April 1995] ShortCommunications and Commentaries 521

DAWSON,D. G. 1981. Counting for a relative LAWTON,J. H. 1989. What is the relationship be- measure (index) of density. Pages 12-16 in Esti- tween population density and body size in ani- mating numbersof terrestrialbirds (C. J. Ralph mals? Oikos 55:429-434. and J. M. Scott, Eds.). Stud. Avian Biol. 6. PERRINS,C. g., AND T. R. BIRKHEAD. 1983. Avian INOUYE,D. W., W. A. CALDER,AND N.M. WASER. 1991. ecology. Blackie and Son, Glasgow. The effect of floral abundance on feeder censuses TERnORGI-I,J. 1989. Where have all the birds gone? of hummingbirdpopulations. Condor 93:279-285. Princeton Univ. Press,New Jersey. JOHNSTON,D. W., AND E. P. ODUM. 1956. Breeding WHITTAKER,R. H. 1970. Communities and ecosys- populationsin relation to plant succession tems. Macmillan, New York. on the Piedmontof Georgia.Ecology 37:50-62. JUANES,F. 1986. Populationdensity and body size Received4 February1994, accepted27 May 1994. in birds. Am. Nat. 128:921-929.

The Auk 112(2):521-523, 1995

Definitions for Migrant Birds:What is a Neotropical Migrant?

FLOYD E. HAYES Departmentof Biology, Union College, P.O. Box175, Port of Spain,

As a North American who has spent three years long agreed that most of (north of living in the TemperateZone of the Neotropics(Par- centralMexico) belongsto the Nearcticrealm, where- aguay), I often have wondered what the term "Neo- as , the Caribbean and all of South tropical migrant" refers to. Although some authors America (south to Tierra del Fuego) belong to the define a Neotropicalmigrant as any speciesof bird (e.g. Brown and Gibson 1983; see that migrateswithin the Neotropicalbiogeographical Fig. 1). In my mind, the two groupsof migrantscould realm (Stangel1992, Koford et al. 1994),the prevail- logically be referred to as: (1) "Nearctic migrants," ing view of a Neotropicalmigrant is a speciesthat which breedin temperateNorth Americaand migrate breedsin North Americaand spendsthe nonbreeding southward;and (2) "Neotropical migrants,"which seasonsouth of the Tropic of Cancer(e.g. Hagan and breed in temperateSouth America and migrate north- Johnston1992a, b, Finch and Stangel 1993), a view ward. But instead, North Americans have persisted which excludesaustral (southern)and intratropical in selectivelyapplying the term "Neotropical mi- migrants(Levey 1994).Levey (1994)adopted a broad- grants"to the speciesbreeding on the North Amer- er view of the term "Neotropical migrants" by in- ican continent and wintering to the south of the Tro- cluding the latter two groupsof migrantsin the def- pic of Cancer,which all but precludesthe useof the inition. I agree with Levey'sarguments that austral term for migrant speciesbreeding in temperateSouth and intratropicalmigrants need to be studiedfor both America. The use of this term in this context is so scientific and conservation reasons. However, by pervasivethat it frequently gracesthe titles of articles lurepingall of thesebirds into the samecategory, we in the major North American ornithologicaljournals, blur the already obscuredefinition of what a Neo- as well as the titles of two recently publishedsym- tropicalmigrant is and is not,which leavesus begging posium volumes (Hagan and Johnston 1992b, Finch for a more preciseset of termsand definitions for the and Stangel 1993). The term has been echoed re- various groups of migrants. peatedlyby conservationorganizations and alliances, In the , there are two fundamentally suchas Partners in Flight. As a consequence,workers distinct systemsof long-distancelatitudinal migra- suchas myself have been forced to use the term "aus- tion: (1) breeding birds in temperateNorth America tral migrants" in referenceto migrant speciesbreed- that migratesouthward to spendthe winter in warm- ing in (e.g. Chesser1994, Hayes et al. er climates, often in Central and South America; and 1994, Hayes 1995). (2) breeding birds in that As Levey(1994) and othershave proposed, we could migrate northward to spend the winter in warmer simply refer to all of thesemigrants as "Neotropical climates,but only rarely in North America. The dis- migrants," which is certainly logical becausethese tinctivenessof these two groups of migrants is ac- speciesall winter in the Neotropicsand their ances- centuatedby the timing of their seasonalcycles, which tors probablyevolved in the New World (e.g. are essentiallyhalf a year apart. Biogeographershave Brown and Gibson 1983). But then what definitions 522 ShortCommunications and Commentaries [Auk, Vol. 112

Fig. 1. The biogeographicalrealms of the world recognizedby mostbiogeographers (based on Brown and Gibson 1983).

