Interisland Variation in Blood Drinking by Galapagos Mockingbirds

July1987] ShortCommunications 517

Interisland Variation in Blood Drinking by GalhpagosMockingbirds

ROBERTL. CURRYAND DAVID J. ANDERSON• Departmentof Biology,The University of Michigan,Ann Arbor,Michigan 48109-1048 USA

Few speciesof birds are known to feed on the blood many sea lions gave birth. Up to four birds at a time of living animals, and the occurrenceof this behavior fed from each placenta,eating tissuesand drinking in populations of the Sharp-beaked Ground-Finch from pools of blood on the rocks. (Geospizadifficilis) on Wolf and Darwin islands, Ga- We saw Espafiola mockingbirds drink blood from l•tpagos,has becomenotorious (Bowman and Billeb living marine iguanas on four different occasions,all 1965, KiSsterand KiSster1983, Schluter and Grant 1984). in 1984, in sectionsof rocky coastwhere iguanaswere It is lesswidely recognized,however, that Galhpagos abundant. In each case the bird fed from a small hole mockingbirds (Nesomimusspp.) on some islands also in the iguana's tail until the victim moved into a drink blood from living hosts. Occasional blood protected position. Nesomimusmacdonaldz may create drinking by mockingbirds on two islands was men- these wounds incidentally while tearing off and eat- tioned previously, but without details on the fre- ing ticks or skin from marine iguanas, as sometimes quency or distribution of the trait (Bowman and Car- occurswhen N. parvuluspecks ticks from land iguanas ter 1971, Christian 1980). on Santa Fe (Christian 1980). On Espafiola25% of 100 We observed blood drinking during studies of iguanasexamined had wounds like those from which mockingbirdcooperative breeding (Curry) and booby we saw mockingbirds drink blood. In contrast, we breeding biology (Anderson) between 1981 and 1985. found no such wounds on 100 iguanas at Isla Lobos Four endemic,allopatric mockingbird species inhabit and Cerro Brujo,San Crist6bal,where we did not see the archipelago (Swarth 1931). We studied N. mac- mockingbirdsglean ticksor drink blood. We alsosaw donaldi on Espafiola;N. trifasciatus,the Floreana several N. macdonaldidrink blood from the ground (Charles Island) Mockingbird, on Champion and Gardner-by-Floreana;N. melanotis,the San Crist6bal (ChathamIsland) Mockingbird, on SanCrist•bal; and N. parvulus,the Gal•pagosMockingbird, on Darwin, Fernandina, Genovesa, Isabela, Santa Cruz, Santa Fe, Santiago, and Wolf. We studied color-banded birds on Genovesa(1981-1985), Champion (1981-1985), Es- pafiola (1984-1985), and San Crist•bal (1984). On the other islands we observedunmarked birds during brief visits. Mockingbirds(N. macdonaldi)on Espafiolaforaged in all habitats, eating fruit and both terrestrial and marine arthropods;the diet of mockingbirdson other islands is similar (Grant and Grant 1979, Curry un- publ. data). We observed Espafiola mockingbirds drinking blood from living sea lions (Zalophuscali- fornianus),marine iguanas (Amblyrhynchussubcrista- tus), and nestling Masked Boobies(Sula dactylatra) in two locationsnear Punta Cevallos.Mockingbirds also twice attempted to drink blood from superficial wounds on the legs of field investigators. On 27 December1983 a woundedbull sealion pulled out on an Espafiolabeach after receiving severe lac- erationsin its genital area during a fight with another male. Between 1400 and dusk at 1800 six banded mockingbirdsdrank blood directly from the sealion's woundswhile it lay on the beach.The bull left during the night, and the birds pecked at blood on the sand the next day. Mockingbirds also frequently obtained bloodfrom sealion placentasin one coastalarea where Fig. 1. Mockingbird (Nesomimus macdonaldi) drinking blood from a conspicuouswound in the • Present address:Department of Biology, Univer- neck of a living Masked Booby(Sula dactylatra) nest- sity of Pennsylvania, Philadelphia, Pennsylvania ling on Isla Espafiola,Gal•tpagos, while standingon 19104 USA. the victim's head. 518 ShortCommunications [Auk,Vol. 104

