J. Field Ornithol., 62(4):474-478

CHANGE IN DIET AND FORAGING BEHAVIOR OF THE ANTILLEAN IN AFTER HURRICANE HUGO

RAfJL A. PgREZ-RIVERA Departmentof Biology Universityof Puerto Rico HumacaoCampus Humacao, Puerto Rico 00661

Abstract.--From 1975 to 1990 the feeding habits of the Antillean Euphonia (Euphonia musica)were studiedin the Carite Forestlocated at Cayey, PuertoRico. The ,usually found in the canopyof mature rain forest,is considereda (Phoradendron spp.) specialist.The Antillean Euphonia is here reportedfeeding on eight additional speciesof and on arthropods.After Hurricane Hugo, the speciesshowed foraging and feeding flexibility such as searchingand gleaning for insectsfrom the undersideof in the mid-canopyand layer of the forest,and eatingvaried fooditems. Behavioralchanges may haveresulted from shortageof its usual food (mistletoe)in the forestcanopy as a result of major habitat disturbancefollowing the passageof the hurricane.

CAMBIO EN LA DIETA Y LA CONDUCTA DE.FORRAJEO DE EUPHONIA MUSICA EN PUERTO RICO DESPU•S DEL HURACAN HUGO Sinopsis.--De 1975 a 1990 se estudiaronlos hfibitosalimentarios del jilguero (Euphonia musica)en el Bosquede Carite localizadoen Cayey, Puerto Rico. La especie,tlpica del docelde bosquespluviales maduros, es considerada un especialistade la fruta de la capitana (Phoradendronspp.). En 6stetrabajo se informaal ave,alimentarse de otrasocho especies de plantasy de artr6podos.Luego del huracfinHugo, el ave mostr6gran fiexibilidaden suspatrones de forrajeoy alimentaci6ntales como el rebusquede insectosen la parte inferior de hojasde la capa media y arbustivadel bosque,e ingerir variadosalimentos. Los cambios en conductapueden set el resultadode la escacezde su alimentousual (capitana)en el docel del bosquecomo resultado de disturblosen el hfibitat posterioral pasodel huracfin.

Euphonias are consideredmistletoe (Phoradendronspp.) specialists (Danforth 1935, Faaborg 1985, Lack 1976, Skutch 1954, Snow 1981). In Puerto Rico the Antillean Euphonia (Euphoniamusica) is reportedto feed solelyon mistletoe(Biaggi 1983, Danforth 1936, Rivera-Gianchini and Mojica 1981, Wetmore 1916). Wetmore (1916), who examinedstom- ach contentsof 51 individuals,found exclusivelyseeds of severalspecies of mistletoe.In a paper apparentlyoverlooked by severalauthors, Sierra- Bracero(1973) reportedripe bananas(Musa sapienturn)in the diet of this small . The Antillean Euphonia is also considereda canopy speciesin rain forests(Danforth 1936, Dod 1978, Raffaele 1989, Wetmore and Swales 1931, Wunderle et al. 1987, per. ohs.);it is usuallyheard but difficultto observe.Herein, I report the speciesfeeding on different food items, includingarthropods, foraging at mid-canopyand shrublayer levels,and using previouslyundescribed feeding methods, particularly after Hurri- cane Hugo.

474 Vol.62, No. 4 Changein theDiet of the Antillean Euphonia [475

STUDY AREA AND METHODS The observations were made at the Carite Forest located in southeastern Puerto Rico in the municipalityof Cayey (Fig. 1). Carite is classifiedas a subtropicalmoist forest with an annual rainfall of 100-200 cm and temperaturesbetween 18 and 24øC (Ewell and Whitmore 1973). The forestis mainly a transitionalone, with many ecotones.Some of the forest's native vegetationhas been replacedby eucalyptus(Eucaliptus robustus) and pine (Pinus caribaea).The study area is locatedat an altitude of 400 m. The forest at this locationis a three-stratum formation. It has an open canopywith height averaging17-20 m in the overstory,7-9 m at mid-canopylevel, and 1-3 m in the relativelywell developedshrub level. The dominant vegetationat the study area includedtrees of bulletwood (Manilkara bidentata),candlewood (Dacryodes excelsa), sierra palm (Pres- toeamontana) and matchwood(Didimopanax morototoni). Tree-fall in the study area was minor following Hurricane Hugo. Nevertheless,most canopytrees sufferedbroken branchesand defoliation. From 1975 to 1988 while conductinga study on the feeding ecology of Puerto Rican , I made incidental observationson the feeding habitsof the euphonia.Observations were madefrom 0600 to 1800 hours. The samplingtechnique involved walking along an undeterminedpath in the studyarea until a was encountered.If the bird was observed foraging, information was recordedon its foraging height, behavior and food being consumed.Food items were collectedand taken to the labo- ratory for identification. taxonomyfollows Acevedo-Rodriguez and Woodbury (1985), Little and Wadsworth (1964), Little et al. (1988). Liogier and Martorell (1982) was used for English vernacularnames.

