Notes on Marsh Harriers

SOME NOTES ON MARSH HARRIERS T h e status of the Marsh Harrier (Circus aeruginosus) as a breeding bird in this country is precarious, and is likely to remain so as there seems no likelihood of suitable habitats—large reed beds— increasing in n u m b e r . T h e tendency is in fact the other way, and if drainage for agricultural purposes is permitted on, say, half a dozen more marshes in East Anglia, there will be no more nests. Every site is well worth fighting for.

T h e Marsh Harrier is remarkable for variety of plumage and of behaviour. A bigger, clumsier bird than M o n t a g u ' s Harrier or the H e n Harrier, it is more like a Buzzard in general appearance.

It flies more slowly as a rule than other Harriers, having broader wings and a slower wing-beat. But one must not be deceived about the bird's capabilities by its normal rather heavy flight.

I have seen a lazily soaring bird dive at a Carrion Crow with a speed reminiscent of that of a Peregrine, because the crow flew over the nest containing young. And the breeding male at times gives an aerial display which is astonishing. I t is usual in the spring to r.ee the male soaring in circles over the nesting site.

H e m o u n t s effortlessly with few wing beats if conditions permit, often reaching a height where it is necessary to keep one's glasses on him or lose him altogether. After a time he begins dipping or rising again, the dives becoming steeper and longer as his excitement mounts. Sometimes he then comes right d o w n in three or four steps, and circles the marsh or goes to ground.

But if one is patient one sometimes sees a descent f r o m a great height in a vertical line, wings flexed and head down ; about halfway down he may loop the loop or spin and t u m b l e ; finally diving headlong until, only a few feet f r o m the reed tops, he pulls out and rises steeply on broad, rigid wings. T h e whole Performance takes b u t a few seconds, though he may previously have soared for so long, perhaps half an hour, that one has given u p watching because of aching arms and neck. And of course the display is often not particularly thrilling; but I can still remember two displays I saw in 1948 from the same cock, a bigamous bird who displayed impartially over two nest sites several miles apart. Some of the evolutions performed, apparently u n d e r stress of great emotion, show an astonishing mastery: the bird at times apparently quite out of control, tumbling and twisting almost as if shot, but regaining poise with startling rapidity.

Variety of plumage is so marked that in many cases one is able to identify an individual quite easily and follow its fortunes t h r o u g h a whole season. T h u s I was in no doubt that the 1948 cock had two mates. I saw him give a tremendous display over one site on M a y 9th and over the second site on May 19th.

After M a y 29th, though I watched the first site regularly, I did not see h i m

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HARRIERS

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there at all. He may, of course, have visited this site when I was not there ; but certainly the female did a great deal of hunting for herseif and her family, and finally only one young bird flew from that nest on July 18th. Two flew from the second nest, though they were late, being still in the nest with much white down still adhering to their plumage on August 4th. The apparently deserted female was constantly observed off the nest for long periods on warm days, often over an hour at a Stretch ; sometimes during a watch of two or two and a half hours she would make a few short Visits totalling perhaps ten minutes. On these visits she often carried dead reeds to the nest, a curious habit often seen in harriers, but in this case one would have thought rather a waste of effort. T h e last reed carrying I saw was on June 19th, and after that I hardly ever saw the bird go near the nest. In fact, I had concluded that something had happened to prevent success, but on July 6th, when I was up a tree watching some spooonbills I saw her carrying prey to the nest. T h e one young flew on July 18th. Like all young Marsh Harriers it was rieh chocolate brown ; and the head, dark with a buff patch at the nape, was perhaps typical, though many young have buff crowns like adult females.

In 1950 three young from one nest all had buff crowns, though two were somewhat streaked. I have also seen well-grown young with no buff on the head at all.

Plumage in fact varies remarkably. I have seen a wintering female appear very grey even at close ränge, but this was only on one occasion, in 1951. T h e chief Variation in female plumage is the extent of buff on the shoulders. Sometimes this is very extensive, and sometimes also it (and the crown as well) is more off-white than buff.

Male plumage can be very difficult. The fully mature cock, three or more years old, can look quite magnificent. At his best he has buff head (probably more streaked with dark than the female's), an almost chestnut back, black ends to the longest primaries, pale grey secondaries and tail, and very light underwing. He can thus appear in certain lights almost black, white and chestnut, utterly unlike a younger cock or any female.

But one does not often see such fine speeimens.

Young males show grey on the upper tail surface first and later on the secondaries. If the secondaries are still dark it can be almost impossible to sex a bird except by behaviour. One year I remember that, although I feit fairly certain which was which, I was not really satisfied tili one carried prey over the nest and the other rose to take the pass.

Another perplexing point is that some females show very pale at the base of the tail, almost as if they were white rumped Montagu's. A short view of a bird like this can lead to a wrong identification unless the observer notices size and flight;

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but on closer inspection it is seen that this pale patch is more diffuse and less sharply defined than a Montagu's rump.

So marked are the plumage differences that I now often note a bird as " not obviously male " instead of "adult female ", and I strongly suspect myself and others of having been overconfident in the past in some of our diagnoses.

The Marsh Harrier is with us a summer resident, but overwintering is common. In autumn half a dozen birds may occasionally be seen in one area for a while, chiefly at the end of August or in September. Some I think migrate, or make considerable weather movements, very late if theweatherbecomes severe.

In 1949, I saw a bird on Jan. 6th which I know had bred the previous season and which I had seen regularly throughout the latter months of that year. But I saw no more after Jan. 6th tili May 12th. In 1950, on the other hand, birds were seen every month, four together on Jan. 4th, one a cock, and one or two were present through January, February and March.

