(Perdij( Perdix) in the Canadian Prairie
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WESTERSKOV: ECOLOGY OF PARTRIDGE IN CANADA 23 a prominent land-mark just west of the present Meteoro- COCKAYNE, L., 1928. The vegetation of New Zealand. logical Station. Norfolk Island pines are common in 2nd edition. Engelmann, Leipzig. many coastal districts of New Zealand, of course, but mature cones are rarely produced. On Raoul, several MORTON, E. K., 1964. Crusoes of Sunday Island. New trees had formed numerous cones which seemed to be Zealand edition. Reed, Wellington. fully grown. Raoul Island and Norfolk Island are on the same latitude, but this probably does not explain OLIVER, W. R. B., 1910. Vegetation of the Kermadec why the species usuaJly fails to form viable seed in Islands. Trans. New Zealand Insi. 42: 118-175. New Zealand. WRIGHT, A. C. S., and METSON, A. J., 1959. Soils of Raoul (Sunday) Island. N.Z. D.S.l.R., Soil Bureau REFEREN CES Bulletin 10. CHEESEMAN, T. F., 1888. On the flora of the Kermadec YUNCKER, T. G., 1943. The flora of Niue Island. Islands. Trans. Proc. New Zealand Inst. 20: 151-181. Bernice P. Bishop Museum Bull. 178: 30. WINTER ECOLOGY OF THE PARTRIDGE (PERDIJ( PERDIX) IN THE CANADIAN PRAIRIE KAJ WESTERSKOV' Department of Zoology, Un iversity of Otago, Dunedin Of the higher vertebrates living in northern The boreal forest gives way southwards to regions of the Northern Hemisphere, birds have the prairie through an ecotone, the Aspen Park- a pronounced advantage over mammals in their lands, dominated by aspen poplar (Populus facility for escaping winter through flight to tremuZoides). Settlement northward from the warm southern climates. Very few birds stay prairies has appreciably opened up the aspen behind when southern migration transfers the parklands (Fig. 1), and it is in this zone and vast bird populations to suitable wintering in farmland districts cleared in the boreal forest grounds. immediately to the north of it that the partridge In North America more birds are found in is found at the northernmost extension of its winter in the boreal forest (the northern North American range. coniferous forest or taiga) than in the prairies From liberations near Calgary, south-western to the south. The forest provides more food Alberta, in 1908, partridges spread rapidly and shelter and various groups are present north-east and south and now occupy practic- such as grouse (Tetraonidae), woodpeckers ally all of the Canadian prairie as well as the (Picidae), titmice (Paridae) and others. aspen parklands. Along roads, clearings and settlements penetrating into the boreal forest, small partridge populations are also present. THE PRAIRIE WINTER The Canadian prairie, forming the vast habitat of the partridge, measures some 900 . This study was carried out during July 1961-July 1962 while the author was attached to the Depart- ment of Zoology, University of Alberta, Edmonton. The project was financed through a Post-doctorate Fellowship from the National Research Council of Canada, for which I am very grateful. For leave granted I am also indebted to the New Zealand Depart- ment of Internal Affairs, Wildlife Division. The assistance of Dr. D. M. Ross, Head, Department of FIGURE 1. Prairie farmland in the Aspen Park- Zoology, University of Alberta and his staff is grate- land zone in northern Alberta and Saskatche- fully acknowledged. I also wish to thank Mr. H. N. Southern, Bureau of Animal Population, University of wan, iust south of the boreal forest and the Oxford, who was Visiting Professor at the University northernmost extensions of the partridge range of Otago in 1964, for r~ading the manuscript and in North America. Early April 1962. helpful suggestions. WESTERSKOV: ECOLOGY OF PARTRIDGE IN CANADA by 400 miles at its northernmost extension. It WINTER BIRDS IN THE PRAIRIES is almost triangular~ to the west bordering the foothills of the Rocky Mountains, to the north In the open farm landscape of the prairies a falling line from north of Edmonton in the species and numbers of wintering birds are Alberta to Winnipeg, Manitoba; the border to low. Only two passerines, the snow bunting the United States forms the southern geo- (Plectrophenax nivalis) and the redpoll graphical limit~ but partridges are common in (Carduelis f/ammea) are regularly seen, feed- the adjoining states of Montana, North Dakota ing 011 seeds of forbs and grasses protruding and Minnesota. above the snow; both species are winter visitors from further north and occur in wandering The winter in the Canadian prairie is charac~ flocks. Magpies (Pica pica) are resident and terised by temperatures continuously below common throughout the area; partridges killed freezing for 4-6 months and as low as 50°F. and wounded by cars on the road are eaten by below zero, with little snow and little wind. magpies. Two owls are present, the resident In this area partridges survive winters of an great horned owl (Bubo virginianus) of the intensity not experienced in their native Euro- parkland poplar