HYBRIDIZATION AND BREEDING SUCCESS OF COLLARED AND PIED FLYCATCHERS ON THE ISLAND OF GOTLAND

RAUNO V. ALATALO, LARS GUSTAFSSON,AND ARNE LUNDBERG Departmentof Zoology,Uppsala University, Box 561, S-75122 Uppsala,

ABSTRACT.--Twoclosely related Old World flycatchers,the Pied Flycatcher( hy- poleuca)and the (F. albicollis),are allopatricon most of the European mainland but have overlappingranges in centraland easternEurope and on the island of Gotland in the Baltic. On Gotland, the Collared Flycatcheris approximately 10 times as abundantas the Pied Flycatcher.The two specieshybridize (4% of all matings)at frequencies lessthan those predicted for random mating (13%). Mixed pairs produceas many offspring as pure Pied Flycatcherpairs and more offspring than Collared Flycatchers.The competence at courtshipand/or viability of offspring, however, is probably reduced, because fewer hybrids breed than would be expectedfrom the proportion of hybrid fledglings.

SPECIES are defined as intrafertile but non- onthe Baltic islands of Gotland and Oland (Fig. interhybridizing populations,and interspecif- 1). Sympatric populations hybridize to some ic hybrids are rarely encounteredin most sam- extent (L6hrl 1955, Alerstam et al. 1978). ples of under natural conditions. Collared and Pied flycatchersare closely re- Among , interspecifichybrids occur at a lated. Both are highly sex-dimorphicin plum- frequencyof one in about 50,000 (Mayr 1970). age. Malesof the two speciesare easilydistin- We assume that numerous isolating mecha- guishedfrom one another, the male Collared nisms owe their existenceto selectionagainst Flycatcherdiffering from the Pied Flycatcherin interspecific hybridization, which wastes having a white collar and rump. On the other genes.Yet, somebird speciespairs remain dis- hand, femalesare almost indistinguishablein tinct over much of their commonrange despite the field by plumage characters.The songsand hybridization in certain regions, perhaps es- alarm calls, however, are highly -spe- pecially those regions in which habitats have cific. recentlybecome greatly modified and/orwhere On the island of Gotland, where this study sympatry is recent (e.g. West 1962, Short 1969, was performed, the total populationsof Col- Mayr 1970, Gill 1980). Similarly, largely allo- lared and Pied flycatchershave recently been patric speciesmay hybridize in narrow zones estimated at 4,000 and 500 pairs, respectively of overlap, in which case it is sometimes a (Gustafssonand H6gstr6m in press).The near- matter of taste whether the two are best re- est CollaredFlycatcher population is found ap- garded as speciesor subspecies.While situa- proximately 600 km southeast of Gotland, tions of this kind are commonly described in while the Pied Flycatcherbreeds abundantly the literature, quantitative information about on the mainland of northern, central, and east- the rate of hybridization and the reproductive ern (see Fig. 1). Collared Flycatchers output of mixed, as opposed to pure, pairs is thus predominate in this peripheral, isolated almost always wanting. Here we report such area within the range of the more northerly details for a case of two European allospecies Pied Flycatcher. interbreedingin a zone of sympatry. In the present paper, we attempt to deter- The speciesinvolved are the Pied Flycatcher mine whether or not (1) birds mate assorta- (Ficedulahypoleuca) and the Collared Flycatch- er (F. albicollis).These Old World flycatchers tively and (2) breeding successof interspecific occuras allospecies(semispecies), with ranges pairs is reduced,as would be expectedfor true overlappingin centraland easternEurope and species.

285 The Auk 99: 285-291.April 1982 286 ALATALO,GUSTAFSSON, AND LUNDnEa6 [Auk, Vol. 99

• Pied flycatcher :.•!• Collaredflycatcher

0 500 1000 k m

Fig. 1. Breedingranges of Collaredand Pied Flycatchers(based on Alerstam et al. 1978, but modified from Creutz 1970 and Glowacinski 1974). The island of Gotland is encircled.

