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Home , Brown shrike, Great grey shrike, Lanius, Lesser grey shrike, Little owl, Loggerhead shrike

228 ShortCommunications and Commentaries [Auk, Vol. 111

The Auk 111(1):228-233, 1994

CONSERVATION COMMENTARY

Evaluation of the Global Decline in the True ( Laniidae)

REUVEN YOSEF t ArchboldBiological Station, P.O. Box2057, Lake Placid, Florida 33852, USA

The first International Symposiumwas held Shrike was found in 1975, and of the 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 , 32%, 21% , and 2% ). 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 . 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 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 Population Monitoring Program, five speciesfound closestto placeswhere ornithol- the numbers of Red-backed Shrikes declined from a ogists live: Northern/ (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); (L. minor); term trapping of fall migrant Red-backedShrikes re- and (L. senator). Other than anec- veal a continuing decline. A mean of 199 were dotal observations, little is known about the other 25 caught in the autumns of 1970sand 1980s,but de- .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 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 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 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 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 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 gradual decline in the num- brates,thus adverselyaffecting shrike populationsin ber of small farms. Marginal farmland reverted to mostof western Europe.This idea is corroboratedby forest or was urbanized, and mechanized corporate the findings of Esselink et al. (1993), who reported farms have increasedin size. Most corporate farms that large insectspecies are the mostendangered group are devoid of trees or shelterbelts. Thus, the mosaic of in the . Lorek (1993) stat- of small fields, used equally for pasture and crops, ed that global warming may have causedthe recent hasbeen replacedby large fieldsand, today,pastures mild winters in Poland with temperaturesrarely be- represent less than 15% of the total cultivated areas. low freezing,little precipitation,and abnormallyshort All these factorsmay have contributedto the decline periods of snow cover. As a result of warmer winters, of LoggerheadShrikes in southern Quebec. Northern Shrikes may have easier accessto Data presentedby Woods (1993) for Idaho provided and better winter survival. further evidence for the effects of human land-use Climaticfactors affecting shrike populations.--LeFranc practiceson shrike populations.Several territories of (1993) consideredclimate to be the most significant LoggerheadShrikes were destroyed by sagebrush- factorcontributing to continentwidedeclines of Less- eradicationpractices, and by horseand cattlegrazing er Grey Shrikes. He noted that low temperatures 230 ShortCommunications andCommentaries [Auk,Vol. 111

