Marian KUC 6 Lewer St., Ottawa (Gloucester) Ontario, CANADA K1V-1G9

Wyprawy Geograficzne na Spitsbergen UMCS, Lublin, 1995

STERCORARIUS PARASITICUS (PARASITIC JAEGER) IN FLORA-AVIFAUNA RELATIONSHIPS IN THE HORNSUND AREA (SW SPITSBERGEN)

Relationships between high arctic flora and avifauna are discussed and documented mainly by zoologists. There have seldom been treatments inter-preting this phenomenon from a botanical standpoint.

Several reasons determined the selection of Stercorariusparasiticus as a study subject, most particularly its position in the food chain catena; Jaeger belongs to a group of sea birds which have only slight connections with terrestrial plant cover.

This paper discusses the nesting site (Fig. 1) of Stercorarius parasticus as surveyed by the vegetation transect method, with the aim of defining the influence of this bird on various surrounding plant species.

The strongest direct effect of Stercorarius on vegetation is the destruction of plant growth as its nesting sites, even though only small amounts of plant material were found to be used for nest construction, and only traces of plant remnants have been found in its food. The birds sometimes penetrate grass-land, dwarf shrub communities or well-developed tundra at lower elevations, often picking off flowers, inflorescences of grasses or larger leaves. However, in the Hornsund area no remains of terrestrial plants were found in its excrements, instead there was a considerable amount of algal mass along with small sea animals. This was originally the food of sea birds (mainly ducks and gulls), which Jaeger obtains by robbing its victims in vigorous and noisy air attacks, forcing them to disgorge their crops. The pirate then snaps up the falling contents before the plunder hits water or ground.

The presence of land plants in Jaeger's food was proven by De Korte -1972a & b. At Edgeoya plant content reaches up to 8% (Papaver dahlianum, Poa sp.) and 54% near Murmansk. In my opinion, the absence of land plants in the excrements examined in Hornsund is connected with phenology, both of birds and vegetation. On the other hand, the question of terrestrial vegetation in its food is still open, because this bird is known to eat the stomachs of small vegetarian birds (cf. Kuc 1961, 1964), e.g. Plectrophanex nivalis or chicks of Lagopus mutus.

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The surveyed hillock with Stercorarius nests was 12 m long, 7 m wide, a few meters high above its base, about 900-950m from the sea, 50m a.s.l. and adjacent to the foothill of Ariekammen (512 m a.s.l.) on the flat foreland called Fuglebergsletta. In late summer, when all the birds had gone, the site was scaled by 1 m 2 mesh and selected items connected with bird activities were plotted on each square. This was completed in a time of 4 1/2 hours. From the resulting transect, a botanist can read the following features attesting to the influence of Stercorarius upon adjacent growth (see # 1-20 in Fig. 1).

Dense, high tufts of Syntrichia ruralis (a frequent moss component of dry tundras) formed rings immediately next to the nests ( # 1). Common vascular nitrophiles ( # 2 & 4), all low and rendered depauperate by the birds, grew in limited numbers around the nests or directly on excrements. A single, tall and fertile specimen of the grass Poa alpina (# 3), luxuriant, grew on the bare substrate just at the border of an occupied nest, apparently not at all touched by the birds. Many fragments of Saxifraga caespitosa ( # 5 ) were uprooted and strewn over the nesting area. The single fertile specimens of Saxifraga nivalis ( # 6 ) were also not affected by the jaegers. The same applies to patches of abundantly seeding Draba alpina ( # 7). On the bottoms of nest depressions and around the nests, directly on guano or on organic soil, were many specimens of the nitrophilous alga Prasiola crispa (# 8). Saxifraga oppositifolia ( # 9 & 10) was very common in the area. The moss Drepanocladus exannulatus, a dominant species and mass builder of mesic communities, surrounded the nests and, in some areas, showed considerable degradation as a result of bird activities ( # 11, only its compact stands were mapped). Horsetail (Equisetum cf. variegatum, # 12) occupied southern exposures of the hillock, and evidently has only recently invaded the area of nests. Patches of the common mesic moss Dicranum groenlandicum ( # 13 & 14) showed signs of mechanical destruction, especially along its edges. Lichen species of the genus Cetraria (cf. C. nivalis & C. islandica) occurred over the hillock, but only single specimens grew around the nests ( # 15). A distinct and wide ring of grasses (# 16, several species, all sterile) surrounded the area of the nests. It included a small dense spot of the fertile grass Festuca sp. ( # 17) that was not affected by bird activities. Dry tundra, where clearly affected by SW winds, was dominated by the moss Rhacomitrium lanuginosum and was more heavily fertilized by the Jaeger's guano than elsewhere. A healthy dwarf shrub community with willows (Salix polaris, # 19) advancing on the hillock from the southwest, was in many places badly degraded by the birds ( # 20).