T^I•LE1. Blooddrinking and associatedbehavior among Gal•pagos mockingbird (Nesomimus spp.) populations.Blood drinking includes only bloodtaken from living hosts;iguana pecking includes mockingbirds gleaningticks or skin;carrion feeding includes only vertebratesources. Host organismsare abbreviatedas follows:marine iguanas(MI), land iguanas(LI), lava lizardsor geckos(LG), seabirds(SB), sea lions (SL), tortoises(T), and goats (G). Behavior not observed on well-studied islands is indicated by a dash.Mockingbird behaviorremains poorly known on islandsindicated by a questionmark. Sourcesof observationsare denoted by footnotes.

Iguana Species Island Blooddrinking pecking Carrionfeeding N. macdonaldi Espafiolaa,b'c'a'• SL, SB,MI MI, LG LG, MI, SB,G N. melanotis San Crist6bab f,• -- MI -- N. trifasciatus Championa -- -- LG, SL, SB Gardner-by-Floreana•,h ? ? SB N. parvulus Baltra i ? ? LI Darwin a _ ? ? Fernandina •'b,• -- MI, LI LI Genovesa a -- -- SB Isabela a'• ? ? LG Marchena a,k -- MI LG Seymour ? ? ? Pinta k -- ? LG R•bida ? ? ? Santa Cruz a,b -- -- LG Santa Fea,b,i,l MI, LI MI, LI MI, G, SL Santiagoa'm ? ? T Wolf a -- ? ?

This study. Bowman and Carter (1971). Amadon (1966). Carpenter (1966). ' Gifford (1919). Venables (1940). Bowman (pers. comm.). Harris (1968). Beebe(1924); populationnow extinct. Christian (1980). Schluter(pers. comm.). A. Laurie (pers. comm.). Darwin (1841). after a Gal•pagosHawk (Buteogalapagoensis) killed with their bills. Parental boobies also defended their and removedan iguana(see Bowman and Carter 1971). chicksand occasionallymay have killed blooddrink- Espafiolamockingbirds obtained blood more fre- ers:we found the bodiesof four mockingbirds,in- quentlyfrom seabirdsthan from sealions or iguanas. cluding a bandedindividual that previouslydrank We observedmockingbirds drinking blood from 9 bloodfrom a boobynestling, next to nestscontaining different MaskedBooby nestlings (25-50 daysold) in boobychicks. During longintervals when boobypar- 1984 and from another 22 in 1985, in an area at Punta entsleft the nestto forage,blood drinking by mock- Cevallosof roughly 300 boobynests. Espafiola mock- ingbirdswas interruptedonly when nonparental ingbirds also attack Blue-footed Boobies(S. nebouxii; boobies resumed their assaults on the chicks. Attack- Nelson 1968)and Waved Albatross(Diomedea irrorata) ing mockingbirdsgathered around each victim and chicks(S. Harcourt pers. comm.), but we sawno mock- attempted to perch on its back or head to eat tissue ingbirds drink blood from thesespecies. Most, if not and drink blood (Fig. 1). In a few caseswe sawonly all, of the 31 victimshad been assaultedby nonpar- one mockingbirddrink blood from a chick,but usu- ental adult Masked Boobies,resulting in abrasions ally several did so (mean minimum number of and lacerationson the chicks'necks, heads, rumps, feeders = 4.3 + 5.1 SD, n = 28). As each victim's and wings. We do not know why theseassaults (Nel- conditiondeteriorated and it becameincreasingly un- son 1978: 385) occurred,but the wounds clearly at- responsive,more blood drinkersjoined in. In one case tracted mockingbirds.[Finches (G. difficilis)on Wolf at least35 mockingbirdsfed froma singlebooby nest- feedfrom boobynestlings wounded in the sameway ling just before it died. Most victims died within 24 (K/Ssterand K/Sster1983).] When firstattacked, booby h of the onsetof blooddrinking, usually after their chicksdeterred mockingbirds temporarily by jabbing vertebralcolumns and spinalcords were exposed. July 1987] ShortCommunications 519