STUDY AREA AND METHODS Male hybrids can easily be identified from their vague whitish collars. In the hand, hybrid females Collared and Pied flycatchersare especially suit- can be distinguishedby the amount of white on their able for study becausethey use tree holes as nest sites. With nest boxes, one is able to control the neck feathers(see Svensson 1975). Collared Flycatch- er males were classifiedas old or yearlings on the whole population,because the birds seldomnest in basis of the color of all primary coverts (Svensson natural cavities when nest boxes are present. We 1975), while Pied Flycatchermales were aged from erecteda total of 435 nest boxesin two major forest the innermost primary covert (Alatalo et al. MS). habitats in southern Gotland (57ø10'N, 18ø20'E). In deciduouswoodlands the nest box density was 6/ha and in coniferous forest, 1.5 nest boxes/ha. The de- RESULTS ciduous woodlands are dominated by oak (Quercus robur)and ash (Fraxinusexcelsior), with a denselower Hybridizationfrequency.--The occupancy of layer of hazel (Corylusaveliana) and hawthorn(Cra- nest boxes and the breeding densities of dif- taegusspp.). The coniferousforest is dominatedby ferent pair combinations in the two habitats pine (Pinussylvestris), but birch(Betula pubescens) is are given in Table 1. The breeding density of also common. flycatcherswas 20 times higher in deciduous The arrival of the flycatcher males and their oc- than in coniferousforest, and many more nest cupationof territorieswere monitoredby censuses boxes remained unoccupiedin the latter hab- everysecond day. For each nest we recordedthe on- itat. The Collared Flycatcher was almost 30 set of laying, clutch size, hatching success,and times as abundant as the Pied Flycatcher in fledglingnumbers. We capturedand bandedall fe- deciduous forest, while in the coniferous area males and almost all males during the nestling pe- riod. In some caseswe did not succeedin capturing we found only three times as many Collared the male,because polygamous males seldom feed the Flycatchers.The proportionof mixed pairs was youngof their secondnests. The speciesidentity of much higher in coniferous forest than in de- these males was clear, however, from our census rec- ciduousforest (17% and 2.5%, respectively). ords. In addition, we observed four nests in which April1982] Hybridizationin Flycatchers 287

TABLE71. Breeding densities of Pied (PF)and Collared(CF) flycatchersand of mixed pairs in differenthabitats on the island of Gotland.

Percentage Size of occupancyby Density of breeding study Number Density of pairs/ha areas of nest Fly- All flycatcher Habitat (ha) boxes catchers species pairs/ha CF x CF CF x PF PF x PF Deciduous woodland 37 243 48.6 75.7 3.19 3.00 0.08 0.11 Coniferous woodland 116 192 9.9 24.0 0.16 0.10 0.03 0.03