In fact, one expects to see the odd bird any month, and in my note books February is the month with fewest records.

The part played by the cock in the breeding routine must naturally vary considerably in a species wherebigamy occasionally occurs. But where the cock is always present, the amount of assistance he gives the female is Very variable.

The normal procedure is well-known. The female does most of the incubating, the cock most of the hunting. The latter returns with prey, circles over the nest, sometimes calling ; the female rises and takes the food from him in the air. Often the female leaves the eggs for a prolonged breather : at times she hunts for herseif. The passing of the prey also varies very much. Sometimes the cock drops it and she catches it well below him. Sometimes she flies beneath him, turns on her back and takes it from his talons with hers. I once saw a female fly very slightly below and behind her mate, Stretch out her left leg and take the prey from the male in level flight. When she has it, if it is for herseif, before hatching has taken place, she generally goes down to a place about fifty yards away from the nest to eat it. Some cocks are disappointing to watch because they merely drop the prey on this chosen feeding site, and all one sees is the female Aying to it and back to the nest a few minutes later.

Incubation, though normally done by the female, is occasionally shared by the male. At least, he at times relieves her and either incubates or mounts guard—as I normally watch from a distance, not from a hide, I cannot be sure which. If he does not go down to the nest—some cocks appear never to do so— the male often flies over the site even when not carrying prey.

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The most attentive male I ever saw, in 1952, fed the three young himself three times in thirteen minutes. That was on August Ist, a few days before the young flew, and the female was away at the time over another marsh. This same cock carried dead reeds to the nest on June 29th, again at a time when the female was away. This female was frequently off duty, and once the young flew I hardly ever saw her, though the cock was always present and often dropped prey for them.

It was in connection with this 1952 nest, that I saw a very odd occurrence.

There was always a Montagu's Harrier about over the area, a male whom we suspected of having been robbed.

The female was not seen after the early part of the season, and the male often flew down the marsh and indulged in apparently mock aerial fighting with the cock Marsh Harrier. Whichever bird was below would turn over with raised talons and I frequently saw chasing of either male by the other. After the young Marsh Harriers were on the wing, making frequent short flights within a hundred yards or so of the nest, I saw the male Montagu fly around apparently quite interested. The male Marsh Harrier chased him a short way, but he returned and went down into the Marsh Harrier's empty nest. When he rose again almost at once, he was carrying something in his talons, which he neatly dropped on the spot where I had observed a young Marsh Harrier alight. I am quite certain of the accuracy of the Observation, but hesitate to suggest any explanation.

Male Marsh Harriers will also drop prey to the young when they have flown a distance from the nest, and the female of course does the same. I believe I once saw a juvenile turn over and take prey from the female in the air, but a tree made Observation difficult at the exact moment. Certainly the female was carrying, the juvenile flew to meet her, and when they cleared the tree the female no longer had prey. The juvenile went to ground.

A few days later I saw a juvenile of this family turn over and raise its talons under the female, but this time she was not carrying.

This behaviour connected with nest and young is quite unpredicable, there being a wide ränge of possibilites. In 1953 for example, I saw a male carry prey over the nest site. After several times passing the nest he went down, but at once rose, still carrying. He then dropped the prey about twenty yards away, and a juvenile at once flew from the nest to this spot.

This variety of behaviour makes Marsh Harrier watching quite fascinating, but it is extraordinary how many hours one can watch and see nothing at all if one happens to be unlucky. There is no regularity at all about feeding times, unless in the early morning about which I cannot speak.

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When the young are fledging and for some time after they can fly, it is usually possible to find one or other of the adults, generally the female, perching somewhere at hand. Time after time I have found the same dead bough of an oak occupied by the same bird, which is ready to take off after a crow or other possible predator. At this stage I have known a male still bring food for the female. This occurred in 1956. The female ignored the cock as he flew past her oak tree perch carrying prey ; after several runs he dropped it and went down to it. The young at this time were Aying strongly.

I mentioned earlier that I usually watch from a distance. I do so because most Marsh Harrier sites are accessible to the curious and because one inevitably leaves a track through the reed bed which invites others to follow. Where the visitors can be limited by whole-time Wardens, no disturbance need result. But it is obvious that on unpatrolled marshes it is unwise to Start the ball, shall we say snowball, rolling. A fine week-end might easily spell the end of a promising nest. Also, there are still those who will try for the eggs despite the penalties under the new act. I very much hope that these notes will not send anyone out into the reed-beds. There is fine entertainment to be had from afar.

G.

B. G .

BENSON.

NOTE ON A TAPEWORM FROM A YELLOWNECKED FIELD-MOUSE B y STEPHEN

PRUDHOE

Department of Zoology, British Museum (Natural

History)

The writer has been afforded the opportunity of examining a tapeworm from a yellow-necked fieldmouse (Apodemus flavicollis) collected by Dr. Grace Griffith at Bures, Suffolk. The tapeworm appears to be an example of the species Catenotaenia lobata Baer, 1925, a form recorded hitherto from A. flavicollis only in Russia. The occurrence of C. lobata in this host in Britain is, however, not surprising, since the parasite has been collected on many occasions from the intestine of the wood-mouse (Apodemus sylvaticus) near Oxford * and more recently from the same host species in West Wales **. Moreover, the present writer has found it in the bank-vole (Clethrionomys glareolus) in Berkshire. * Baylis, H. A., 1927. Ann. Mag. Nat. Hist. (9) xix p. 434. ** James, P. M., 1954. J. Helminthol., xxviii, p. 183.