shouldwe useto distinguishbetween the two major Ethiopianmigrant.--Any species of bird or population groupsof migrants?The majorgeographical distinc- of the speciesbreeding in Africathat regularlymi- tion betweenthese groups is where they breedrather gratesnorthward during the nonbreedingseason. than where they winter. Hagan and Johnston(1992a) Intratropicalmigrant.--Any speciesof bird or popu- and Levey (1994) referred to Neotropical migrants lation of the speciesthat breedsin the tropicsand breedingin North Americaas "Nearctic-Neotropical regularly migratesto another areaof the tropicson migrants," a preciseand accurateterm, but used the an annual basis. vagueterm "australmigrants" for speciesbreeding Nearcticmigrant.--Any species of bird or population in South America.These two terms are hardly com- of the speciesbreeding in North Americathat reg- parable.The term "austral migrants" could equally ularlymigrates southward during the nonbreeding apply to migrant speciesthat breed in Africa, Aus- season. tralia or Antartica, which are also in the Southern Neotropicalmigrant.--Any species of bird or popula- Hemisphere.Likewise, the term "boreal migrants" tion of the speciesbreeding in SouthAmerica that (northern migrants)could apply to migrant species regularly migrates northward during the non- breeding in either or both the Nearcticand Palearctic. breedingseason. To avoid confusionand ambiguity in the use of Palearcticmigrant.--Any speciesof bird or population these terms, I recommendthat a more preciseter- of the speciesbreeding in Europeor Asiathat reg- minologybe standardized.I proposethat the follow- ularly migratessouthward during the nonbreeding ing setof termsand definitionsbe adoptedby orni- season. thologists: These terms are not mutually exclusive.With this Altitudinalmigrant.--Any speciesof bird or popula- setof definitions,boreal migrants would includeboth tion of the speciesthat regularlymigrates from one Nearcticand Palearcticmigrants, whereas austral mi- altitude to another on an annual basis within a grantswould include Australian,Ethiopian, and Neo- biogeographicalrealm. tropical migrants.To give an example,the Peregrine Australmigrant.--Any speciesof bird or population Falcon(Falco peregrinus) as a specieswould fit mostof of the speciesbreeding in the Southern Hemi- these definitions; the North American populations spherethat regularlymigrates northward during would be consideredNearctic migrants as well as the nonbreeding season. boreal migrants,and the SouthAmerican populations Australianmigrant.--Any species of bird or population would be consideredNeotropical migrantsas well as of the speciesbreeding in Australiaor New Zealand austral migrants. that regularly migratesnorthward during the non- I realize that sucha drasticchange in the meaning breedingseason. of the term "Neotropical migrant" will be resisted Borealmigrant.--Any speciesof bird or population of initially and will take time to be accepted.However, the speciesbreeding in the Northern Hemisphere if the statusquo continues,we will continue to be that regularly migratessouthward during the non- confusedby a plethora of impreciseterms. Science breeding season. demands precision and logic in both our terms and April1995] ShortCommunications andCommentaries 523 definitions.In the caseof naming different groupsof An overview of the austral system.Bird Conserv. migrants, the names should be based on long-ac- Int. 4:91-107. ceptedterms and definitionsof biogeographicalrealms FINCH, D. M., AND P. W. STANGEL(Eds.). 1993. Status (e.g. Brown and Gibson 1983; Fig. 1). and managementof Neotropicalmigratory birds. Given the above definitions of Nearctic and Neo- U.S. Dep. Agric. ForestServ. Gen. Tech.Rep. RM- tropicalmigrants, how do we distinguishbetween (1) 229, Fort Collins, Colorado. Nearcticmigrants that migrate entirely within the HAGAN, J. M., III AND D. W. JOHNSTON. 1992a. In- Nearctic,and (2) thosethat migrateto the Neotropics? troduction. Pages1-3 in Ecologyand conserva- The distinctionbetween these two groupsof migrants tion of Neotropicalmigrant landbirds. Smithson- is important for both scientificand conservationrea- ian Institution Press,Washington, D.C. sons.I suggestthat the mostprecise terms, awkward HAG•a•, J. M., III AND D. W. JOHNSTON(Eds.). 1992b. asthey may be,are "Nearctic-Nearcticmigrants" and Ecologyand conservationof Neotropical migrant "Nearctic-Neotropicalmigrants," respectively. An al- landbirds. Smithsonian Institution Press, Wash- ternative(but lessprecise) set of termsmight be "tem- ington, D.C. perateNearctic migrants" and "tropicalNearctic mi- HAYES,F. E. 1995. Status, distribution and bioge- grants,"which couldbe simplifiedas "temperatemi- ographyof the birds of .Monogr. Field grants" and "tropical migrants," respectively.The Ornithol. No. 1. American Birding Association, sameprinciple of combiningterms could be usedfor ColoradoSprings, Colorado. speciesmigrating within or betweenother biogeo- HAYES,F. E., P. A. SCHARF,AND R. S. RIDGELY. 1994. graphical realms (e.g. Palearctic-Palearcticmigrants, Austral bird migrants in Paraguay.Condor 96: Palearctic-Ethiopianmigrants, Palearctic-Oriental mi- 83-97. grants,Palearctic-Australian migrants). KOFORD,R. R., J. B. DVNNING, C. A. RInIC,•D D. M. Acknowledgments.--Ithank J. M. Hagan III, D. W. FINCH. 1994. A glossaryfor avian conservation Johnston,D. J. Levey,and G. D. Schnellfor valuable biology. Wilson Bull. 106:121-137. commentsand suggestionson an earlier draft of this LEVEY,D.J. 1994. Why we shouldadopt a broader commentary. view of Neotropicalmigrants. Auk 111:233-236. STANGEL,P.W. 1992. Justwhat is a Neotropical mi- LITERATURE CITED grant?Partners in Flight Newsl.2(1):29. National and Wildlife Foundation, Washington, D.C. BROWN,J. H., ANDA. C. GInSON.1983. . C. V. Mosby, St. Louis, Missouri. Received9 August1994, accepted 27 January1995. CHESSER,R. T. 1994. Migration in South America: