Náttúrufræðingurinn

Volume

Náttúrufræðingurinn - 1999, Page 12

Náttúrufræðingurinn - 1999, Page 12
occupied territory, was used for calculations in subsequent years. Several people have hunted Ravens systeni- atically in the study area. We have the total catch of one of these hunters, Mr. Ingi Yngvason for 1981-1998 (in litt.). For other hunters we have information for the period 1981-1991 (Kristinn H. Skarphéðinsson etal. 1990, Wildlife Manage- ment Institute, in iitt.). The estimated size of the territorial popula- tion was 88 pairs in 1981 (60% occupancy), but only 58 pairs in 1998 (40% occupancy). Regres- sion of territorial population over years gave a highly significant negative trend (Fll7=24.5; P<0.001, Fig. 3). The decrease in the size of the territorial population amounts to 31% for 1981- 1998, or 2.1 % per annum. A number of territories are now deserted, i.e. have not been occupied for 5+ years. Deserted territories are found all over the study area, but are most common in the Mývatn area and the highlands east of Lake Mývatn (Fig. 2) where Ravens have been persecuted relentlessly during the past two decades. The percentage of occupied territories con- taining breeding pairs was on the average 85% (range 74-100%). Regression of this parameter over years gave no significant trend (Ft n=0.14; P=0.8). Nest success, i.e. the proportion of pairs breeding and fledging at least one young, was only measured in 1981-1985. On the aver- age 20% of all nesting attempts failed, the main cause being human interference. The estimated total production of lledglings in study area fell from 200 in 1981 to 120 in 1998, or40% (Table 1). A minimum of 100-200 Ravens were killed annually in the study area in 1981-1987, 200- 400 birds in 1988-1991, and c. 200 birds since 1992 (Table 2). The Raven catch increased c. 14% per annum in 1981-1991. From 1992 we only have data available from Mr. Ingi Yngvason, and his catch has been relatively con- stant during this period. This data shows clearly that for many years the Raven catch in the study area has been greater than the estimated young production of the local Raven population (Ta- bles 1 & 2). No studies have been done on whether the Raven hunt has benefited the waterfowl populations being protected with this action. On the other hand, a decrease in the Raven popu- lation could have negative effects on other organ- isms. The Gyrfalcon Falco rusticolus popula- tion in the study area uses mainly old Raven stick nests for breeding (52% of all nest sites, Cade et al. 1998). Some Gyrfalcon pairs now have problcms finding suitablc nest sites on their territories. All wild birds in Iceland are protected by law (Act no. 64/1994). According to the law the min- ister of environment can allow hunting birds for food or to prevent depredation, but this can only be done on a sustainable basis. The Raven has been regarded as a pest species, and there is no closed season. Our studies show that Raven hunting in Iceland is at present not in the spirit of the law; it is not a sustainable harvest. In our opinion this practise has to be terminated. One possibility would be to restrict hunting to areas where the Ravens cause damage, as at Eider colo- nies and other waterfowl colonies like at Lake Mývatn. Also, killing of Ravens should only be allowed during the time of year when the birds cause damage, e.g. the breeding season of the waterfowl. At other times the Raven should be protected. PÓST- OG NETFÖNG HÖFUNDA/AuTHORs' ADDRESS & E-MAIL María Harðardóttir ÓlafurK. Nielsen Náttúrufræðistofnun íslands / Institute of Natural History Hlemmur3 P.O. Box 5320 lS-125Reykjavík maria@ni.is okn@ni.is 154
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