At least 38% of the 55 mockingbirds resident at tions about the origin of these unusual traits. It is not Punta Cevallosdrank boobyblood one or more times, surprisingthat someGal•pagos mockingbirds should and some individuals alternated between two victims drink bloodbecause all forageopportunistically (Beebe in a single day. Birds from other parts of the island 1924, Amadon 1966, Bowman and Carter 1971, Grant where seabirds did not nest also drank blood from and Grant 1979,Curry 1986),in commonwith the few boobies at Punta Cevallos; three of the banded N. other speciesof blood-drinking birds (Bowman and macdonaldiwe saw drinking blood held territories 2 Billeb 1965).This factor does not explain why blood km away. drinking is restrictedto just a few populations. Our data are insufficientto determine what pro- Unlike egg eating by Gal•pagos mockingbirds portion of the diet of mockingbirdson Espaf•olacon- (Bowman and Carter 1971), there is no simple cor- sistsof blood. The fact that mockingbirdsavidly ex- respondencebetween blood drinking and ecological ploit all availablesources of blood suggeststhat blood setting,mockingbird morphology, or the distribution is a preferred food. Blood drinking may occurpre- of hostsamong the islands.Espafiola, Santa Fe, and dominantlyduring dry seasonswhen other foodsare Genovesa are small, low, and arid islands where scarce.The blood drinking we observedtook place mockingbirds are among the longest-billed forms during dry periods in both 1984 and 1985. Blood (Swarth 1931).Blood drinking occurson Espafiolaand drinking was lessfrequent under wetter conditions Santa Fe but not on Genovesa. Potential sources, in- in 1986 (Anderson pers. obs.). cluding sealions (Eibl-Eibesfeldt1984a), iguanas (Eibl- Information available about other islands indicates Eibesfeldt1984b), and nesting seabirds(Harris 1973), that there is considerableinterisland variability in occur virtually throughout the archipelago. Addi- blood drinking and related behavior among Gal•- tional factorsmust be invoked to explain why blood pagosmockingbird populations (Table 1). In Table 1 drinking is not common to all arid-island popula- we have listed all known recordsof blood drinking tions. from living hosts; we also include observations of Variation in social behavior among Gal•pagos mockingbirds removing ticks or skin from iguanas mockingbird populations may account partially for ("iguana pecking") or feeding on carrion, because the distributionof blood drinking. If specializedfeed- mostof the few otherknown blood-eatingbird species ing techniques,including blood drinking, are learned feed on ectoparasitesor carrion,or both (Bowmanand (Bowman and Billeb 1965, Christian 1980), such traits Billeb 1965). After Espafiola,blood drinking occurs may becomeestablished in socially complex popu- mostfrequently on SantaFe, where mockingbirds(N. lationsin which opportunitiesfor learning occurfre- parvulus)occasionally drink blood from land iguanas quently, as suggestedfor tick pecking in Aphelocoma (Conolophuspallidus; Christian 1980) and from marine coerulescens(Baber and Morris 1980, Isenhart and iguanaswounded by hawksor sharks(A. Lauriepers. DeSante 1985). Gal•pagos mockingbirds have com- comm.).Blood drinking is not known to occurin any plex social organizations that include group territo- other Gal•pagosmockingbird population. Nesomimus riality and cooperativebreeding (Hatch 1966, Grant parvuluson Genovesahas not beenseen drinking blood and Grant 1979,Kinnaird and Grant 1982,Curry 1987). from any living hosts,though mockingbirds have been With some variation these factors correlate with blood studiedintensively there since1978 using field meth- drinking. Mockingbirds in coastalareas of Espafiola, odsidentical to thosewe usedon Espafiola(Grant and where blood drinking is mostfrequent, live in large Grant 1979, Kinnaird and Grant 1982, Curry 1985, groups (up to 17 birds) at high density (9-16 birds/ pers.obs.). Anderson saw finches(G. difficilis),but no ha); on SantaCrist6bal, where blood drinking is not mockingbirds,drink blood from seabirdson Wolf and known to occur,mockingbirds live in much smaller Darwin in 1981. We found no evidence of blood groups(2-3 birds)at lower density(less than 1 bird/ drinking in N. parvuluson Santiago,Isabela, Fernan- ha) (Curry 1987). However, mockingbirds live in dina, or SantaCruz. Mockingbirds (N. trifasciatus)on moderatelylarge groups(averaging 3-4 birds) at high Champion feed on carrion, and on Gardner-by-Flo- density (4 birds/ha) on Champion and Genovesa reana they occasionallykill seabird chicks (Harris (Curry 1987) but do not drink blood, so social com- 1968),but we did not observeiguana pecking or blood plexity alone does not fully accountfor the distri- drinking on either islet. No blood drinking or carrion bution of blood drinking. feeding has been reported in N. melanotis.The birds We suggest that interisland variation in blood we studiedat three locationson SanCrist6bal (Playa drinkingmay result from differencesin the frequency Baquerizo,Cerro Brujo,E1 Junco) foraged arboreally of opportunitiesto sampleblood, which could arise and did not attempt to feed from iguanasor seabirds, in at leasttwo ways. First, blood should be more often but Bowman (pers. comm.) saw N. melanotispecking availableto mockingbirdson islandswhere Gal•pa- ticks from marine iguanasat another location (Punta gos Hawks kill or wound large prey such as iguanas Pitt). or seabirds than on islands without hawks. A role for The occurrenceof blood drinking and associated