one parentbird apparentlywas a hybrid; these habitat, so comparisonsmust take the time fac- pairs are not included in Table 1. tor into account. Our data are extensive for the If the individuals of the two speciesmated Collared Flycatcher, and we therefore use randomly, one would expect 13% of the pairs regressionequations for clutch size and fledg- to be mixed (Table2). The observedproportion ling numbers versus the laying date of this of mixed pairs was 4.4%, however, which de- species as a reference line. The regression viates significantly(X 2 = 7.66, P < 0.01) from equation for clutch size is: y = -0.078x + 6.77 random. Thus, there is an overrepresentation (SD = 0.66, n = 123), where x is laying date of intraspecificmatings, interbreedingoccur- (day 1 = 20 May). Pied Flycatchershad, on av- ring only in 36% of the number of casesex- erage,0.71 (SD = 0.84, n = 7) more eggsthan pectedif randommating is assumed.We may simultaneously laying Collared Flycatchers expect underrepresentationof mixed pairs, (Fig. 2). This differenceis significant(t = 2.70, simply becausethe frequenciesof occurrence P < 0.01). The clutch size of mixed pairs was of the two speciesare not identicalin the two intermediatebetween that of pure pairs of the habitats. In each habitat, however, the ob- two species(0.46 higher than for the Collared served number of mixed pairs was 29% (de- Flycatcher, SD = 0.65, n = 7, t = 1.81, ciduous: X2 = 5.11, P < 0.05) and 44% (conif- P < 0.10). erous:X 2 = 2.51,P > 0.10), lower than expected Hatching successof the flycatcherswas high, if random mating is assumed. In 5 of the 7 and no difference emerged among the pair mixed pairs (including 1 pair outside the main combinations(Table 3). The regressionline for study areas),the male was a CollaredFlycatch- fledgling numbers of the Collared Flycatcher er and the female a Pied Flycatcher.Moreover, decreasedmore rapidly with time than the line of all Pied Flycatchers,30% were involved in for clutch size (Fig. 3; regressionequation for interspecificmatings, whereas the correspond- number of fledglings: y = -0.128x + 6.43, ing figure for the CollaredFlycatcher was only SD = 1.71, n = 123). Early breeders presum- 2%. Of malesinvolved in interspecificmating, ably gained from an outbreakof caterpillars, 6 out of 7 (86%) were yearlings. For all intra- which levelled off in the second half of June. specificpairs this proportionwas lower (55%), but the differenceis not significant(Fisher ex- act, P = 0.12). Breedingsuccess.--Average clutch size and TABLE2. Observed and expected mating combina- tions of flycatchers. fledgling numbers of intra- and interspecific pairs are given in Table 3. We have combined Pure Pure the data from the two habitats, because we Collared Pied found no differencesin breeding successbe- Fly- Fly- tween habitats. Lundberg et al. (1981) found catcher catcher Mixed higher breedingsuccess for the Pied Flycatcher pairs pairs pairs in deciduous than in coniferous habitat, but Number found 123 7 6 the differencewas small. Laying date affects Percentagefound 90.4 5.1 4.4 breeding successmuch more profoundly than Percentageexpected 86.3 1.0 12.7 288 AL^•r^LO,GUS•r^FSSON, ^tad LUNDBERO [Auk, Vol. 99

•S4 i *%,0>%

ß M,xed pa,r

o Pied flycatcher

ß Mrxed parr

LAYING DATE

24 29 3 8 13 18 MAY JUNE

LAYING DATE Fig. 3. Number of fledglingsof Pied Flycatchers and of mixed pairs in relation to the regressionline for fledgling numbers versus laying date in the Col- Fig. 2. Clutch size of Pied Flycatchersand of lared Flycatcher. mixed pairs in relation to the regression line for clutch size versus laying date in the Collared Fly- catcher. to be significantusing the Mann-Whitney rank test (z = 2.17, P < 0.05). Because there is no differencein the mean laying date of the two Pied Flycatchersproduced, on average, 1.32 groups (Table 3), one could comparefledgling (SD = 1.32, n = 7) more fledglings than si- numbersdiscounting the laying date, in which multaneously breeding Collared Flycatchers case the difference is still significant (Mann- (Fig. 3). Unlike clutch-sizedistributions, the Whitney; z = 2.10, P < 0.05). Interspecific brood-size distributions clearly deviated from normal because of the total failure of some pairswere alsofo_und to producesignificantly more fledglings (y = 1.51, SD = 0.60, n = 7, broods.Therefore, t-tests of significancecould not be used, and, instead, we calculated for z = 2.84, P < 0.01) than simultaneously breeding Collared Flycatchers.No significant each Collared and Pied flycatchernest the de- difference was found between pure Pied Fly- viation in fledgling number from that to be catcher pairs and mixed pairs. expectedfrom the regressionline in Fig. 3. In this case,the regressionequation is used only DISCUSSION to standardizethe generaldecrease in breeding successwith season. Between-speciesdiffer- In the two flycatcherspecies, though mixed ences in terms of such deviations were found pairs occur, there is a clear preference for con-

TABLB3. Breeding data of Pied and Collared flycatchersand of mixed pairs.

