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COYPU ( M Y O C A S T O R

COYPUS)

AT MINSMERE BIRD RESERVE by

H.

E . AXELL

ROYAL SOCIETY FOR THE PROTECTION OF BIRDS

THE marsh land of this R.S.P.B, reserve Covers some 395 acres. Much of it is new reed swarrip, developed from the deliberate flooding of 1940-45 (Trist, 1952) and affected again by the sea break-through of 1953. There are 18 shallow freshwater meres, mainly stagnant and mostly small ; the largest is now only of six acres and each area of open water has been steadily shrinking with the spread of reed (Pliragmites communis). A few acres of higher ground are covered with a mat of rough grass with some scattered scrub. There is a widespread ditch network. Reed cutting, mainly in front of Observation hides, is done on a comparatively small scale. After their original escape from near Norwich in 1937 and subsequent increase and spread, (Ellis 1960), coypu were first noticed at Minsmere in 1955. Colonisation of this eminently suitable habitat was slow and by late February, 1959, when the writer began work at Minsmere, evidence of them was still very little. However, by July of that fine warm summer, seven groups of young averaging three months old, were known and there were probably as many again in a large area kept strictly undisturbed during the breeding season of the marsh harriers (Circus aeruginosus). Destruction of reed at this time was negligible, some edges being trimmed at the border with open water, but stronger attacks were made on clumps of sea clubrush (Scirpus maritimus) and sedges (Corex spp.). No significant increase was noticed until the spring of 1960 when about double the number of adults and small young were to be seen in the same areas as in 1959. But still by far the greater part of the marsh remained unpenetrated by coypus, habitat destruction and population increase being so small as apparently to require only a minor spread of territory. Evidence of changes in the numbers and location is obtained more from sign than by sight of the animals. Paths on low embankments through the marsh are machine-cut and thus are mainly of short grass. It is on these narrow strips between the reeds that litters of faeces are most commonly seen also tracks emerge from the reed cover. Small, partly-built and mostly unused beds of cut plants and canopies interwoven about a foot high occur in reeds close to an open area of fairly dry ground ; these also indicate new areas of activity. These clumps of ' buildings ' are few and appear mainly in late autumn. Least sign of activity has been noticed in July and August and in mid-winter.


178

COYPU AT MINSMERE

A further increase in numbers with a spread to new areas was evident in late autumn and early winter of 1960. A count of the population in the very extensive reed-beds was impossible ; it was estimated that roughly 200 were present on 31.8.60 when it was decided to reduce the number by shooting and trapping. By early autumn, 1962, activity had occurred in all parts of the marsh and this spread might have been due partly to disturbance from control measures and from natural predators beginning to exploit the new food supply. By this time, the population had been reduced approximately to the status of two years previously and areas of 100% habitat destruction were so small as to be negligible. EFFECT UPON

BIRDS

Floating birds very seldom show any concern at the close proximity of coypu. One was often seen swimming through a group of ducks or ducklings and the birds did not move away even when the animal was as close as 18 inches. On one occasion, an adult coypu was eating the reed stems growing through the edge of a nest on which a coot (Fulica aträ) was quietly incubating whilst the bird's mate was swimming, apparently without concern, a few yards away. Some weeks later however, when these birds had small young, the coots were observed trying to force some very small coypus under water. The pups put up no resistance and an adult did not come to their rescue. The declining numbers of water fowl and the disappearance of breeding marsh harriers from other large reed-swamps in East Anglia have been attributed partly to the presence of coypus and their destruction of birds' habitat. At Minsmere with the present rate of control, the ecology of the marsh has been only a little affected but pairs of little grebes (Podiceps ruficollis) have reduced from ca. 12 pairs in 1959 to three pairs (two unsuccessful) in 1962 and the one pair of great crested grebes (P. cristatus) failed to rear any young after two attempts in 1962. No instances of a coypu's aggressive behaviour towards any bird has been witnessed but coypus have often been seen sitting on any sort of small island or platform and it is probable that birds' nests are inadvertently destroyed in this way. CONTROL BY THE WARDENS

A double-ended wire funnel trap 15" x 15" x 4 ' long was found to be very successful and six more were brought into use on 2.5.61. T h e use of bait, e.g., sugar beet, apples, carrot leaves, in the traps was soon found to be unnecessary and a trap placed on any new track soon caught a coypu. It was rare to catch more than one at the same position on a track, though occasionally more than one pup (once four) entered a trap together.