hawks in mockingbirdblood drinking is supported behaviorby mockingbirdson someislands, combined by the observationthat hawks are residenton Espa- with their apparent absenceon others, raisesques- fiola and SantaFe, where mockingbirdsdrink blood, 520 ShortCommunications [Auk,Vol. 104 but hawks are absentfrom Genovesa,Champion, Dar- Park Service. We thank Superintendent Miguel Ci- win, R•bida, SanCrist(•bal, Santa Cruz, Seymour,and fuentes for his support. Wolf (Harris 1973), islands where mockingbirds are not known to drink blood. Blood drinking by mock- LITERATURE CITED ingbirdscould be expectedon other islandswith resident Gal•pagos Hawks (Isabela, Fernandina, Mar- AMADON,D. 1966. Insular adaptive radiation among chena, Pinta, and Santiago), but foraging patterns in birds.Pp. 18-30 in The Gal•pagos(R. I. Bowman, these mockingbirdpopulations are not sufficiently Ed.). Berkeley, Univ. California Press. well known to testthis prediction. Mockingbirdsalso BABER,D. W., & J. G. MORRIS. 1980. Florida Scrub mightbe exposedto bloodfrom smaller animals killed Jaysforaging from feral hogs. Auk 97: 202. by Short-earedOwls (Asiofiammeus) or CommonBarn- BEEBE,W. 1924. Gal•pagos:world's end. New York, Owls (Tyto alba).The distribution of neither of these Putnam's Sons. predators, however, coincides with the pattern of BOWMAN,R. I., & S. L. BILLEB.1965. Blood-eatingin blooddrinking amongmockingbird populations. Asio a Gal•pagosfinch. Living Bird 4: 29-44. inhabits all principal islands,including thosewhere , & A. CARTER.1971. Egg-peckingbehavior in mockingbirdsdo and do not drink blood, and Tytois Galfipagosmockingbirds. Living Bird 10:243-270. absent from Espafiola, where blood drinking by CARPENTER,C. C. 1966. The marine iguana of the mockingbirds is most conspicuous. Gal•pagosIslands: its behaviorand ecology.Proc. Mockingbirds could be differentially exposedto California Acad. Sci., Ser. 4, 34: 329-375. blood through iguana pecking. Mockingbirds that CHRISTIAN,K.A. 1980. Cleaning/feeding symbiosis glean ectoparasitesfrom iguanas would have fre- between birds and reptiles of the Gal•pagosIs- quent opportunities to sample blood. Generalized lands: new observations of inter-island variabil- blood drinking may have derived from a protocoop- ity. Auk 97: 887-889. erative associationbetween mockingbirds and igua- CURRY,R. L. 1985. Breeding and survival of Gal•- nas (Christian 1980, Isenhart and DeSante 1985; see pagosmockingbirds during E1Nifio. Pp. 449-471 also Bowman and Billeb 1965). Consistent with this in E1 Nifio en las Islas Gal•pagos:el evento de hypothesis,mockingbirds most frequently drink blood 1982-1983 (G. Robinson and E. del Pino, Eds.). on islandswhere they also peck at iguanas(Table 1), Quito, Ecuador, Fundaci6n Charles Darwin para although mockingbirdshave been seen pecking at las Islas Gal•pagos. iguanason two other islands (Fernandinaand San 1986. Gal•pagos mockingbird kleptopara- Crist6bal)where no bloodfeeding has been reported. sitizes centipede. Condor 88: 119-120. Furthermore,the hypothesisfails to explain why the 1987. Evolution and ecologyof cooperative tendency to peck at iguanasvaries among mocking- breeding in Gal•pagosmockingbirds (Nesomimus bird populations. spp.).Ph.D. dissertation,Ann Arbor, Univ. Mich- Unless additional factors can account for variation igan. in iguana pecking by mockingbirds,the hypothesis DARWIN,C. R. (Ed.). 1841. Zoology of the voyageof that hawks indirectly influence mockingbird blood H. M. S. Beagle,under the commandof Captain drinking is better supportedby the information avail- FitzRoy, R. N., during the years 1832-1836. Part able. It remainspossible, however, that blood drink- III: Birds. London, Smith Elder & Co. ing arosesimply by chancein just two populations. EIBL-EIBESFELDT,I. 1984a. The Gal•pagosseals. Part Regardlessof which explanationfor the distribution 1, Natural historyof the Gal•pagossea lion (Zal- of blood drinking is correct, N. macdonaldion Espa- ophuscalifornianus wollebaecki, Sivertsen). Pp. 207- fiola has evolved on exceptionaltendency to exploit 214 in Key environments: Gal•pagos (R. Perry, blood from any available source. Ed.). New York, Pergamon. This researchwas carried out in conjunctionwith 1984b. The large iguanas of the Gal•pagos P. R. Grant'sstudies of Gal•pagosland birds;we thank Islands. Pp. 157-173 in Key environments: Ga- him for help throughout the study and for comments lfipagos(R. Perry, Ed.). New York, Pergamon. on an earlier draft. We thank R. I. Bowman for con- GIFFORD,E. W. 1919. Field notes on the land birds structive criticism and his unpublished observation of the Gal•pagos Islands and of Cocos Island, of iguana pecking on San Crist•bal. R. Brubaker,B. Costa Rica. Proc. California Acad. Sci. 2, Ser. 4: Coffman, S. Curry, S. Forther, L. Hamilton, M. Itur- 189-258. ralde, S. Stoleson,and S. Webb provided field assis- GRANT,P. R., & N. GRANT. 1979. Breeding and feed- tance. The Charles Darwin ResearchStation helped ing of Gal•pagosMockingbirds, Nesomimuspar- with logistics,and World Wildlife Fund-US,the Frank vulus. Auk 96: 723-736. M. Chapman Memorial Fund, the George D. Harris HARRIS,M.P. 1968. Egg-eatingby Galfipagosmock- Foundation,Sigma Xi, and the University of Michi- ingbirds. Condor 70: 269-270. gan contributedfinancial support. Permission for this 1973. The Gal•pagosavifauna. Condor 75: study was grantedby the Direcci6n General de De- 265-278. sarolloForestal, Ecuador, and the Gal•pagosNational HATCH,J.H. 1966. Collective territories in Gal•pa- July 1987] ShortCommunications 521