(<17øC)combined with heavy or persistentrains re- rious threats arise from drought in the eastern Sahel duce drasticallythe survival of young shrikesand Zone. Unlike mostother shrike species,which do not limit food availability for adults. LeFranc has ob- store much premigratory fat, but instead prey on served adult birds near starvation cannibalize their weakened passetinesduring migration, LesserGrey young in order to survive. Theseweather-related ef- Shrikes rely mostly on insectsas prey. In addition, fects are corroboratedby Barbara Diehi in Poland, their wintering area is much smaller than the breed- and Pinshow in Israel. Both observedthat cool ing range (about 1.50-1.75 million km 2 vs. 8 million and wet spring weather resulted in fewer shrike pairs km2) and, thus, adverseconditions on the wintering initiating breeding, probably becauseof a lack of in- grounds could be magnified because of their high prey. density (LeFranc 1993). Biologicalfactors affecting shrike populations.--Cade The decline of the Red-backedShrike is a good (1993) pointed out that most shrike species have a example of a scenarioin which governing factors rather high reproductive rate (i.e. they lay large causing drastic declines are not clear. In the 1850s, clutches, rear large broods compared to most other the Red-backedShrike bred throughout England av,d passerinespecies that nest in open cup nests, renest Wales. The population declined during the next 100 quickly and frequently after nest failure, and some- years,with a particularly rapid decline over the past times raise two or more broods per year). However, 40 years. In 1989, for the first time, no breeding was few breeding populationsof shrikesappear to reach recorded in England and Wales (Peakall 1993). Cli- the potential carrying capacityof their ranges,and maticchange has been the causemost frequently cited the shrikesare eitherpatchily distributed within large for the decline, and collecting and habitat de- tractsof apparentlysuitable habitat, or they arethinly structionmay have been important locally.The pos- dispersedover the available habitat. This suggests sibility of lossescaused by hunting in the Mediter- that environmentalvariables associated with nesting ranean countries was raised, but no data are available. habitatusually are not limiting, and that factorsfrom The limited information available does not suggest the nonbreeding period, either migration or winter- that competitionon the wintering ground is a serious ing, also should be investigated as causesof popu- problem.The reasonsfor the demiseof the Red-backed lation decline. Shrike in Britain remain unclear. Cadestressed the importanceof studyingmigratory Cade (1993) also suggestedseveral intrinsic char- routes by citing Walter's (1979) accountof acteristicsthat mayincrease the vulnerabilityof shrikes by the colonial nesting Eleonora'sFalcon (Falcoeleo- to . The first concernspatterns of dispersal. norae),which describeshow approximately 10,000 Shrikesapparently lack a strongly developed philo- breeding falconsand their young feed almost exclu- patry, and young birds do not breed near their natal sively on migrating birds that acrossthe Mediter- sites.Although adult malestend to have well-devel- raneanto Africa. Walter estimatedthat falconscaught opednest-site or nest-areatenacity, females frequent- one to two million migrants annually, out of a total ly do not (Yosef 1992). Females often change terri- migration that Moreau (1972) consideredto be on the torieswhen they renestin the sameseason, and have order of 5 billion birds in the 1960s.Consequently, little tendency to return to the same area from one the overall impact of the falcons' predation was as- year to the next, especiallyin migratory populations. sumed negligible. However, three speciesof shrikes These patternsof behavior could acceleratea popu- (L. collurio,L. minor,and L. senator)make up 15 to 20% lation'sdecline once a regionalpopulation has started of all birds taken (i.e. about 200,000-400,000 shrikes to break up into isolated demes as a result of habitat per year). At most sites, shrikes ranked as the first, fragmentation(Carlson 1993). A greater randomness second,or third most frequently taken species,de- is involved in finding a suitablebreeding area and a spite the fact that someof the other commonlytaken mate with this pattern of dispersalthan with a pattern Old World warblers and flycatchersnumbered in the involving strong philopatry and nest-sitetenacity in 100sof millions of individuals per species(Moreau both sexes. 1972). Unfortunately, no estimatesare available for A second intrinsic factor is their relatively poor the number of shrikes that cross the Mediterranean, flying ability, which increasestheir vulnerability to but the proportion taken exceedstheir relative abun- predators and collisions with vehicles (Cade 1993). dance in migration. Moreover, shrikes also have to Shrikes are fast, short-distancedashers and are very contend with Sooty Falcons(F. concolor)nesting at persistent,but not very maneuverable.Their long- the same time in the Sahara Desert and islands in the distance flight appears labored, which when com- Red Sea, as well as with numerous other bird pred- bined with a conspicuousplumage, makes them es- ators on their nonbreeding grounds in sub-Saharan pecially attractivetargets. An exampleof a high rate Africa (Cade 1993). of predation on shrikesis that by Little ( The Lesser Grey Shrike is another example of a noctua)on fledgling Northern Shrikes in Israel (Yosef speciesthat probably is affected on its wintering 1993a).We lack data on annual mortality of first-year grounds.They migratethrough the Middle East,where shrikes, which may be crucial for determining re- extensive hunting by humans is common. More se- cruitment rates in breeding populations. January1994] ShortCommunications andCommentaries 231

