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THE FOOD OF NESTLING PURPLE HERONS IN HOLLAND By D. F. OWEN and G. C. PHILLIPS FEEDING HABITS AND AREAS STUDIED IN late June 1956 we visited two colonies of Purple Herons (Ardea purpurea) in Holland in order to observe feeding and other behaviour for comparison with our studies in England of the Common Heron (A. cinerea). The colonies visited were at the Naardermeer reserve (10 miles S1E, of Amsterdam) and at Nieuwkoop (15 miles S.W. of the Naardermeer). At the Naardermeer we were told that there were over 150 pairs >f Purple Herons nesting in 1956 and at Nieuwkoop at least 200 pairs, where they bred for the first time as recently as 1946. We spent a week watching the adult birds feeding, and in addition, collected 56 food-samples from the young at the Naardermeer and 17 from those at Nieuwkoop. All food-samples were collected in the last week of June, and thus the results given in this paper refer only to that period. There can be little doubt that the food of the nestlings varies with the time of year and also from year to year. This paper describes what we found in the food-samples and includes a few notes on the behaviour of nestlings and adults. The Naardermeer consists of a series of lakes connected together by waterways and surrounded by extensive reed-beds (mostly Phragmites sp.) and fen scrub chiefly alder, birch and sallow. There were two groups of nesting Purple Herons, the main one in a Phragmites marsh, and a small one of 30 pairs (the group we studied) in sallow bushes at the edge of an area of fen scrub. All the nests in this latter group were less than 10 feet and most were only 3-5 feet above the ground. At the Naardermeer many adult Purple Herons were seen hunting for food along the numerous narrow canals and in pools surrounded by reeds. Others were seen hunting along the edges of ditches outside the reserve, but our observations did not suggest that the birds regularly travelled more than a few miles from the heronry for food. In many respects Nieuwkoop is similar to the Naardermeer, but it is larger, and much of it is open to the public (unlike the Naardemeer). Here the Purple Herons nest in an alder wood, though considerable numbers also nest in sallows near-by. The alders varied in height from 6 to 20 feet. At Nieuwkoop many of the adult Purple Herons seemed to fly considerable distances for food, but we do not know to what type of habitat. In addition, many birds were also seen feeding in the canals and among the reeds, just as at the Naardermeer. At this colony a few pairs of Common Herons nest with the Purple Herons, and Little Bitterns (Ixobrychas minutus) and Bitterns (Botaurus stellaris) are evidently quite common in the area. At the Naardermeer the only 494 VOL. XLIX] FOOD OF PURPLE HERONS 495 other breeding heron is the Bittern, but numbers of Common Herons visit the Cormorant (Phalaerocorax carbo) colony where they scavenge regurgitated food. In Holland all our observations of adult Purple Herons suggested that they fed singly, though often several individuals could be seen in quite a small area. They seemed to feed closer together than Common Herons in England, but this might be due to the greater concentration of breeding pairs in the area and the rich feeding-grounds. In the Camargue, one of us (D.F.O.) has watched Purple Herons feeding and here also they were always solitary, quite unlike the Little Egrets (Egretta garsetta) and Night Herons (Nycticorax nycticorax) which are distinctly social. METHODS OF OBTAINING FOOD SAMPLES AND THE BEHAVIOUR OF NESTLINGS WHEN ALARMED Young Purple Herons, like many other fish-eating birds, readily regurgitate food when alarmed, and this is a useful means of studying the food of such species—see Van Dobben (1952) for the Cormorant, and Owen (1955) for the Common Heron. Probably the birds regurgitate to scare or to divert the attention of their enemies, and, possibly, once relieved of food they are able to escape from the nest more easily. Using this method of obtaining food-samples it is not easy to get food from nestlings less than 10 days old, but some samples were collected from small young by gently massaging the stomach region soon after they had been fed. All the items of prey found in the food-samples were identified on the spot and left in the nest where they were eaten again by the nestlings. Samples were collected from about 50 different nests, some nests being visited more than once. At the Naardermeer all the samples were collected in the early morning and in the evening, at which times