gosmockingbirds, with noteson other behavior. ß 1978. The Sulidae. Oxford, Aberdeen Univ. Wilson Bull. 78: 198-206. Press. ISENHART, F. R., 8t D. F. DESANTE. 1985. Observations SCHLUTER,D., 8t P. R. GRANTß1984. Ecologicalcor- of ScrubJays cleaning ectoparasitesfrom black- relatesof morphologicalevolution in a Darwin's tailed deer. Condor 87: 145-147. finch, Geospizadifficilis. Evolution 38: 856-869. KINNAIRD,M. F., & P. R. GRANT. 1982ß Cooperative SWARTH,H.S. 1931. The avifaunaof the Gal•pagos breeding in the GalfipagosMockingbird, Neso- Islands.Occ. Pap. California Acad. Sci. 18: 1-299. mimusparvulus. Behav. Ecol. Sociobiol. 10: 65-73. VENABLES,L. S. V. 1940. Nesting behaviourof the K•SSTER,F., & H. K•SSTER.1983. Twelve daysamong Gal•pagosMockingbird. Ibis 82: 629-639. the "vampire finches"of Wolf Island. Not. Ga- lfipagos38: 4-10. Received8 August1986, accepted 16 January1987. NELSON,B. 1968. Gal•pagos,islands of birds. New York, William Morrow and Co.