In Poland, Barbara Diehi studied Red-backed Shrikes rivated areas;intensive monocultures; disappearance for over 29 years on a 44-ha meadow plot, where of meadows,unfertilized ,and fallow lands; various stagesof forest successionform a mosaiclike decreaseof environmental diversity, due to the elim- landscape.During the study period (1964-1992), the ination of isolatedtrees, hedgesand thickets;drain- population of Red-backedShrikes went through dra- ing of marshes);(b) diminished diversity and quantity matic changes.Three periodswere distinguished:(1) of available prey causedby habitat alterations, and 14years of stability(1964-1977) with a maximummean use of fertilizers and (fewer large ; of about 8 pairs/10 ha; (2) 6 years of rapid decline elimination of small vertebrateprey); (c) climatic vari- (1978-1983);and (3) 9 yearsof partial recovery(1984- ation coupled with decreaseof prey populations;and 1992). Although Diehi (1993) found a positive asso- (d) decreasedenvironmental heterogenity (reducing ciation between successionalchanges in vegetation availability of optimal nest sites, shelters, and hunt- structureand shrike population density, nest preda- ing perches). tion, rather than habitat changes,accounted for the Thefuture.--The rapporteur, Uriel Safriel, summed rapid decline between 1978 and 1983. The decline up the Symposiumby stressingthat shrikesoffer ex- was initially observed around 1974; European Jays cellent opportunities to address basic problems in (Garrulusglandarius) and pine martens(M. martes)were ecologyand conservationbiology. Also, their behav- identified as the most important predators. ior of impaling prey in conspicuousplaces makes them Managementpossibilities.--Several researchers (D. van interesting subjectsfor studies in behavioral, evolu- Nieuwenhuyse in Belgium, G. Rothhaupt and M. tionary, and chemical . Safriel (1993) stressed Schonin Germany, R. Yosef in Israel and USA) have that, although many researchershave documented independently reachedthe conclusionby experimen- drastic declines and even local in breed- tation that structural features of shrike habitat exert ing populations, no one has establishedwhether the limiting effects(e.g. Yosef 1993b, Yosef and Grubb declines are within the bounds of potentially ex- 1992, 1993). Hunting perches, especially those asso- pected population dynamics.In addition, no one has ciated with rows, fences,and other elevated successfullycalculated "minimum viable population" structuresin agricultural landscapes,are often lack- sizesfor the various species.Safriel suggesteda mon- ing in areasotherwise apparently suitable for shrikes. itoring program wherein coordinated international Rothhaupt (1993) found that Northern Shrikes pre- collaboration would be the key to success. ferred perches 3 to 10 m high, with a minimum be- This monitoring program is now being imple- tween-perch distanceof 25 m. Thirteen of 24 inves- mented and researchersare collecting data on shrikes tigated habitats show perch densitiesbetween 5 and in a coordinated fashion. Hopefully, this internation- 15/ha. The averagedensity was 15.2perches/ha (range al effort will allow us to make recommendations to 1.7-35.5 perches/ha). According to Holzinger and reverse shrike declines and will be a model of co- Schon (1987), typical distancesbetween perchesare operation and conservationof other wildlife groups 15 to 20 m, and Bassin(1981) calculated an average that are also threatened by human actions. of 15.4 perches/ha. Acknowledgments.--TheAmerican Ornithologists' The importance of perchesto shrikes has been fur- Union contributed towards the participation of rep- ther illustrated by Carlson (1985), who found im- resentatives from Russia, Ukraine, Poland, and South proved detection of prey and nest predators from Africa. The International Council for Bird Preserva- higher perches by Red-backed Shrikes. In addition, tion-United StatesSection sponsoredrepresentatives Yosef and Grubb (1992) found that perch density af- from Czechoslovakia, Lithuania, and Poland. The fected nutritional condition of nonbreeding Logger- Kosciuszko Foundation, New York, partially spon- head Shrikes, and Yosef (1993b) further established sored three researchersfrom Poland. Warren B. King that Northern Shrike territory size and configuration partially sponsoredrepresentatives from France and could be manipulated by the introduction of appro- England.The ArchboldBiological Station contributed priate hunting perches. a minimum of 50%of the total costsof the Symposium. Conclusions.--The true shrikes are a rather uniform Fred E. Lohrer, Susan Earnst, Glen E. Woolfenden, group of 30 speciesof small- to medium-sized pas- and Terry Root improved earlier drafts of this report. setines that combine insectivorous and carnivorous modes of feeding. Becausedeclines in shrike popu- LITERATURE CITED lations in and North America have been con- current and becausewe have a desireto think globally BASSIN,P. 1981. Repartition e biotopes de la Pie- these days, it is perhaps tempting to look for a single grieche grise, Laniusexcubitor, dans le nord ouest causeor set of related causesunderlying all changes de la Suisse(Ajoie, Canton du Jura).Nos Oiseaux in shrike numbers. However, it is certain that the 36:1-20. causeswill prove to be multiple and varied for dif- B^SSIN, P. 1993. Status and trends of shrikes in Swit- ferent species.The following are probably the four zerland. Proc. Int. Shrike Symp. (R. Yosef and F. most important causesof declines in shrike popula- E. Lohrer, Eds.). Tech. Publ. West. Found. Vert. tions: (a) human land-use changes(expansion of cul- Zool. In press. 232 ShortCommunications and Commentaries [Auk, Vol. 111

