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Diseases of Seaducks in Captivity

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Diseases of Seaducks in Captivity Diseases of seaducks in captivity NIGELLA HILLGARTH and JANET KEAR For many years the Wildfowl Trust has Bufflehead Bucephaia albeola are, on the monitored the health of its collections by other hand, notoriously difficult to breed carrying out post-mortem examinations. (Williams 1971), and the Hooded Merganser Detailed records have been kept by J. V. M. cucullatus is only a little easier (Lubbock Beer (1959—1969), by N. A. Wood 1973). (1970-1973), and by M. J. Brown sub­ The difficulty with which these ducks are sequently. This analysis of the accumulated bred is, to some extent, reflected in the records is the first of a series that will numbers available from the Wildfowl Trust’s describe the cause of death in the various collections at post-mortem. For instance, wildfowl groups. eiders predominate in the records, and saw­ There are seven genera, and 18 species, of bills are commoner than scoters. However, seaducks (M ergini) including the eiders eggs have been collected on a number of oc­ (Johnsgard 1960). All except one species in­ casions from the wild, and hatched artificial­ habit the higher latitudes of the northern ly, so post-mortem findings from dead dow­ hemisphere; the rare exception, the Brazilian ny and juvenile birds do exist, even for M erganser Mergus octosetaceus, has never species that have seldom bred in captivity. been maintained for long in captivity. The whole group is generally difficult to keep and to persuade to breed. There are many M aterials reasons for this; seaducks are divers and animal eaters; most of them spend the Post-mortem data from 641 seaducks dying winter, and some breed, on salt water; those between 1959 and 1976 have been examined. which breed north of the arctic circle These concerned a total of 295 adults, 134 experience low levels of pathogenic juveniles and 222 downies and, for con­ organisms; and all species take at least two venience, have been divided into four groups years to reach sexual maturity. of species (Table 1). An adult is defined as a bird that survived to its first January. A juvenile was fully feathered, but died in its History in captivity first autumn or in early winter (before 1 January). A downy was any young bird not Of the eiders, only the European Eider fully feathered. Somateria m. mollissima is commonly kept and bred (London Zoo appears to have bred it for the first time in 1841). The King Eider Results S. spectabilis bred first, at Slimbridge, in 1961, and the Spectacled Eider S. fischeri in Seaducks generally survive for only a short 1975. Steller’s Eider Polysticta stellen has time in captivity. The average age at death of never laid in captivity. Scoters are even more adults was three years and eight months (this difficult to breed. The Common Scoter figure is based on the 49-5% of those Melanitta nigra nested successfully in cap­ examined whose age was known. Females tivity in 1971 but the other species have died earlier than males at an average of only never done so. The Harlequin Histrionicus three years, while males died at four years histrionicus bred as recently as 1977. The six months. One-year-old birds constituted European Goldeneye Bucephaia clangula 24-7% of the total (in other words, a quarter has been established as a breeding bird since never reached breeding age), and the oldest 1909, and Barrow’s Goldeneye B. islandica record was of a male European Goldeneye since 1937, but neither nests particularly free­ that died at 16 years. ly in waterfowl collections. Of the sawbills, There was a significant difference (Figure the Red-breasted Merganser M e r g u s 1) between the number of males and females s e n a to r nests in the wild in Britain as far dying during March 2 = 8-2, P > 0-01), south as 53°N, and the Goosander M. and a smaller but significant difference m erganser only a little farther north, so it is between the number of males and females not surprising that they have been reared dying during October (x1 = 4-3, P > 0-05). more frequently in captivity than other Males seem to be under stress in early spring M ergus species. The Smew M. albellus and (perhaps due to competition for mates) and Wildfowl 30 (1979): 135^» 135 136 Nigella Hillgarth and Janet Kear again in autumn, whilst in eclipse, and more ease found in dead adults, with 34% of adult easily contract disease at these times. seaducks, 8% of juveniles, and one downy, Females seem to be under stress during the found to have advanced tuberculosis at breeding season, mortality reaching one peak death; 49% of adult sawbills or M ergus in July and another in November. species had died of this cause. At post-mortem examination a primary All captive wildfowl may contract tuber­ cause of death was assigned, and it is