179

COYPU AT MINSMERE

These cage traps are very robust and when sprung the entrance doors are automatically locked down at 45°, so securely that from outside a man can barely force one of the doors up four inches. Yet, such is the desperate strength of a large adult coypu when trapped that about a dozen have escaped by forcing their way under a door as the trapper arrived. The most effective and convenient use of the traps was to concentrate them in one area at a time, moving them to a new site of activity when no more coypus were being caught. In two years up to 30.9.62, 320 coypus were destroyed on the reserve :— caught trapped shot by dog hand Pups up to three months Adults 5 to 25 lbs.

33

36

6

111

133

1

Compared with the 100,000 estimated to have been killed in 1961, mostly in densely colonised areas in Norfolk, this is a small contribution to the national campaign against the coypu. There are, however, now many fewer coypus at Minsmere than when control began and it would appear that the measures being taken here are an effective check on the colonisation of this new area.

CONTROL BY NATURAL

PREDATORS

The coypu is a wild introduced species, native to South America. Its eminently successful spread after a small number escaped from a " nutria " farm in 1937 has been due not only to exploitation of a wealth of suitable habitats in Norfolk and Suffolk but to the absence at first of any significant control by natural predators. By the end of 1960, Ellis (1960) was able to report only a few cases of coypu being attacked by rats (Rattus sp.), fox (Vulpes vulpes), stoat (Mustela erminea), bittern (Botaurus stellaris), marsh harrier and owls (Strigidae). At Minsmere, no positive act of predation has been witnessed though on half a dozen occasions harriers were seen carrying prey which appeared to be small coypu. There is much more circumstantial evidence of attack by ground predators, e.g., the remains of 20 very small coypus were found along 200 yards of path—the skins had been turned inside out and all the flesh and brain eaten. These remains had not been on the path on the previous evening. Rats have often been seen at coypus which had been shot and a stoat was seen on a corpse which was a week old. That other larger predators were taking coypus was evident from the occasional complete disappearance overnight of shot adult coypus, some weighing 20 to 25 lbs.


180 F O O D AND HABITAT

COYPU AT MINSMERE DESTRUCTION

Coypu activity occurs in separated parts of one large area of a roughly even distribution of plant species. Areas of destruction are focal and " buildings " exhibit a clumping tendency, similar to that described from a study area in Poland (Hillbricht and Ryszkowski, 1961). Trapping and shooting, on a somewhat small scale but fairly persistent, in newly infested sections as they are discovered, has so far prevented 100% destruction of plants in any Community of the Minsmere marsh and nowhere in the shallow meres is the normal rate of expansion of the reed beds checked significantly. Most severely attacked are sea clubrush and sedges especially where either of these plants form islands in very shallow water or dried-out meres. Young shoots are grazed in the spring and the tops of the roots eaten in autumn. Colonies of sedge or rush within a reed bed suffer as much from trampling as from being eaten. Reed-mace ( T y p h a latifolia) is readily eaten and some small groups have disappeared. Stems and leaves of yellow iris {Iris pseudacorus) are cut off at ground or water level and left lying. Three large green fruits of this plant were partly chewed away and tooth marks were similar to those seen on an apple eaten by a coypu. Short grass on the paths through the marsh is well grazed by coypus of all ages. Reed is eaten at its edge with water. When it can, an animal sits up on its tarsi like a squirrel (Sciurus sp.) and pulls down and holds a leaf to its mouth with its front paws ; in deeper water the plant is felled. In summer and autumn a coypu has many times been observed to dive in a shallow mere, Surface with the white rhizome of reed showing in its mouth, then settle down, body nearly submerged and chew its way steadily forward with its lower jaw always under water and occasional sideways tugs of the head. The rate of progress was timed at four feet in twelve minutes. This method of feeding, incidentally, gives the impression that it is eating surface water plants that may be around it. In hard weather in winter, rhizomes which had been brought to the surface by a mechanical digger were taken but only in small quantities, the coypu sometimes swimming through thin ice to get at this food frozen on the water. Sign of coypu on the marsh has been hard to discover in periods of hard frost and snow. DĂźring the severe freeze of the first week of January, 1962, only two tracks in the snow were found and the calls of the coypu (a sheep-like " maaa ", but softer) were not heard. Calls and signs were much more apparent with the thaw. Whilst the marsh was under ice, two large coypus were shot in a mixed wood and three more on farm land up to a mile from their normal habitat. Attacks on crops (cereals, beet) on fields bordering the marsh are hardly ever discovered.