BUSSE,P. 1993. Migration dynamics of Red-backed Shrike in Poland. Proc. Int. Shrike Symp. (R. Yos- and Great Grey shrikesin the Balticregion, 1961- ef and F. E. Lohrer, Eds.). Tech. Publ. West. Found. 1990. Proc. Int. Shrike Symp. (R. Yosef and F. E. Vert. Zool. In press. Lohrer, Eds.). Tech. Publ. West. Found. Vert. Zool. MALIK,J. 1993. Landuse changesand breeding of In press. Red-backed Shrikes in Czechoslovakia. Proc. Int. CADE,T.J. 1993. Shrikesas predators. Proc. Int. Shrike Shrike Symp. (R. Yosef and F. E. Lohrer, Eds.). Symp. (R. Yosef and F. E. Lohrer, Eds.). Tech. Tech. Publ. West. Found. Vert. Zool. In press. Publ. West. Found. Vert. Zool. In press. MOREAU,R.E. 1972. The Palearctic-African bird mi- CARLSON,g. 1985. Prey detection in the Red-backed gration systems.Academic Press, New York. Shrike (LaniuscoIlurio): An experimental study. NIKIFOROV, M. E., A. K. TISHECHKIN, AND B. V. Anim. Behav. 33:1243-1249. YAMINSKY. 1993. Status of shrikes in Belarus. CARLSON,g. 1993. Persistence of a Red-backed Shrike Proc.Int. Shrike Symp.(R. Yosefand F. E. Lohrer, populationin a patchylandscape. Proc. Int. Shrike Eds.). Tech. Publ. West. Found. Vert. Zool. In Symp. (R. Yosef and F. E. Lohrer, Eds.). Tech. press. Publ. West. Found. Vert. Zool. In press. OLSSON,V. 1993. The effectsof habitat changeson COLLISTER,D. M., AND J. D. HENRY. 1993. Preserva- the distributionand populationtrends of the Great tion of habitat in southeast- Grey and Red-backed shrikes in Sweden. Proc. ern Alberta. Proc.Int. Shrike Symp.(R. Yosefand Int. Shrike Symp. (R. Yosef and F. E. Lohrer, Eds.). F. E. Lohrer, Eds.). Tech. Publ. West. Found. Vert. Tech. Publ. West. Found. Vert. Zool. In press. Zool. In press. PEAKALL,D.B. 1993. The decline and fall of the Red- DIEHL, B. 1993. A long-term population study of backed Shrike in Britain. Proc. Int. Shrike Symp. Red-backed Shrikes in a heterogeneous and (R. Yosef and F. E. Lohrer, Eds.).Tech. Publ. West. changinghabitat. Proc. Int. Shrike Symp.(R. Yos- Found. Vert. Zool. In press. ef and F. E. Lohrer, Eds.).Tech. Publ. West. Found. PETERJOHN,B. G., ANDJ. R. SAUER.1993. Population Vert. Zool. In press. trends of the LoggerheadShrike from the North ESSELINK,H., M. GEERTSMA,J. KUPER,F. HUSTINGS,AND Americanbreeding bird survey.Proc. Int. Shrike H. MAN BERKEL.1993. Can peat-moor regener- Symp. (R. Yosef and F. E. Lohrer, Eds.). Tech. ation rescue the Red-backed Shrike in The Neth- Publ. West. Found. Vert. Zool. In press. erlands?Proc. Int. Shrike Symp. (R. Yosefand F. ROTHHAUPT,G. 1993. Current status and habitat of E. Lohrer, Eds.). Tech. Publ. West. Found. Vert. the Great Grey Shrike in Germany. Proc. Int. Zool. In press. Shrike Symp. (R. Yosef and F. E. Lohrer, Eds.). GORBAN, I., AND g. BOKOTEJ. 