there appeared to be a peak of feeding- activity (as in the Common Heron in England). We found that young Purple Herons regurgitated more readily than Common Herons, and rarely attacked the observer, unlike Common Herons which normally attack. There was also a greater tendency to leave the nest and plunge into the undergrowth: even quite small young of about two weeks old would leave the nest when alarmed. Hanzak (1949-50) reported that in Czechoslovakia young Purple Herons 8-10 days old readily left the nest when alarmed and returned later. Related to these differences of behav­ iour between the two species of heron, it might be mentioned that the nest of the Common Heron is considerably enlarged and made more cup-shaped' during the incubation-period and when the young are still small. When the eggs are laid the nest is flat, but by the time they hatch it is distinctly cup-shaped. This seems to serve the function of keeping small young in the nest. We found that the nests of the Purple Heron were much smaller than those of the Common Heron and there was hardly any sign that the nest had been built up during incubation. This is probably related 496 BRITISH BIRDS [VOL. XLIX to the fact that the young Purple Herons leave the nest when disturbed and any building up of the nest might tend to prevent them from doing this as efficiently as they do. SIZE OF PREY We estimated by eye the length of most of the fish found in samples and found that, like the Common Heron, the Purple Heron catches fish selectively, fish of 110-200 mm. (ca. 4-8 inches) in length being much more numerous than either smaller or larger individuals. The size of fish taken by the Purple Heron in Holland was very similar to that taken by the Common Heron in England (Owen, 1955). This is of particular interest as smaller fish must have been more numerous than larger fish of the same species. All eels taken were larger than 150 mm. (6 inches) and smaller than 400 mm. (16 inches)., suggesting that these fish were also being taken selectively. We could find no evidence of adult Purple Herons bringing smaller prey for the small young. Once, at Nieuwkoop, we found a pike 350 mm. (14 inches) long and' a rudd 240 mm. (gf inches) long in the bottom of a nest containing three young about two weeks old. Obviously these fish were much too large for the young birds to swallow and they had been rejected. Adult Common Herons almost always partly digest a large fish before giving it in pieces to small young, and presumably this normally happens in the Purple Heron. As the prey found in the food samples varied considerably in size TABLE I—LARGE PREY IN FOOD-SAMPLES PROM NESTLING PURPLE HERONS (Ardea purpurea) IN HOLLAND, JUNE 1956 Naardermeer Nieuwkoop (56 samples) (17 samples) Pike (Esox lucius) 12 3 Carp (Cyprinus carpio) 1 Gudgeon (Gobio gohio) _ 2 Tench (Tinea tinea) 7 2 Rudd (Scardinius erythrophthalmu.i)* 42 16 Bream (Abramis bra-ma) 9 — Eel (Anguilla anguilla) 9 1 Perch (Perca fluviatilis) 10 13 Ruffe (Acerina cernua) — 2 Burbot (Lota vulgaris) 2 _ Water Vole (Arvicola amphibius) (adults) 14 7 (young) 28 1 Mole (Talpa europaea) 10 1 Shrew (Sorex sp.) — 1 Frog (Rana sp., mostly temporaria)* 8 2 Skylark (Alauda arvensis) (young) 1 TOTAL 'S3 Si *Note: " Rudd" may also include Roach (Rutilus rutilus), and a few of the frogs may have been Rana esculenta. VOL. XLIX] FOOD OF PURPLE HERONS 497 it would be misleading to compare directly the numbers of each species without making- some allowance for size. This difficulty has been partly overcome by dividing the prey into two categories : Large prey. All eels more than 150 mm. (6 inches) long, all other fish more than 100 mm. (4 inches) long and all mammals and birds. Within this category there was some variation in size, but it is not so great as to give misleading results. Small prey. This includes all fish smaller than the above and all insects, but very few small prey were found in the food samples collected from the nestling Purple Herons. SPECIES TAKEN Most species of prey found in the food-samples were easily recognisable in the field, the greatest difficulty being experienced with the closely related rudd and roach. All fish in good condition which might have been either of these species were found on close examination to be rudd, and it therefore seems likely that most were of this species. Naardermeer. Table I shows the large prey found in the food-samples collected at the Naardermeer. A total of 153 items of prey were identified, almost entirely fish and mammals.

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