stands, and the snowy owl peon range. (Nyctea scandiaca), occuring irregularly as a winter visitor from the north. Usually near hedges, scrub or poplar stands a few pheasants (Phasianus colchicus) and sharp-tailed grouse (Pedioecetes phasianellus) are seen. Pheasants are more common further south and are here at their very northern limit and do not pene- trate into openings in the boreal forest as does the partridge; while sharp-tailed'grouse become more plentiful to the north. A few ruffed grouse (Bonasa umbellus) are also seen along hedges and near forested areas. Partridges do not compete for food with snow buntings and redpolls~ as comparison of food habits showed; partridges are primarily eaters of waste grain during winter (d. \Vesterskov in press). Habitat requirements of partridges overlap somewhat with those of pheasants and sharp-tailed grouse, as do food requirements, but they may not compete directly or indirectly; partridges prefer the open field habitat while the other two FIGURE 2. Diagrammatic representation of species resort to scrub and thickets although winter conditions in the Edmonton area in frequently feeding in the open. Both species of relation to partridge ecology. Columns indicate owls occasionally kill partridges. monthly snow-depths. WINTER ADAPTABILITY OF THE PARTRIDGE While the partridge belongs to a southern Fig. 2 relates daily mean temperatures and faunal element in Eurasia, the advance of monthly snow cover to partridge ecology in agriculture towards the north has caused an winter, based on conditions in the Edmonton enormous expansion of its range far into the area. From late October to mid-March the boreal forest biome (Westerskov in press); both temperature is constantly below freezing; a mean minimum temperature of just above zero in Scandinavia and in Russia. This northward OF. is reached in January. December-January extension demonstrates an ecologic amplitude are also the two months with deepest snow, up and plasticity not expected considering the to 10 in. Due to easy wind-movement of the large, long established populations in north- fluffy dry snow and evaporation caused by western Europe with generally mild winters. almost continuous sunshine, the snow cover is Winter temperatures at Edmonton, Alberta not uniform; there is for instance less snow (from November-March) are much lower than on south-facing slopes and open fields. within the partridge's native European optimum VVESTERSKOV: ECOLOGY OF PARTRIDGE IN CANADA 25 for the species (McCabe & Hawkins 1946,S). Foot and leg adaptations Limiting factors in the east appear to be deep When walking on hard wind-blown snow winter snow as well as high summer tempera- (Fig. 3), partridges do not sink through as do tures, in particular high ground temperatures heavier bodied animals. In loose snow, par- to the south (Westerskov 1964), and excessive tridges must furrow their way through, but the summer rain (Dale 1942). light snow-fall characteristic of the prairies is What, then, is the explanation of the out- a major factor enabling free movement and standing success of the introduction of the par- easy access to food. tridge in the Canadian prairie? How does this While the partridge is not so well adapted comparatively small bird survive extreme cold to walking on snow as are arctic and sub-arctic in the long winter, in constant snow for months species such as snowshoe hare (Lepus ameri- on end? canus) and ptarmigan, the comparatively long MORPHOLOGICAL ADAPTATIONS tarsi (longer than in all three species of ptarmigan and spruce grouse, Canachites The partridge, weighing in winter about canadensis) enable it to move unhindered in 400g., is intermediate in size between the small snow-depths of 2k in. or slightly more without species of quail (as Colinus in North America the abdomen touching the snow. and Coturnix in Eurasia), nlainly found to the south of its range, and the larger grouse species The tetraonids have feet well adapted to (as Pedioecetes and Bonasa in North America snow conditions: ptarmigan have feathered toes and Lyrurus and Tetrastes in Eurasia), mainly and the wood grouse have horny papillae found to the north of its range and associated (comb-like fringes) on the toes in winter. In with the boreal forest. The larger the animal, both cases the supporting surface of the foot is the smaller its surface area and heat loss in increased, see Table 1. Ptarmigan have a relation to volume. Arctic and sub-arctic weight loading of 20 gJcm2 and while the par- species and subspecies are therefore larger than tridge cannot measure up to some of the snow- their relatives in warmer climates. The adapted tetraonids such as ruffed grouse and medium-sized partridge can survive extreme sharp-tailed grouse, it is much more capable cold provided it is properly fed. Its body size of moving on snow and has a better weight may be the safe minimum for efficient heat load, foot surface ratio (4S gJcm2) than either control and at the same time the maximum the pheasant or the sage grouse.