No abstract

In an aviary experiment with captive Goldfinches (Carduelis carduelis L.) vigilance and foraging behaviour were recorded before and after the appearance of a predator. When foraging, individual Goldfinches had a low head jerk rate during the first minute, but each scan was of relatively expanded duration; the scanning rate increased with a shorter duration of each scan up to the time the predator, a Merlin (Falco columbarius), appeared. Thereafter the birds showed a low head jerk rate, which returned to the former level after ten minutes. The time spent feeding was low if head jerk rate was low and high if head jerk rate was high. There were significantly more scans of long duration after the predator was visible compared with undisturbed feeding. The intake loss of individuals due to increased vigilance after the appearance of the predator during the following minutes is calculated to be 53%. A linear, negative regression function is formulated relating the number of scans per time unit and total time spent scanning: [Formula: see text] With increased number of scans the total time spent vigilant is decreased. From this is concluded that if birds ingest relatively large sized seeds and therefore only a few per time unit they gain a higher security against predators compared to feeding on small sized seeds and ingesting relatively more, because time not spent vigilant is increased with increased pecking rate.

The effect of bio-dynamic and conventional (= intense) agriculture management on the structure of the spider fauna in cereal fields and on the activity densities of dominant Erigoninae and Lycosidae species was compared in a 4-years-study in the Niederrheinische Bucht, F. R. G. The percentage of the two species most commonly sampled (Oedothorux upicutus and Erigone utru, both Erigoninae) was 66 % on bio-dynamic and 81 % on conventional fields. Their activity densities on conventional fields were usually higher than on the corresponding bio-dynamic fields. In contrast, all other spiders were more common on bio-dynamic fields. 11 % of the spiders sampled on biodynamic fields were Lycosidae; on conventional fields, species of this family became almost extinct (2 Yo). The dominant Lycosidae was Purdosu amentutu. Most s ecies of Lycosidae were largely restricted to the field-edges, only Purdosu prutivuga invaded the fielblcenters in higher numbers. It is concluded that the occurence of Lycosidae in arable land depends on agricultural management as well as on the presence of nearby undisturbed areas.From the results it might be concluded that the potential rey impact of spiders on Aphidina and Collembola is not reduced on conventional fields comparecfwith bio-dynamic fields, but the prey impact on somewhat larger insects must be extremely low. For conservating a diverse spider fauna on arable land, it is necessary to reduce the application of pesticides and to support the colonisation of spiders into cereal fields. To it the size of the fields should be rather low and the fields intermixed with undisturbed areas.

No abstract

The food of a population of Europeans Goldfinches breeding in Orchards was studied. More than 5% of the total foodstuff consumed was met by the seeds of seven food plants. Water, lipid, carbohydrate and protein content was determined from 20 different plants which Goldfinches used during the breeding season in order to calculate energy content. The energy of fresh seeds varied from 1.88 kJ/g in Tussilago farfara to 12.14 kJ/g in Dactylis glomerata. The dependence of the rate of energy intake (profitability) on the pecking rate and the size (weight) of the seeds was calculated. The profitability of various seeds is in agreement with the relative number of birds using them. Calculation of the feeding time that a Goldfinch needs during daylight hours, if it feeds only on a particular plant, indicates that there are several foods that cannot fill the energy demands of the bird during the breeding season. These are eaten only if others with a high energy content are not available. Thus food selection in Goldfinches depends, apart from availability, on seed profitability. The oxygen consumption of a male Goldfinch was significantly higher when the animal was feeding on seed heads of Tussilago farfara and Taraxacum officinale than when it fed on loose dry seeds, and so, different feeding techniques have to be taken into account in calculating net energy gain.