The food of adult partridges, Perdix perdix and Alectoris rufa, in Great Britain.

Abstract

The work on which this paper is based forms part of a research into the ecology of game birds carried on by the Bureau of Animal Population. This research has been made possible by a grant from Imperial Chemical Industries and by the donations of landowners and others interested in game preservation. Our thanks are due not only to those who have helped financially but to shooting men and keepers in all parts of the country who give facilities for this work on their estates and send us birds for examination.

The sorting out and identification of most of the seeds and other plant food was done by E. Arthurs of the Oxford Botanical Department, while the identification and volumetric measurements of insects were carried out by John Ford and E. W. Aubrooke in the Hope Department of Entomology at Oxford. We are greatly indebted to them for this assistance.

The present paper deals only with the food of adult wild partridges. Material collected from young partridges is being analysed and the results will be published later. Young birds are classed as " adults " when killed any time after the opening of the shooting season, September 1st, but a record has been kept of whether the birds examined were young adults or old birds (over 16 months old) except when crops were sent in separately by keepers and others without data. Altogether, 429 adult grey partridges (Perdix perdix) and 29 red-legged partridges (Alectoris rufa) have been examined for food. The crop contents only have been used for this purpose as food found in the gizzard is usually in such a finely divided state as to be almost unrecognizable and certainly of no value for quantitative work. There is no reason to doubt that the crop contents alone form a truly representative sample of the food eaten. As there is no evidence to suggest that some food items pass more quickly than others from the crop to the gizzard, it may safely be assumed that the material found in the crop of a partridge at death (most of the birds were shot or killed accidentally) is the food taken a short time before.

Most of the crops were taken from shot partridges and, as the shooting season is from September 1st to January 31st, the numbers examined from September to January are much greater than for other months; outside the shooting season we have had to rely on birds killed accidentally, for instance by telephone wires and grass cutters or by disease (although most diseased birds have nothing in their crops at death). Crops have been collected during the years 1933-7 and for the purposes of showing seasonal differences throughout the year the data have been combined, as in Fig. 1.

The contents of each crop were stored in tubes of 10% formalin to be sorted and examined later. The routine for sorting and identification of the various items was as follows. The whole crop contents from formalin were washed, spread out on blotting-paper and placed on a warm stage until the excess water had evaporated, leaving any green leaves at approximately the same dryness as when fresh. The green leaves, flowers and roots were then sorted out from seeds, etc., and measured volumetrically in a small measuring cylinder by displacement of water; by this means it was possible to measure the volume of any quantity greater than 0.05 c.c., but any volumes less than 0.05 c.c. were given the conventional figure of 0.025 c.c. At this stage any insects in the crop were removed and put into 70% alcohol to be dealt with later. The rest of the material (seeds) was dried further until it was possible to sort out the individual seeds. The seeds of each species were then sorted and counted, some being identified at once and others kept in a dry state for further examination.

All the data for each partridge and its crop contents are recorded on cards and the original material preserved in the Bureau of Animal Population.

The figures for volume and weight of seeds were obtained after most of the crops had been sorted, by measuring and weighing a convenient quantity (0.5-5 c.c. according to the size of seed) and counting the number of seeds in the measured sample. By this means we were able to calculate the volume or weight of very small quantities of seeds which would have been very difficult to measure directly for each crop.