Nests were erected on top of the hill ( # 21), and also at the boundary between well-developed growth and nearly barren ground ( # 24 &25). The nests contained small fragments of willow twigs and straw deposited there by the birds, while other parts of vascular plants, as well as mosses, lichens and duff accumulated there as windblown debris from adjacent vicinities. Only two nests

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(1957, 1958) were mapped ( # 22 &23), but as many as 10 old nest sites, marked by depressions, were encountered. This indicates that the hillock had been used as a nesting place for many years, perhaps by generations of Stercorarius. Around the nests, in a radius of several meters, were many patches of bare ground resulting from the activities of the birds. These probably were the results of accumulative negative effects on the plant growth over a period of many years.

These records show convincingly that Stercorarius adversely affects plant growth around its nests. The cause is mainly by mechanical damage, which is probably inflicted during landing and take off. Even the fertilizing effect of guano was less extensive there than in the other locations which Jaeger frequented, e.g. on its watch-towers. Evidence that jaegers consumed plants around their nests was not found.

The recognition of the relationships between plant cover and its use by birds, especially those linking sea and land avifauna, is an important step in the comprehension of a general tundra ecosystem. Much more could be said about the responses of plant communities to the manuring of tundra by birds, as well as their phenology, which is one of the major geobotanical characteristics of this region. However, such topics are beyond the scope of this article.

REFERENCES

De Korte J., 1972a: Birds, observed and collected by "De Nederlandse Spitsbergen Expeditie" in West and East Spitsbergen, 1967 and 1968-69, second part. Beaufortia 19(257): 197-237.

De Korte J., 1972b: Birds, observed and collected by "De Nederlandse Spitsbergen Expeditie" in West and East Spitsbergen, 1967 and 1968-1969, third and last part. Beaufortia 20(261): 23-58.

Kuc M., 1961: Plant food of the Northern Ptarmigan (Lagopus mutus hyperboreus Sundevall) at Spitsbergen. Ekologia Polska 7/3, ser. В: 237-240 (in Polish).

Kuc M., 1964: A botanical analysis of excrements of the Northern Ptarmigan (Lagopus mutus hyperboreus Sundevall) from Hornsund (SW Spitsbergen). Ekologia Polska 12/24, ser. A: 395-399.

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Fig. 1. Nesting site of Stercorarius parasiticus as shown by the vegetation transect. A. # 1 -25, plotted items. 1 - Syntrichia ruralis, 2 - Cochlearia groenlandica, 3 - Poa alpina, 4 — Phippsia algida, 5 - Saxifraga caespitosa, 6 - 5 . nivalis, 1 - Draba alpina, 8 - Prasiola crispa, 9 - Saxifraga oppositifolia - loose stand, 1 0 - 5 . oppositifolia - dense stand, 11 - Drepanodadus exannulatus - dense stand, 12 -range of Equisetum sp., 13 - Dicranum groenlandicum - loose spots, 14 - D. groenlandicum - range of dense stand, 15 - Cetraria sp. - dense growth, 16 - range of dense Gramineae stand, 17 - spot of Festuca sp., 18 - dry tundra dominated by Rhacomitrium lanuginosum, 19 - loose shrubby tundra, 20 - dense and luxuriant spots of shrubby tundra, 21 - top of hillock, 2 2 - 1957 nest, 23 - 1958 nest, 24 - l imit between loose and dense growth, 25 - l imi t of barren habitats. B. profile of hillock, 26 - l i ne of profile, 27 - profile

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