Conservation of the dusky seaside sparrow on Merritt Island, Florida

  • Published on
    18-Oct-2016

  • View
    217

  • Download
    0

Transcript

  • Conservation Around the Worm 175

    ce programme et son caract~re international s'affirmera encore, puisque l'activit6 d'EUREL est d6j~t sollicit6e en Espagne et en Ecosse. La sauvegarde des oiseaux de proie n'est pas le seul objectif: des r6serves libres sont aussi h l'&ude pour assurer aux oies sauvages et aux grues leurs lieux de rassemblement et d'hivernage en Europe. Formule souple et pratique, fond6e sur la science &ologique, la r6serve libre contribue h con- server les richesses en faune et en flore de notre con- tinent, sans distinction de fronti6res.

    PAUL GI~ROUDET, Collaborateur scientifique du WWF, 1110 Morges, Suisse

    CONSERVATION OF THE DUSKY SEASIDE

    SPARROW ON MERRITT ISLAND, FLORIDA

    During the spring of 1968 1 conducted a singing male census of the endangered Dusky Seaside Sparrow (Ammospiza nigrescens), which was traditionally thought to be confined to the salt marshes on Merritt Island, near Cape Kennedy, Florida. Formerly the species was abundant over an area of approximately 6,000 acres (2,430 ha) of the Island, and by my cal- culation must have numbered about 2,000 pairs. An incomplete census from 1961-63 revealed a much- reduced population of 70 pairs (Charles H. Trost, in litt.), and now this bird is on the official United States list of rare and endangered species. Repeated visits to the remaining aggregations, of which there were three in 1968, and the mapping of the location of singing males, turned up only 33-34 males, 4 or 5 of which were wandering non-territorial birds or known to be unmated. For reasons of habitat selection or food supply, the species is restricted to the lower parts of the marshes, where the zones of the short grass Distichlis spicata and of the tall grass Spartina bakeri overlap.

    The primary cause of the species' decline is deterio- ration of habitat. Since 1957 the marshes have been impounded for the control of mosquitoes, in particular Aedes sollicitans and A. taeniorhynchus. These species lay their eggs on mud, and the larvae develop in tem- porary pools left by tide or rainfall. Egg-laying is pre- vented by the flooding of the impoundments with up to 12 inches (30.48 cm) of water during the mosquito breeding season (April to October). This practice, however, has a detrimental effect on the vegetation; prolonged flooding, especially of the lower marshland to which the bird is restricted, asphyxiates the standing vegetation and prevents further reproduction, trans- forming the marsh into a habitat more suitable for

    waterfowl and wading birds. Thus, mosquito control and the waterfowl management objectives of the Merritt Island National Wildlife Refuge, of which the salt marshes are a part, are not incompatible. But the best interests of the Dusky have up to now been ignored. Therefore, for any conservation programme to succeed, the marsh must be thought of in its social context, with consideration given to mosquito control, duck-hunting, other species of non-hunted birds, and the rarity of the Dusky. The question of Dusky management resolves itself into how compatible it is with other interests, and, if it is incompatible, to what degree.

    Saving the Dusky is tantamount to preserving and re-establishing the vegetation, at least in those three impoundments where there are the three remnant colonies (1,357 of the 7,565 impounded acres). Of these 1,357 acres (540 ha) only 200 are currently suit- able as a habitat, the vegetation of the rest having largely died. Salt-marsh plants are adapted to with- stand considerable flooding, and there is evidence that, towards the southern parts of their ranges in the northern hemisphere, these plants can tolerate increased periods of submergence--presumably be- cause intensified insolation allows photosynthesis to occur while the plant is submerged. It is usual for salt marshes on the east coast of Florida to be flooded continuously from July to September (M. W. Provost, personal communication), and Sincock's (1958) data corroborate that 95 per cent of the parts of Spartina bakeri are found at elevantions which are flooded from 0 to 21 per cent of the year (or up to 2 months). The Distichlis, occupying a zone lower in the salt marsh (Chapman, 1960, pp. 256-9), can presumably withstand longer submergence than this. Both species can withstand a considerable range of salinities. The Distichlis is able to reproduce vegetatively by rhizomes, but the Spartina cannot do this and must rely on some seed production and hence conditions suitable for germina- tion (probably a moist but unflooded, and not too saline, soil surface).

    In the light of these considerations, it would be advisable either to break the dikes, allowing the natural processes of invasion of the marsh by high tides and drainage of rainwater, or to pump the impoundments dry for all but 2 months of the year. Any freshening of the impounded marsh in late summer by accumulated rainfall and the consequent volunteering of the Cattail (Typha domingensis) could be rectified by pumping saline water into the impound- ment. Until reflooding occurs, mosquito control can be accomplished by the use of the larvicide Paris green, which has been approved by the United States Fish and Wildlife Service for use on federal refuges. There is also

  • 176

    evidence that the drawing down on marsh impound- ments is beneficial and indeed necessary to continued marsh productivity (Kadlec, 1962), and continued waterfowl use could result as a consequence of sus- tained food and cover and interspersion of cover and water.