1993. Distribution of Tech. Publ. West. Found. Vert. Zool. In press. Laniidae in western Ukraine, and the breeding SAFRIEL,U. N. 1993. What's special about shrikes? biology of the Red-backedShrike. Proc.Int. Shrike Conclusions and recommendations. Proc. Int. Symp. (R. Yosef and F. E Lohrer, Eds.). Tech. Shrike Symp. (R. Yosef and F. E. Lohrer, Eds.). Publ. West. Found. Vert. Zool. In press. Tech. Publ. West. Found. Vert. Zool. In press. HAAS,C. g., ANDI. OGAWA. 1993. Population trends SEVERINGHAUS,L. L., AND C. T. LIANG. 1993. Food of Bull-headed and Brown shrikes in Hokkaido, and foraging behavior of Brown Shrike ( Japan.Proc. Int. Shrike Symp. (R. Yosefand F. E. cristatus).Proc. Int. Shrike Symp. (R. Yosef and Lohrer, Eds.). Tech. Publ. West. Found. Vert. Zool. F. E. Lohrer, Eds.).Tech. Publ. West. Found. Vert. In press. Zool. In press. HOLZINGER,J., ANDM. SCHON. 1987. Raubwurger-- TEMPLE,S.A. 1993. When and where are shrike pop- Laniusexcubitor. Pages 1195-1203 in Die Vogel Ba- ulationslimited? Proc.Int. Shrike Symp. (R. Yos- den-Wurttembergs (J. Holzinger, Ed.). Gefahr- ef and F. E. Lohrer, Eds.). Tech. Publ. West. Found. dung und Schutz, Teil 2, Karlsruhe, Germany. Vert. Zool. In press. KURLAVICIUS, P. 1993. Distribution of shrikes in WALTER,H. 1979. Eleonora's Falcon, adaptation to Lithuania. Proc. Int. Shrike Symp. (R. Yosef and prey and habitatin a socialraptor. Univ. Chicago F. E. Lohrer, Eds.). Tech. Publ. West. Found. Vert. Press,Chicago. Zool. In press. WOODS,C. P. 1993. Statusof LoggerheadShrikes in LAPORTE,P., AND M. ROBERT. 1993. The decline and the sagebrushhabitat of southwestIdaho. Proc. current statusof the LoggerheadShrike in Que- Int. Shrike Symp.(R. Yosefand F. E. Lohrer, Eds.). bec. Proc. Int. Shrike Symp. (R. Yosef and F. E. Tech. Publ. West. Found. Vert. Zool. In press. Lohrer, Eds.). Tech. Publ. West. Found. Vert. Zool. YOSEF,R. 1992. Male-biased breeding site fidelity in In press. a population of Northern Shrikes. Condor 94: LEFRANC,N. 1993. Decline and current status of the 1025-1027. LesserGrey Shrike in western Europe. Proc. Int. YOSEF,R. 1993a. Effectsof Little predation on Shrike Symp. (R. Yosef and F. E. Lohrer, Eds.). Northern Shrike postfledging success.Auk 110: Tech. Publ. West. Found. Vert. Zool. In press. 396-398. LOREK,G. 1993. Breeding statusof the Great Grey YOSEF,R. 1993b. Influence of observation posts on January1994] ShortCommunications andCommentaries 233

territory size of Northern Shrikes. Wilson Bull. YOSEF,R., AND T. C. GRuI313,JR. 1993. Effect of veg- 105:180-183. etation height on hunting behavior and diet of YOSEF,R., AND T. C. GRUBB,JR. 1992. Territory size LoggerheadShrikes. Condor 95:127-131. influencesnutritional condition in nonbreeding LoggerheadShrikes (Laniusludovicianus): A ptil- Received21 June1993, acceptedI July 1993. ochronologyapproach. Conserv. Biol. 6:447-449.

The Auk 111(1):233-236, 1994

Why We Should Adopt a BroaderView of Neotropical Migrants

DOUGLASJ. LEVEY Departmentof Zoology,University of Florida,Gainesville, Florida 32611, USA

Our worldview dictates our approach to science. 1992,Rappole and Tipton 1992).Thus, to understand Sometimes this influence is obvious; often it is not. the ecologyof Nearctic-Neotropicalmigrants we need In the latter case,we are at risk of intellectual stag- to understandthe dynamicsof tropical communities nation becauseof unconsciousbiases. Here I argue from which they came.This necessitates,for example, that the study of Neotropical migrant birds still suf- a broad view of interactions between resident and fers from largely unacknowledged temperate-zone migrant birds and how their populationsare linked biases.My purposeis to illustrate that, for both con- (Ricklefs 1992). servation-related and scientific reasons, we need to These points are not new. They crystallized at a adopt a broader, less traditional view of Neotropical 1977symposium (e.g. Rappoleand Warner 1980,Stiles migrants. 1980) and, although eloquently repeated since then The most widely held view of a Neotropical mi- (Ramos1988, Greenberg 1992a), have been ineffective grant is a speciesthat breeds north of the Tropic of in guiding currentresearch. An exceptionis work on Cancerand spendsthe nonbreedingseason to its south shorebirds,some of which integrates resident and (MacArthur 1959,Hagan and Johnston1992a, Stangel migrant ecologyand encompassesthe temporal dy- 1992). This definition excludesAustral and intratrop- namicsof tropical speciesassemblages (e.g. Van Dijk ical migrants,an exclusionthat is more than a prob- et al. 1990,Hockey et al. 1992).More recently, Young lem of semantics. and Morton (1994) took a broad view of Neotropical First, a narrow view of any topic usually definesa migrant landbirds. narrow scopeof study. It is not coincidentalthat re- Third, the narrow view of Neotropical migrants search on Neotropical migrants remains tightly fo- restrictsthe types of questionswe ask, which con- cusedon speciesthat fit the above definition (here- sequentlymay rob us of fresh insights.Tropical hab- after referred to as Nearctic-Neotropical migrants). itat requirements of Nearctic-Neotropicalmigrants Despiterecognition that Australand intratropicalmi- provide a clear example. Contrary to the notion of grantsare alsoNeotropical migrants(e.g. Hagan and tropical"stability," many tropicalbird communities Johnston 1992a), they are rarely studied as such. In are highly dynamic (Davis 1945, Beebe1947, Karr and fact, they are rarely studied at all (Loiselleand Blake Freemark 1983, Ramos 1988, Loiselle and Blake 1992). 1991,Chesser 1994, Powell and Bjork 1994).One rea- In CostaRica, for example,a large proportion of spe- son is a relative paucity of Neotropicalornithologists ciesshow evidence of seasonalmovements (Stiles 1983, (Short 1984). Another reason is that lack of awareness Levey and Stiles 1992). Presumably,many of these of these migrants may breed lack of interest. movementsare driven by resourcefluctuations (Loi- Second,the typical definition of a Neotropical mi- selle and Blake 1991, Rosselli 1994). Nearctic-Neo- grant disregards the evolutionary connection be- tropical migrants also experienceand likely respond tween intratropical and Nearctic-Neotropical mi- to spatialand temporal variation in their tropical re- grants. The former probably gave rise to the latter sourcebase. Indeed, many speciesdisplay movements and presently the two groups are practically indistin- in the tropicsthat are analogousto the seasonalmove- guishablein termsof ,diet, and habitat use ments made by closely related tropical residents (Dixon 1897, Mayr and Meise •930, Rappole et al. (Morton 1971, 1980, Levey and Stiles 1992). 1983,Ramos 1988). Their ecologicaland evolutionary Despite the dynamic nature of Neotropical bird parallelsare especiallyapparent while Nearctic-Neo- communities, most habitat studies on nonbreeding tropicalmigrants are in the tropics;they becomewell Nearctic-Neotropicalmigrants are short term. This integratedinto tropicalcommunities (Levey and Stiles practicemay reflect a temperate-zonebias, since the