Mean laying Clutch Hatched Species n date size SD eggs(%) Fledglings SD Collared Flycatcher 123 2 June 5.76 0.81 94.1 4.64 1.90 Pied Flycatcher 7 1 June 6.57 0.79 95.7 6.14 0.69 Mixed pairs 7 3 June 6.14 0.69 100 6.00 0.58 April1982] Hybridizationin Flycatchers 289 specific mates (Table 2). In two other cases of parent introgressionbetween severalallospe- allospecieshybridization, pairs alsomated as- cific pairs (for examples,see Anderson1977) sortatively [Gill and Murray 1972 (Vermivora implies that hybrids in many cases are not pinus/V. chrysoptera),Hoffman et al. 1978 (La- completelysterile. Brewer (1963;see also Ris- rus glaucescens/L.occidentalis)]. In the latter ing 1969)suggested that, in natural popula- case,quantitative data were provided. Because tions, hybrids of Parusatricapillus and P. car- only 25% of the Laruspairs were pure, the in- olinensisproduce less viable offspring. He cidenceof assortativemating was clearlylower found a very low fledglingsuccess in six nests than in this study. In contrast, Ingolfsson in an areaof sympatry.Examples of allospecific (1970) found that Larus hyperboreusand L. ar- pairsthat produce only F• hybridsare given by gentatusin Iceland mated randomly. Anderson (1977). In this study, 2 out of 4 pairs One would expect marked positive assorta- in which hybridswere involvedfailed to hatch rive mating if reproductivesuccess of interspe- their eggs,while 2 producedyoung (4 and 6, cific pairs or of hybrid offspringwere low and respectively).In one studyplot on the Swedish randommating if hybridizationdid not reduce mainland, (59ø50'N, 17ø40'E)where the Col- reproductivesuccess (Short 1972). Mixed pairs lared Flycatcheris absent,we found one hy- of Collared and Pied flycatchersproduced vi- brid male, which was paired with a Pied Fly- able offspring. In fact, mixed pairs produced catcherfemale. This pair raised four fledglings significantlymore offspringthan CollaredFly- from six eggslaid. L6hrl (1955)and Veps•l•i- catchers(Fig. 2), presumablybecause the Pied nen and J•rvinen (1977) each found a fertile, Flycatcherhas a largerclutch size than doesthe breeding, hybrid flycatchermale, but in the Collared Flycatcher(Fig. 2), and most of the latter casethe authorsmentioned the possibil- mixed pairs involved Pied Flycatcherfemales. ity that the broodcould have been adopted by What happens to the offspring of mixed fly- the hybrid male.Thus, in summary,flycatcher catcherpairs? Hybrids comprised6.4% of all hybridsare not fully sterilebut apparentlydo flycatcher fledglings but only 1.4% of the suffer from reduced fertility. Our data are too breedingadults (see also Alerstam et al. 1978). few to estimatethe viability and fertility of This implies reduced survival or incompetence hybrids accurately, but, because the two at courtship. It is not likely that hybrids are specieshave retained their specificcharacters less efficient foragers than pure individuals on Gotland so well, introgressioncan be as- (see Mayr 1970), because the two species are sumed to be slight. very similar in terms of their foraging habits Alerstamet al. (1978)suggested that hybrid- (Alerstam et al. 1978). On the other hand, the ization actsas an "agent of competition"be- two flycatcher species breeding on Gotland tween the two flycatcherspecies on Gotland. have largely different wintering areas(Moreau Becausethe Pied Flycatcheris less abundant, 1972), which may causeproblems for the hy- a greaterproportion of its populationwill suf- brids during migration. Hybrid males may be fer the risk of hybridization (see also Veps•- relativelyunsuccessful at courtship(Ficken and l•inen et al. 1975, Anderson 1977, Veps•l•inen Ficken 1968, Mayr 1970), becausetheir vocal- and J•rvinen 1977). The considerablerate of izations and courtship behavior may differ hybridization should prevent the Pied Fly- from the parental species.In fact, the songsof catcherfrom building up its population.The hybrid flycatchermales were clearly different hypothesisis based on the assumptionthat from the songsof the pure speciesand often hybrids are practically sterile. Mixed pairs includedspecies-specific elements of both the have high reproductivesuccess, but their hy- parental species.Also, hybrid femalevocaliza- brid offspringseem to be at a reproductivedis- tions differed from those of the parental advantage.Our datathus support the hypoth- species. esis of Alerstam et al. (1978) in that Offspring from interspecificmatings may be hybridizationmay help preventthe Pied Fly- fully fertile, may have reducedfertility, or may catcherfrom becoming established on Gotland. be sterile (Mayr 1970). For example, captive Conversely,hybridization may limit the ability Anas platyrhynchosand A. acuta procreated of the CollaredFlycatcher to colonizethe north fully fertile hybrids. Hoffman et al. (1978) and eastEuropean