, 2 + 3 and 1 + 2 eggs (see Appendix II, females 61, 63, 64 and 70). The Lapwing breeds but once; after rearing the young no second brood is made. When the clutch is taken just after laying, the bird produces a new one within an average of 12 days. When this second clutch is also removed, the bird recovers itself again and produces a third clutch, and so on. When egg-laying is started early in the season (the end of March or the beginning of April) the Lapwing is able to produce 5 clutches when the eggs are removed every time shortly after the 4th egg has been laid. Egg-laying ceases at the end of Mayor in the first decade of June, when moult sets in. The production of a further clutch is determined primarily by the time of the year; the number of eggs already laid and the length of the incubation period play only an unimportant part. But the number of clutches that can be produced may be influenced by the duration of incubation, for the time required for producing a clutch may be elapsed by brooding. Even after the loss of the chicks a new clutch can be produced provided that the season is not yet too far advanced (see Fig. 1 and Appendix III). From the foregoing it is obvious that the Lapwing possesses great powers of recovery. From a point of view of natural control this recuperation is of interest by reason of its stabilizing influence on reproduction.


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