those culosis, but seaduck seem to have very little conditions that are discussed below. resistance. Nevertheless, it predominately affected older birds: of the 55 adults whose Tuberculosis age was known, death occurred on average Avian tuberculosis was the commonest dis­ at 4^ years, 25 females averaging 4 years, Table 1. The number of seaducks dying in Wildfowl Trust collections, 1959-1976 Ad <? Ad ? Total Juv c? Juv ? Total Downy c? Downy ? Total Eiders 64 60 124 22 38 60 25 24 49 Somateria & Polvsticta Scoters 9 13 22 3 3 6 4 4 8 Melanitta Goldeneyes 45 24 69 16 17 33 37 37 74 Histrionicus Clangula & Bucephaia Sawbills 42 38 80 16 19 35 41 50 91 Mergus Totals 160 135 295 57 77 134 107 115 222 32 SEADUCK DEATHS PER MONTH 30_ 28l 261 2U 22 O'20 o 18_ _ §16. o toS u . ou_ 12lz- CO8510! 3 ö" z 6 . L. 2I 0 MONTH OF DEATH Figure 1. Numbers of male and female seaducks dying per month in Wildfowl Trust collections, 1959-1976. Diseases of captive seaducks 137 and 30 males averaging 5 years. This is regular testing, thus giving the opportunity almost one year later than the overall age at for eliminating diseased specimens from a death. collection before they can contaminate their The bacteria Mycobacterium avium usual­ pens heavily, is obvious. ly invade the liver and spleen, sometimes the gut and lungs, forming multiple lesions. They Aspergillosis are spread in the droppings of infected birds, Of the birds examined, 17% of adults, 31% and in contaminated food and water. Wild of juveniles and 27% of downies were found birds also spread the infection, especially to have died of advanced aspergillosis. gulls (Laridae), doves (Columbidae). Phea­ Eiders seems especially susceptible, with san t Phasianus colchicus and Starlings S tu r­ 30% of the adults, 47% of the juveniles and nus vulgaris, and wild eiders seem to die of 47% of the downies affected. Figure 2 shows the disease fairly frequently (Garden 1961; the incidence of aspergillosis in adult eiders MacDonald 1965). month by month; two peaks are apparent, Mycobacterium avium is very resistant to one in spring and another in autumn. disinfection and can remain viable for three Aspergillosis is caused by the fungus years in the soil; it is therefore very difficult Aspergillus fumigatus. A widespread disease to eradicate the contamination from a water­ of all birds and many mammals, it is com­ fowl collection. The only recommended monly encountered in wild and captive procedure is exposure to the ultra-violet in waterfowl. The fungus grows readily on sunshine rays, and keeping pens unshaded. damp foodstuffs and rotting vegetation such This is obviously not completely compatible as hay and straw, and large numbers of with good husbandry, since breeding may microscopic airborne spores are produced, depend upon a cover of vegetation in the particularly in the damp days of October. summer when disinfection from the sun’s These spores may become pathogenic when rays has its greatest potential. As yet, no they are inhaled into the respiratory tract, effective vaccine against avian tuberculosis and give rise to large spore-producing has been produced. Work is being done on plaques in the lungs and air sacs; it is the the possibility of testing for the presence of toxin produced by these fungal growths that progressive avian tuberculosis in live water­ often kills the affected bird. fowl. Preliminary results are encouraging Waterbirds in captivity seem much more (M. J. Brown pers. com.). The advantage of susceptible to aspergillosis than do land Figure 2. Numbers of male and female eiders dying per month of Aspergillosis in Wildfowl Trust collec­ tions, 1959-1976. 138 Nigella Hillgarth and Janet Kear birds; penguins (Spheniscidae), pelicans conception that seaducks take a high protein (Pelecanidae), flamingos (Phoenicopteridae), diet in the wild. Eiders eat whole mussels, divers (Gaviidae), petrels (Hydrobatidae) and mergansers take whole fish including the and some shore birds (Charadriiformes) are relatively indigestible shells, bones, scales, especially susceptible. Dathe (1962) pointed gut and gut contents. Ungutted sprats, for in­ out that all seabirds have salt extracting stance, contain only about 15% protein nasal glands that atrophy when the birds are (Murray & Burt 1969). Seaducks often find kept on fresh water, and he suggested that commercial pellets intended for trout and this renders them more prone to airborne in­ dogs particularly palatable, but these foods fections. Kaben & Schwarg (1970) also should not be fed as a sole diet (Kear 1976). suggested that the salty nasal secretion of marine birds protects them to a large degree Im pactions from invasion by Aspergillus. Some 3% of all adult seaducks, 17% of Treatment has up to now been unsatisfac­ juveniles and 4% of downies had impactions tory, partly because diagnosis is difficult.
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