mainland, becausethe like- foundhigh breedingsuccess for hybridsof two lihood of hybridization will be very high for Larus species under natural conditions. Ap- a few immigrants(Veps•l•inen et al. 1975).An 290 ALATALO,GUSTAFSSON, AND LUNDBERG [Auk,Vol. 99 isolated island like Gotland would be easier to ACKNOWLEDGMENTS colonize than the mainland, if the Pied Fly- We are gratefulto T. Alerstam,F. B. Gill, O. Jar- catcher were established in Scandinavia before vinen, S. Ulfstrand, and K. Vepsalainen for valuable the CollaredFlycatcher. criticismof the manuscript.The work was supported Alerstam et al. (1978)proposed that the small by grants(to S. Ulfstrand)from the SwedishNatural Pied Flycatcherpopulation on Gotland proba- Science Research Council. bly is maintained by immigration from the surroundingmainland. We have examined this LITERATURE CITED possibility with the following simple model. ALERSTAM, T., B. EBENMAN, M. SYLV/•N, S. TAMM, We assumed a constant population level of & S. ULFSTRAND.1978. Hybridization as an 4,000 Collared Flycatcherpairs and 500 Pied agent of competition between two allospe- Flycatcherpairs (Gustafssonand H6gstr6m in cies: Ficedulaalbicollis and F. hypoleucaon the press),a hybridization frequencyequivalent to island of Gotland in the Baltic. Oikos 31: that found in the presentstudy, a 50% adult 326-331. survival rate to the next year (unpubl. data; see ANDœRSON,R. F. V. 1977. Ethologicalisolation and also Anderson 1977), and the same number of competitionof allospeciesin secondarycontact. offspring per pair of each speciessurviving to Amer. Natur. 111: 939-949. the next breeding season.Then, each year, 73 BREWER,R. 1963. Ecologicaland reproductive rela- tionships of Black-cappedand Carolina chicka- pairs (=15% of the total population) of Pied dees. Auk 80: 9-47. Flycatchershave to immigrate to Gotland to CREUTZ,G. 1970. Dringt der Halsbandschn•pper compensatefor the hybridization losses(if hy- nach Norden vor? Falke 10: 334-339. bridization leads to total reproductivefailure). FICKEN,M. S., & R. W. FICKEN.1968. Courtship of On the other hand, Pied Flycatchershad 32% Blue-winged Warblers and their hybrids. Wil- more fledglingsthan did the CollaredFlycatch- son Bull. 80: 161-172. ers (Table 3). If this difference were maintained GILL, F. B. 1980. Historical aspectsof hybridization until the next breeding, an immigrationrate of betweenBlue-winged and Golden-wingedwar- only 16 Pied Flycatcherpairs per year would blers. Auk 97: 1-18. be sufficient to retain a stable situation. Be- --, & B. G. MUm•A¾, JR. 1972. Discrimination cause huge numbers of Pied Flycatchersare behaviorand hybridizationof the Blue-winged and Golden-winged warblers. Evolution 26: captured and banded on Gotland during 282-293. spring migration (Rosvall 1979), an immigra- GLOWACINSKI,Z. 1974. Ekspansjamucholowki bi- tion of this modest magnitude may easily be aloszyjej,Ficedula albicollis (Temm.) w Europie achieved. õrodkowej.Przeglad Zool. 18: 471-484. The situation is complicated, however, by GUSTAFSSON,L., & S. H/JGSTR/JM.In press. Hur the fact that the Collared Flycatcheris socially mfinga ffiglar h•ckar pfi Gotland?Bl•cku. dominantover the Pied Flycatcher(L6hrl 1955). HOFFMAN, W., J. A. WIENSt • J. M. SCOTT. 1978. Studies on the Swedish mainland showed that Hybridizationbetween gulls (Larusglaucescens the Pied Flycatcherclearly prefers deciduous and L. occidentalis)in the PacificNorthwest. Auk 95: 441-458. forest (Lundberg et al. 1981), but the Collared INGOLFSSON,A. 1970. Hybridization of Glaucous Flycatcherseems to be able to monopolizethe Gulls Larus hyperboreusand Herring Gulls L. favorable deciduous habitats on Gotland and argentatusin Iceland. Ibis 112: 340-362. to relegate the Pied Flycatcherto suboptimal L6HRL, H. 1955. Beziehungenzwischen Halsband- habitats (Table 1). Even if there were no hy- und Trauerfliegenschn•pper( albicol- bridization, we believe that the Collared Fly- lis und M. hypoleuca)in demselbenBrutgebiet. catcherwould survive in its isolatednortherly Acta 11th Congr. Intern. Ornithol. 1954 (Basel): refuge. On the other hand, hybridization may 333-336. be the prime factor preventing the Collared LUNDBERG,A., g. V. ALATALO, A. CARLSON, & S. Flycatcherfrom establishinga population on ULFSTRAND.1981. Biometry, habitat distribu- the surroundingmainland. One can only spec- tion and breedingsuccess in the Pied Flycatcher Ficedula hypoleuca. Ornis Scandinavica 12: ulate about the origin of the presentstable dis- 68-79. tribution of the two species in Scandinavia, MAYR, E. 1970. speciesand evolution. Cam- but the isolated position of Gotland and the bridge, Massachusetts,Harvard Univ. Press. occurrenceof hybridization may well be of im- MOREAU, g. E. 1972. The Palaearctic-African bird portance. migration systems.London, AcademicPress. April1982] Hybridizationin Flycatchers 291