COYPU AT MINSMERE

181

BURROWS

The digging of holes is on a very small scale and occurs only in steep banks. Excavations appear to be for two reasons :— ( 1 ) ACCESS TO WATER. Six cases were found where tunnels were dug at ca. 45° from water level through a three foot vertical bank to the surface of the earth, and two of these had similar tunnels in the opposite bank of the ditch. In the case of an exactly opposite obstacle in a coypu's highway, i.e., a steep-sided embankment between two areas of water, holes were dug right through in two places and two were dug only partly through.

(2) ROOSTING. An artifically dug mere of ca. § acre has steep sides of clay. In the spring of 1959, four holes ca. 4 feet long and inclining upwards were dug by coypus at water level ; one of these was expanded from the original hole of a water-vole (.Arvicola amphibius). After a drop of a foot in the water during that dry summer, three of these holes were abandoned and three more dug at the new level. By early October, when the water was very low, another hole was dug at the water's edge and one of the original holes remained in use despite access to it being by a nearly vertical 18" slope on the clay. T h e hand-reared young coypu (see below), when given his freedom, dug a hole in fifteen minutes three feet long with a turn to the right at the end, in the soft sand along-side the assistant warden's hut. It slept in this hole during daylight, the number of hours inside apparently depending upon its appetite. BREEDING

The reproductive rate is about the same in Europe as in the animals' native South America. Breeding occurs throughout the year with up to five litters in two years and two to 11 young per pregnancy (Laurie, 1946). At Minsmere, a litter of 11 was seen once and very small young occurred in all months of the year with minor peaks in April to June and late October to early December. On only two occasions were young observed suckling from a female while she was swimming (the mammae are situated on either side of the spine). The young are precocious and can swim and crop Vegetation within a day of birth (Matthews, 1952). On the Minsmere marsh, small young feeding were mostly seen on short grass. There were occasional instances of naivete ; a few, up to ca. three months old, were easily caught by hand in shallow water or in Vegetation. Once a group of small young appeared near a man using a motorised under-water reed cutter which roars like an unsilenced two-stroke motor cycle. T h e rapidly moving teeth of the the machine were brought to within


182

COYPU AT MINSMERE

an inch of the nose of one of the young which even then did not move away. The voice of a coypu can sometimes effectively be imitated, and one will often answer at night. In mid-afternoon, a young coypu was brought 150 yards along the path to the feet of five people by the Warden calling " maaa " at intervals. A