    This, of course, is the barest outline of a conserva- tion plan and is intended only to point out in principle some of the things that must be considered. Unfore- seeable effects, and even foreseeable difficulties, such as the provision of the necessary salinities, periods of submergence, conditions for the setting of seed and for germination, and invasion by unwanted plant species, will arise and have to be dealt with pragmatically. Different treatments should be applied to each of the three impoundments that are known to contain aggre- gations in order to avoid possible loss of the entire population during the trial-and-error process. Fortu- nately, it appears in this case that with some effort, intelligent management, and a certain amount of good fortune, the vegetation could re-establish itself, and the Dusky population recover some of its former numbers and reinvade newly-created habitats--even while other management objectives were being attained.

    I found another, healthier population of this en- dangered species surviving in the St John's River marshes on the Florida mainland. As its habitat and the threats to its continued existence are somewhat different, its ecology and management are being dis- cussed in a separate paper.

    References

    CHAPMAN, V. J. (1960). Salt Marshes and Salt Deserts of the World. (Plant Science Monographs, edited by N. Polunin.) Leonard Hill, London, & Interscience, New York, 392 pp., illustrated.

    KADLEC, J. A. (1962). Effects of a drawdown on a water- fowl impoundment. Ecology, 43(2), 267-81.

    SINCOCK, J. L. (1958). Waterfowl ecology in the St John's River valley as related to the proposed conservation areas and changes in the hydrology from Lake Harney to Fort Pierce, Florida. Florida Game and Fresh Water Fish Commission, Federal Aid Project, W-19-R, 122 pp.

    BRIAN SHARP, Department of Wildlife Ecology, University of Wisconsin, Madison, Wisconsin, USA

    CONSERVATION OF THE GIANT

    PIED-BILLED GREBE OF GUATEMALA

    The Giant Pied-billed Grebe (Podilymbus gigas) is evidently endemic to Lake Atitlan, Guatemala-- hence its alternative name of Atitlan Grebe-- and is

    Biological Conservation

    one of the rarest birds of all Central and North America. As a flightless waterbird of such extremely limited range, it could all-too-easily be exterminated at any time. Fortunately, however, a programme was instituted some yeals ago by Anne LaBastille Bowes, of Cornell University, to study and preserve it. This programme, supported particularly by the National Geographic Society and the World Wildlife Fund, has been actively pursued, especially by Anne Bowes, and now the Grebe population has increased, a total of 116 adult birds being counted early in 1968. This represents an increase of 10 per cent from the June 1967 census and of 20-25 per cent from the population 'low' of 1965-66.

    Limitation of numbers have been chiefly by shooting and poaching by local residents, cutting of shoreline aquatic vegetation for home industry, etc., and pre- dation and competition for food by introduced Largemouth Bass. There was also a lack of conserva- tion education and conscience within the country. Latterly, however, the situation has improved, as a Presidential Decree prohibits the cutting of reeds and cattails during the critical period of reproduction of the Grebes (1 May to 15 August). Furthermore, as an indication of governmental concern, to awake public interest a set of postage stamps 'commemorating' the Giant Grebes and Lake Atitlan is being issued by Guatemala.

    More important to conservationists is the fact that, as the result of her promotion work, Anne Bowes has succeeded in interesting the governmental authorities to ensure continuation of the programme by becoming responsible for a special National Refuge on Lake Atitlan for the conservation of the Giant Grebe. This Refuge was inaugurated under the general sponsorship of the Government of Guatemala, in Panajachel on 15 June 1968; numerous dignitaries were invited, and 65 persons attended the actual dedication.

    On this occasion, speeches were made by the Minister of Agriculture, the Vice-Minister of Agricul- ture, the Chief of the Division of Fauna of the Ministry of Agriculture, the Director of the Guate- malan Section of the International Council for Bird Preservation, and finally by the Director of the 'Operacion Proteccion del Poc' (Operation 'Protection of the Giant Grebe'), Anne Bowes, who transferred control of the Operation to the Guatemalan Govern- ment. It is assumed that officials of their Ministry of Agriculture will be responsible for the future main- tenance of the Refuge and conservation campaign, and so the former Director has sent a list of recommen- dations to the Vice-Minister of Agriculture and other officials, and has offered further assistance on a consul- tant basis at any time.

    EDITOR

Recommended

View more >