R•s•tac, J. D. 1969. A multivariate assessmentof in- SVEtaSSON,L. 1975. Identification guide to European terbreedingbetween the chickadees,Parus atri- . Stockholm, Naturhistoriska Riks- capillus and P. carolinensis. Syst. Zool. 17: museet. 160-169. VEPS•L•IIqEN, K., • O. J•RVINEN. 1977. Ein Bastard- ROSVALL,S. 1979. HalsbandsflugsnapparensFice- M•nnchen Halsband-Trauerschn•pper(Ficedula dula albicollisankomst till Gotland och (•land albicollisx F. hypoleuca)briitet in Finnland. J. v•ren 1979. Bl•cku 5: 73-78. Ornithol. 118: 436-437. SHORT,L. L. 1969. Taxonomic aspectsof avian hy- , K. KEYIq•S, & P. SALMINEIq. 1975. bridization. Auk 86:84-105. S;pelsiepotFicedula albicollis Hankoniemell• --. 1972. Hybridization, and avian 1971-74. Lintumies (Helsinki) 10: 118-122. evolution. Ann. Missouri Bot. Garden 59: WEst, D. A. 1962. Hybridization in grosbeaks 447-453. (Pheucticus)of the Great Plains. Auk 79: 339-424.

REVIEWERS FOR THE AUK, 1980-1981 TheAuk is fortunateto benefitfrom the servicesof many individuals who act as reviewersof manuscripts that are submitted. Their efforts are considerable,and their care and constructivenesscontinue to impress me as an Editor and as a sometimeauthor. The individuals listed below helped make publication of a journal with high scientificand scholarlystandards possible; my thanks to all of them. Individuals who have contributed reviews of two or more manuscriptsare indicated by an asterisk. Ian Abbott, David G. Ainley, JohnAlcock*, Thom- Fitch, JohnW. Fitzpatrick*, Brian K. Follett, Eric D. as Alerstam, Dean Amadon, Daniel W. Anderson, Forsman*,W. J. Francis,Leigh Fredrickson,Herbert Ted R. Anderson, C. Davison Ankney, Einar Arna- Friedmann, Carl Gans, C. Lee Gass*, A. J. Gaston, son, John C. Avise, Robert O. Bailey, Allan Baker, Sidney A. Gauthreaux, W. George, Frank B. Gill*, Myron C. Baker, Robert J. Baker, George S. Bakken, Robert E. Gill, P. D. Gingerich, BradleyM. Gottfried, Russell P. Balda, Thomas G. Balgooyen*, David F. Gilbert Gottlieb, Walter D. Graul, RussellGreenberg, Balph, Martha Balph*, Richard C. Banks*, Luis F. Paul J. Greenwood, T. C. Grubb, Jr., JosephA. Grzy- Baptista*,George F. Barrowdough*,George A. Bar- bowski, Svein Haftorn, Caldwell D. Hahn, F. Reed tholomew, Jr., ThomasS. Baskett,Range Bayer*, Jeff Hainsworth, William J. Hamilton, III, M.P. Harris, Baylis, Michael Beecher*, Colin Beer*, Marc Bekoff, Richard J. Harris, JeremyJ. Hatch, Helen Hays, Rob- Frank C. Bellrose, Jr.