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Evaluation of the Global Decline in the True Shrikes (Family Laniidae)

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Evaluation of the Global Decline in the True Shrikes (Family Laniidae) 228 ShortCommunications and Commentaries [Auk, Vol. 111 The Auk 111(1):228-233, 1994 CONSERVATION COMMENTARY Evaluation of the Global Decline in the True Shrikes (Family Laniidae) REUVEN YOSEF t ArchboldBiological Station, P.O. Box2057, Lake Placid, Florida 33852, USA The first International Shrike Symposiumwas held Shrike was found in 1975, and of the Northern Shrike at the Archbold Biological Station, Lake Placid, Flor- in 1982. In Switzerland, these two specieshave offi- ida, from 11-15 January 1993. The symposium was cially been declared extinct. attended by 71 participants from 23 countries(45% In Sweden, Olsson (1993) and Carlson (1993) have North America, 32%Europe, 21% Asia, and 2% Africa). attributed the decline (over 50% between 1970 and The most exciting participation was that of a strong 1990) of the Red-backed Shrike to the destruction and contingent of ornithologists from eastern Europe. In deterioration of suitable habitats. Olsson (1993) ob- this commentary I present the points stressedat the served a large reduction of pastures in the last two Symposiumand illustrate them with severalexamples decades,and considers the Swedish law requiring as presentedby the authors. planting of unused pastures and fallow lands with The Symposiumwas convened to focus attention conifers as unfavorable for shrikes. He also stated that on, evaluate, and possibly recommend methods to nitrogenousand acid-rainpollutants have influenced reverse the worldwide decline of shrike populations. vegetationcomposition and insectpopulations, both Many of the 30 speciesare declining, or have become of which in turn have affected shrikes negatively. In extinct locally. Studies have focused mainly on the the Swedish Bird Population Monitoring Program, five speciesfound closestto placeswhere ornithol- the numbers of Red-backed Shrikes declined from a ogists live: Northern/Great Grey Shrike (Laniusex- high index of 100 in 1975, to a low of 60 in 1981. cubitor);Red-backed Shrike (L. collurio);Loggerhead In southern Sweden, resultsof standardized, long- Shrike (L. ludovicianus);Lesser Grey Shrike (L. minor); term trapping of fall migrant Red-backedShrikes re- and Woodchat Shrike (L. senator). Other than anec- veal a continuing decline. A mean of 199 birds were dotal observations, little is known about the other 25 caught in the autumns of 1970sand 1980s,but de- species.A common theme of the Symposiumwas that creased to a low of 42 in 1991. The decline was first most long-term studiesof previously robust popula- noticed in the number of juvenile birds and later in tions of shrikes have documented drastic population adults, suggesting that the cause of the decline is declines,mostly in the late 20th century. For example, possiblya low reproductive rate. Several factorsmay Rothhaupt (1993) estimated that most central Euro- alter these rates.In a northern country like Sweden, pean countries have lost over 50% of their breeding climate and adverseweather can be major factorsde- populations of shrikes within the last 15 years. termining breeding success.In southeasternSweden, Regionalstatus and declines.--In post-war Switzer- Olsson monitored a population of about 10 pairs of land, shrike populations plummeted as human pop- Northern Shrikes for over 10 years and found the ulation increased from 4,700,000 in the 1950s to al- number of fledged young per brood to be 3.86 + SD most 6,500,000 today (Bassin 1993). Rapid economic of 2.0 in two bad years (1988, 1991), and 4.86 + 1.55 development paralleled this demographicgrowth. In in three good years (1989, 1990, 1992). In wet years, 1950, rural agricultural landscapeswere still domi- fledgling mortality was high and, consequently, re- nated by traditional livestock-breedingand cultiva- cruitment into the breeding population declined in tion methods, but extensive land-use changes have the following year. Further evidence of declining occurredfollowing the adoption of modern mecha- trends were presented by Przemyslaw Busse, who nized practices.These changesresulted in sweeping heads the "Operation Baltic" researchprogram that landscapemodifications that prevented populations monitors autumn migrants at three field stations on of resident Northern Shrikes from rebounding after the Baltic coastof Poland. Most speciesof small pas- the severe winters of 1962-1963, 1983, and 1985-1986. sefine migrants show a trend of declining numbers Breeding populations of all four speciesof shrikes (Busse1993). However, the greatestdecline is that of found primarily in rural areas have declined, and Northern Shrikes (regressioncoefficient for 30 years today in Switzerland only the Red-backedand Wood- = -5.12). A severe decline occurred at the end of the chat shrikes nest. The last nest of the Lesser Grey 1970s and in the 1980s when the average number trapped was only 4.2% that for the 1960s. The Red- backed Shrike exhibits a comparatively moderate de- ' Present address: International Ornithological cline (regressioncoefficient = 2.89), and levels for Center, P.Oi Box 774, Eilat 88000, Israel. 