HAND-REARED YOUNG

COYPU

A recently-born male weighing 184 gm. was taken on 11.12.60. Whereas the quantity of milk suckled in the wild may be comparatively small at each feed (Ellis 1960) this pup was avid for cow's milk warm or cold and for the first four weeks would take 20 to 40 cc. nine times per 24 hours, from a doll's feeding bottle. Dßring its second month it could take 42 cc. at a time before turning away from the bottle. The milk was additional to a varied diet of vegetable matter and was discontinued at two months when it ceased to cry at night, much to the relief of assistant Warden P. J. Makepeace. Up to three months, it still tried to suck the teat of the empty bottle. On 30.3.61 (ca. 111 days old) it weighed 1588 gm., representing a monthly increment of 383 gm., comparing with the average monthly gain of 400 gm. quoted by Laurie (1946) in a coypu's first year. The only animal matter it ate was what may have been contained in chocolate and various pastries—jam tarts as well as pieces of bread and butter were especially liked. It ate a wide variety of garden vegetables but only the leaves of carrots. Only a little of banana was eaten at a time. Strawberries and grapes were taken keenly and were held in the forepaws, either while lying prone on its stomach, its side or its back, or sitting upright on its tarsi like a squirrel. It would continue to eat from food in its paws, while held upside down by its tail. For three months, until its faeces in the house and its predilection for rose leaves in the garden could no longer be tolerated, it had a free run. At this age, it easily climbed out of a large pen with two foot vertical wooden walls. When two feet of oneinch wire netting were added, it immediately learned to surmount this, making much use of its incisors when climbing and readily dropped four feet to the ground outside. From the start and until four months old, when it began to exhibit copulatory ability, it was quite docile. Thereafter, it would occasionally bite the hands and ankles of strangers but not its human foster parents. At five months, when it had already apparently passed puberty, it was taken for a long walk on the marsh paths, without a lead. It passed many tracks of coypus and showed little or no interest in them nor in the fresh droppings, but kept quite close to my heels and did not attempt to go off into the reeds.


183

COYPU AT MINSMERE

Reingestion of its droppings, when it was six months old, was witnessed by Lord Cranbrook and the writer. It picked up in its forepaws two faeces which were stuck together along half of the flat side, out of eight of the same colour which it dropped in three minutes whilst lying on its back and being petted. This was in daytime and the reingested pair of droppings had not been taken direct from the vent as a rabbit does with night droppings (Thompson and Worden, 1956) nor were they mucuscovered. At six months, it broke half of the top left incisor when dropped onto concrete, a jagged piece of the hard orange enamel projecting beyond the cleanly broken dentine. This incisor grew at the rate of four mm. in ten days and was fully restored, with a worn-sharp cutting edge, in six weeks. The enamel on the new part of the tooth, near the gum, was much less pigmented. No external parasites were found on this nor on any other coypu at Minsmere, though the tarne one several times a day sat up and scratched its flanks and belly in the same sequence and rhythm observed in wild coypus. When it was removed to another free run around the watchers' huts at the edge of the marsh, at about six months, it spent much time in the reed beds but came back three or four times daily to be fed by hand. It readily came up to the feet of any visitors it saw on the marsh paths and inevitably, in early September, 1961, it was found dead with a fracture of the skull.

REFERENCES

Ellis, A. E. 1960. T h e Coypu threat in East Anglia. 29.12.60 : 1590-1591.

Country

Life,

Hillbricht, A. and Ryszkowski, L . 1961. Utilisation of habitat by coypu. Ekologia Polska—Seria A. IX. Nr. 25. Laurie, E. M . O. 1946. T h e Coypu (Myocastor coypus) in Great Britain. J. Anim. Ecology 15.1 : 23-34. Matthews, L . H . 1952. British Naturalist Series (London).

Mammals,

Thompson, H . V. and Worden, A. N . 1956. New Naturalist Series (London).

209-211.

Collins'

T h e Rabbit, 26-31.

Trist, P. J. O. 1952. Ecology at Minsmere. V I I I pt. I I : 66-72.

Trans.

New

Collins'

S u f f . Nat.

Soc.,

Coypu (Myocastor coypus) at Minsmere Bird Reserve  
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