RESULTS AND DISCUSSION During a 13-yr period prior to Hurricane Hugo, I found that the Antillean Euphonia, although feeding mostly on mistletoe(93% of the foragingobservations), also includes other in its diet (Table 1). At Carite, 90% of the euphoniaswere observedforaging at canopy level, 1% in the mid-canopyand 9% in the shrublayer. In PuertoRico, euphoniasalso have been observedfeeding 1-2 m aboveground in dis- turbed second-growthforest (J. Wunderle, Jr., pers. comm.), and in xerophyticformations such as the GufinicaForest (pers.obs.). Also prior to Hugo, the only foragingtechnique I observedwas gleaning.Fruits were pluckedwhile euphoniaswere perched(98% of observations)or taken as they hovered.Food was mandibulatedbefore being swallowed. On 14 Oct. 1989, nearly a monthafter Hurricane Hugo, I visitedthe Carite Forestand observedsuch canopy inhabitants as Scaly-naped Pigeon (Columbasquamosa), Puerto Rican Vireo (Vireolatimeri), Stripe-headed Tanager (Spindaliszena) and Antillean Euphoniaforaging in the middle and lower strata of the forest. Similar behavior had been previously reportedin other Puerto Rican species(P6rez-Rivera and Bonilla 1982). 476] R.A. Pgrez-Rivera J.Field Ornithol. Autumn 1991

PUERTORICOCAYEY ,•

FIOURE1. Study area (cross-hatched).

But, two ,apparently a pair (the speciesis dichromatic),were observedfollowing very quietly (unusualin the species)a small flock of Bananaquits(Coerebaflaveola) and migratorywarblers (Dendroica caeru- lescens,D. tigrina and Parula americana)in their searchfor insectsin a pine stand. Later, the foraging flock movesinto the middle stratum of the hard-wood forest continuingtheir searchfor insects.The male eu- phonia was observedgleaning from the undersideof leavesof a rose- appletree (Eugeniajambos)in a mannersimilar to that of todies.A female euphonia,in companyof a Bananaquit, carefully examinedthe axils of a bromeliad(Guzmania sp.) and ingestedtwo small arthropods.At about noon, I interrupted another pair of euphoniasas they were feeding on the fruits of Rapaneacoriacea in the shrub layer. The two moved toward a small clump of of the vine, Marcgravia sintenissi.After a brief search,apparently looking for insects,the female ingestedparts of a . On 9 Jan. 1990, I again visitedthe Carite Forest. Although mosttrees

TABLE 1. Foraging observationsof Antillean Euphonia's in Carire Forest prior to Hur- ricane Hugo.

Plant species # individuals Dates Phoradendronspp. 270 Year-round since1975 Ficuslaevigata 9 Feb., Sep. 1983 Inga fagifolia 1 Aug. 1985 Didimopanaxmorototoni 1 Feb. 1986 Rapaneacoriacea 2 Apr. 1983 Miconia prasina 3 Oct. 1987 Mecraniumamigdalinum 2 Sep. 1986 Cassythafiliforrnis 1 Oct. 1985 Vol.62, No. 4 Changein theDiet of the Antillean Euphonia [477 had refoliated,some avian canopy species such as the Stripe-headedTan- ager and the Antillean Euphonia continued to feed in the lower and middle strata, respectively.From 0730 to 1330 hours, I observedsix euphoniasforaging but feedingsolely on mistletoe(19 obs.),although fruits of Rapaneaand flowersof Marcgraviawere available. Although a mistletoespecialist, the Antillean Euphonia feedson a varietyof fruits and on matteras do other speciesof the genus. Lack (1976) recordedthe JamaicanEuphonia (E. jamaica)feeding on flowersand invertebrates.Moermond and Denslow(1985) reportedE. violaceafeeding on 19 speciesof plants. Insectgleaning from undersidesby islandavifauna had beenpre- viouslyreported only for the Antilleantodies (Todus spp.) (Kepler 1977). The dietaryand behavioralshifts observed after Hurricane Hugo may haveresulted from a shortageof the euphonia'susual food (mistletoe) in the canopyof the forest.My observationsafter the stormconfirmed that the AntilleanEuphonia has evolved foraging and feedingplasticity. Craig (1989) has suggestedthat feedingflexibility, such as that shownin the euphoniasat Carite, may be an adaptationof islandspecies to periodic and major habitat disturbancessuch as hurricanes.Puerto Rico is affected by severehurricanes about every 10 yr (Wadsworthand Englerth1959), thusfacilitating the evolutionof suchplasticity in diet and foragingtech- niques.

ACKNOWLEDGMENTS

I thankJoseph Wunderle, Jr. andJohn Faaborg for theirsuggestions on improvingthe manuscript.Special gratitude goes to WayneJ. Arendtwho helpedgreatly to improvethis paper.

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