*, Louis B. Best*, T. R. Birkhead, ert E. Hegner, Dennis Heinemann*, Carl W. Helms*, CharlesR. Blem, Peter Boag,Walter Bock*, William Charles J. Henny*, Wayne Hoffman*, A. J. Hogan- R. P. Bourne,John H. Brackenbury,Richard A. Brad- Warburg, Richard T. Holmes, Dominique G. Hom- ley*, Eliot Brenowitz, I. Lehr Brisbin*, Pierce Brod- berger,John L. Hoogland*,Henry F. Howe*, Donald korb*, Richard G. B. Brown*, Charles J. Burke, M. F. Hoyt*, JohnP. Hubbard, George L. Hunt, Jr.*, R. Byrd, William A. Calder, Jr.*, Thomas Caraco, Cyn- Hutton, Jerome A. Jackson*, Frances C. James*, Dan- thia Carey*, Lynn F. Carpenter, Susan M. Case, iel H. Janzen*, Olli Jarvinen*, JosephR. Jehl, Jr.*, Graeme Caughley, Mary H. Clench, Charles T. Col- Paul A. Johnsgard*,Douglas H. Johnson*,David W. lins*, Michael Collopy, Edward F. Connor, Peter G. Johnston, Richard F. Johnston*, James R. Karr*, Janet Connors, Michael R. Conover*, Fred Cooke, John Kear, J. Allen Keast, Bretton W. Kent, Paul Kerlinger, Cooper, Kendall W. Corbin, Richard Cowie, Joel Lloyd F. Kiff, Lawrence Kilham, James R. King*, Cracraft*, Robert B. Craig, Richard D. Crawford, Warren B. King, Erwin E. Klaas*, Richard W. Knap- John Croxall, E. Curio, Thomas W. Custer, John Da- ton, Carl E. Korschgen, Gary Krapu*, John R. vis, David DeSante, Diane De Steven, Robert W. Krebs,DonaldE. Kroodsma,James A. Kushlan, Mary Dickerman, James J. Dinsmore, David S. Dobkin, K. LeCroy, Louis Lefebvre,Ross Lein*, Robert E. Richard A. Dolbeer, Hilary Dow, R. D. Drobney, Lemon*, K. Lessells,J. David Ligon*, C. D. Little- William H. Drury, Alfred M. Dufty, Jr., Arthur E. field*, Clare S. Lloyd, William J. Mader, Chris Marsh, Dunham, Erica H. Dunn*, Thomas J. Dwyer*, Eu- Carl D. Marti*, Dennis J. Martin, Elden W. Martin, gene Eisenmann,Phillip F. Elliott, John T. Emlen, L. D. Martin*, Steven Martindale, Barbara W. Mas- Robert Epting, Anthony J. Erskine, R. Michael Er- sey, Harold F. Mayfield*, Donald A. McCrimmon, win*, P. G. H. Evans,Roger M. Evans*,David Ewert, Jr., ChristopherMcGowan, Judith W. Mcintyre, Ann C. J. Feare*, J. Alan Feduccia, Peter Feinsinger, Mil- McNabb, A. H. Meier, Charles Meslow, L. Richard licent Ficken*, JamesS. Findley, Hans Fisher, Walter Mewaldt, David Miller*, Don E. Miller*, DouglasW.

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