1984-1990 equal 44% of those for the 1960s. January1994] ShortCommunications andCommentaries 229 Data from the North American BreedingBird Sur- on private and public lands. Woods suspectedthat vey indicate a general decline in LoggerheadShrike habitat limitations may force shrikesto breed closer populationsduring 1966-1991 (Pete•ohn and Sauer together than they would otherwise. 1993). At the continental level, shrikes declined at an In Japan,Haas and Ogawa (1993) found that Brown average rate of 3.5% per year (average regional de- Shrikes (L. cristatus)were declining faster than Bull- clines3.1-4.4% per year). Thesedeclines were prev- headed Shrikes (L. bucephalus)in Hokkaido. The two alent in most states, provinces, and physiographic specieshave different breeding habitats,and the re- strata.Severe winter weather during 1976-1979 may sourcesused by BrownShrikes may be decliningmore have contributed to this decline in the eastern one- rapidly than those used by Bull-headedShrikes. Al- half of the continent. This combined with other fac- ternatively, the Brown Shrike alsomay be suffering torsduring the winter and breedingseasons that have high mortality on the wintering grounds or during beenimplicated in the rangewidedecline of this spe- migration, which the sedentary Bull-headed Shrike cies. Because recent studies have concluded that avoids. Brown Shrikes are caught in large numbers breedinghabitats are not limiting shrikepopulations, for food during their fall migration and on their win- and that reproductive successhas been normal, Pe- tering groundsin SoutheastAsia. Additionally, their terjohn and Sauer(1993) suggestedfactors within the wintering groundsare undergoing rapid habitat de- winter rangemay be limiting shrikepopulations. This struction(Severinghaus and Liang 1993). idea concurs with that of Temple (1993), who pos- Data from the previously inaccessibleEast Euro- tulated that many shrike populationsare below the pean countries indicate that avian censusingis not carrying capacityof their breeding habitat, and are widely practicedand was done mainly during 1982- limited primarily by the carrying capacityof their 1986,when ornithologistscollected data for the Atlas nonbreeding habitat. Conclusive evidence for this of BreedingBirds of Europe.Gorban and Bokotej(1993) theory has yet to be presented. from Ukraine, Malik (1993) from Czechoslovakia, and The idea that changes in breeding habitat have Kurlavicius (1993) from Lithuania reported that pop- causeddecline is supportedby someon-going studies ulations of Red-backed, Northern, and Lesser Grey in Alberta, where Collister and Henry (1993) found shrikesexhibit declining trends. that reductionof suitablebreeding habitat is an im- Stableor increasingpopulations.--Two exceptions to portant factor in the declinesof LoggerheadShrikes. the general pattern of declining regional populations In the prairie and aspenparklands of Alberta, 39%of came from Belarus and Poland. Nikiforov et al. (1993) unimproved pasture and up to 79% of presettlement observed an increase in the population of Northern grasslandswere lost between 1946 and 1986. The ma- Shrikes in southeastern Belarus, in areas that were jority were converted to cultivation. An examination evacuatedby humansfollowing the nuclear accident of occupied versus apparently suitable but unoccu- at Chernobyl in 1988. Since the Chernobyl incident, pied shrike territoriesin southeasternAlberta clearly shrikes have been observed breeding in abandoned demonstratedthat no suitable LoggerheadShrike villages and agricultural areas;however, biologists habitat was unoccupied. were unable to collect data on the ecological effects For southern Quebec, Laporte and Robert (1993) of radiationon the breedingpopulation. judged that the region is less suitablefor breeding Lorek (1993) reported a stablepopulation of North- Loggerhead Shrikes than it previously was because ern Shrikes in rural Poland. Comparedto neighbor- of the disappearanceof pastures,the larger areasun- ing countries,there is a lower rate of agricultural der cultivation, the predominance of corn fields, the mechanization and pesticide use in his study area, gradual removal of shelterbelts,and the return of which is attributed to the economicproblems of Pol- poor agricultural lands to forest. The mid-20th cen- ish farmers. He speculatedthat modern agricultural tury changefrom subsistencefarming to commercial practiceshave led to a reduction in large inverte- productionresulted in a
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