Further Evidence of Long-term Pair Bonds in Ducks of the Genus Bucephala

GILLES GAUTHIER 1 Departmentof Zoology,University of BritishColumbia, Vancouver, British Columbia V6T 1W5, Canada

In holarcticducks, pair formation occursduring the all cases the mates of marked males were marked. winter or the springmigration, or both,and pair bonds Retentionof saddleswas poor after 2 yr, but the leg are seasonal,usually lasting until the onsetof incu- bandsenabled me to identify individualsup to at least bationby the female(McKinney 1986).Because males 4 yr. desert their mates during incubation and leave the Pair 1 consisted of the same individuals in 1983 and breeding grounds for molting, it has been thought 1984.This pair wasnot seenon the studyarea in 1985, that new pair bondsare formed every year and that but female 1 returned in 1986 with a new mate. From repairingwith the samemate does not occur(Rowley 1982 to 1984, and again in 1986, female 1 nested suc- 1983, McKinney 1986). In dabbling ducks, marking cessfullyin the sametree cavity,and her matealways males on the breeding grounds has confirmed that defendedthe sameterritory, located on the pond clos- long-term pair bonds (>1 yr) do not occur (Poston est to her nest. The reasons for her absence in 1.985 1974, Blohm 1978), although exceptionsexist (e.g. are unknown as both the cavity and territory were Dwyer et al. 1973). In seaducks,however, there is unoccupied. evidencethat pairing with the same individual for Pair 2 involved the same male and female for at more than one breeding seasonmay be a common least three consecutive seasons. Female 2 failed to occurrence.Savard (1985a) recently reported that in hatcha clutchin all yearsand changednest sites every Barrow'sGoldeneye (Bucephalaislandica) the return year. The pair changedponds from 1983to 1984but rates of adult males and females to the breeding not in 1985.In 1986 male 2 returned unpaired for a groundswere similar (66% vs. 76%), and that several fourth year to the samepond. His former mate did pairs reunited in subsequentyears. I now present not return to the studyarea. For muchof the nesting evidence that male Buffleheads (B. albeola) are also seasonhe remainedon the samepond, where he joined philopatricto their breedingarea and that pair bonds transient groups of nonbreeders and performed can reform in subsequentyears. courtshipdisplays to unpaired females. The studywas conductedin the CaribooParkland Pair 3 nestedsuccessfully in 1983but was not seen of British Columbia.In 1983 I captured3 male Buf- subsequentlyon the studyarea. Male 3, however,was fieheadsusing a mirror trap (Savard 1985b),whereas known to be alive in the following year becausehe 66 femaleswere trapped on the nest between 1982 was resightedon the wintering area near San Diego, and 1985. All birds were marked individually with California,in December1984 (T. Meyer pers.comm.). color-coded nasal saddles and a set of color bands. In Two of the three markedpairs, therefore, remained intact for 2 yr and one of them for a third year. Buf- fieheadsare highly territorial during the breeding season(Gauthier 1987),and philopatry of femalesto Presentaddress: D•partement de Biologie, Uni- the territoryis high (Erskine1961, Gauthier in prep.). versit• Laval,Ste. Foy, QuebecG1K 7P4, Canada. My resultsshow that philopatrymay alsobe strong