SHORT COMMUNICATIONS 251

971) suggestedthat this representeda “deceptive use of MORTON,E. S., M. S. GEITGEY,AND S. MCGRATH. 1978. song selectedto acquire male nest defense.” In this case, On bluebird “responsesto apparent female adultery.” as in the Black-headed Grosbeak, such “deceptive” be- Am. Nat. 112:968-971. havior would be adaptive since both parties would ulti- RITCHISON,G. 1980. Singingbehavior ofthe Black-head- mately benefit by the female’s singing and the male’s re- ed Grosbeak, Pheucticusmelanocephalus, with em- action to it, i.e., the bluebird nest is defended against a phasison the function of singingby females. Unpubl. possible predator and the eggsor young of the grosbeak Ph.D. diss., Utah State Univ., Logan. are not left unprotectedwhen the female leaves the nest. RITCHISON,G. 1983. The function of singing in female I thank Keith L. Dixon for his assistancein this study. Black-headedGrosbeaks: family-group maintenance. I also thank SusanSmith and an anonymousreviewer for Auk 100:105-116. helpful suggestionson the manuscript.This studywas sup- VAN TYNE, J., AND A. J. BERGER. 1976. Fundamentals ported by-grantsfrom The Frank M. Chapman Memorial of ornithology. Wiley and Sons, New York. Fund of The American Museum of Natural History and WESTON,J. G., JR. 1947. Breedingbehavior ofthe Black- from Sigma Xi. headed Grosbeak. Condor 49:54-73. LITERATURE CITED Department of Biology, UMC 53, Utah State University, DAWKINS,R., AND J. R. KREBS. 1978. Animal signals: Logan, Utah 84322. Present address:Department of Bi- information or manipulation?, p. 282-309. In J. R. ological Sciences, Eastern Kentucky University, Rich- Krebs and N. B. Davies [eds.], Behavioural ecology: mend, Kentucky 40475. Received 20 November 1981. an evolutionary approach. Sinauer, Sunderland,MA. Final acceptance10 January 1983.

Condor 85:251-252 0 The Cooper Ornithological Society 1983

HUMMINGBIRDS FEEDING FROM small resident populations of the above speciesof hum- mingbirds. EXUDATES ON DISEASED Both liquid and crystallized samples of exudate were SCRUB OAK collected for chemical analysis. Quantitative determina- tions were made on crystallizedmaterial, dissolvedin dis- tilled water, by paper or acrylamide thin layer chroma- PETER G. KEVAN tography as appropriate. Sugarswere identified using the methods of Baker and Baker (1979). Free amino acids SHERRENE D. ST. HELENS were measured by staining with ninhydrin (Yemm and Cocking 1955). The dansylation technique, described by AND Baker and Baker (1976) and Baker et al. (1978) was used IRENE BAKER to detect amino acids. Proteins were measured using bo- vine serum albumin as the standard and staining with bromphenol blue (Flores 1978). We also tested for the Hummingbirds are often thought to feed almost exclu- presenceof ascorbic acid with a technique that involves sively on floral nectars and occasionally hawk insects. the rapid bleaching of 2, 6-dichlorophenolindophenol Nevertheless,they are known to feed on fruits, from which (Nordmann and Nordmann 1969) for phenols by using they may remove exudedjuices (Lack 1976) and sap. For p-nitraniline and Folin reagent(Baker 1977) for alkaloids example, Ruby-throated Hummingbirds (Archilochuscol- and other compoundscontaining heterocyclic N, with the z&is) may feed from holes made by Yellow-bellied Sap- Dragendorff test (Harbome 1973, Baker 1977), and for suckers(iphyrapicus varius)in the trunks of paper birch lipids by staining with osmic acid and Sudan IV (Jensen trees (Betula papyrifera;Southwick and Southwick 1980). 1962). Edwards (1982) has pointed out that various humming- We also determined the pathogen responsible for the birds use secretionsof insects(coccids) living beneath the lesionsby having a specialistexamine thin sectionsof the bark of trees in Mexico, Colombia. and Brazil. diseasedtissue. In this note, we describea previously unknown food of hummingbirds: the exudate of pathogen-inducedlesions RESULTS AND DISCUSSION on plants. We discovered this on 16 August 1981 (about The lesionson the oaks were apparently producedby bac- 08:OO)as we watched at least six Broad-tailed Humming- teria. They contained no arthropods or fungi. Their exu- birds (Selasphorusplatycercus) and a male and a female date had a high ratio (1.117) of sucrose(to glucoseand Rufous Humminnbird_ (S. rufus)“, feeding.extensively on fructose),which is also characteristicof nectarsin flowers exudate dripping from swollen red lesions on the under- that are pollinated by hummingbirds (Baker and Baker, sides of twigs of Gambel oak (Quercusgambelil]. in press; Table 1). However, the level of amino acids in theexudate was higher than that of most nectarstaken by STUDY AREA AND METHODS humminabirds (Baker and Baker 1975). Manv such nec- The area where we made our observationshas been used tars contain phenols, as did the exudate (Tabie 1). previously for studiesof breeding birds (St. Helens 1981, Having seen many honeybees(Apis mellifera) feeding 1982). It is an 18.4-ha auadrat in the Bear Creek Nature at the lesions on other days (Kevan et al., in press), we Center, El Paso County,Colorado Springs,Colorado. The watched closely to see whether the hummingbirds were vegetation is dominated by Gambel oak and mountain hawking insectsrather than feeding on the exudate. They mahogany (Cercocarpusmontanus) and is typical of the were not; rather, they hovered beneath the terminal twigs dry foothills of the Front Range of the Rocky Mountains of the oaks and fed directly at the fluid. The male Rufous in Colorado. Affected oaks were common throughout the Hummingbird drove other hummingbirds off and, al- study area in 1981 and 1982. This area also supported though they remained in the area, their feedingbouts were 252 SHORT COMMUNICATIONS

TABLE 1. Chemical composition of exudate from bac- 140. In L. E. Gilbert and P. H. Raven [eds.], Animal terially-induced lesions on Quercusgambelli. and plant coevolution. Univ. of Texas Press,Austin. BAKER H. G., AND I. BAKER. 1979. Sugarratios in nectars.

Ingredient Concentration/presence m exudate Phytochem. Bull. 12:43-45. BAKER,H.G., AND I. BAKER. In press. Floral nectar sugar Sugar 872.6 &mg constituentsin relation to pollinator types. In C. E. Ratio of individual Jones and J. Little [eds.], Handbook of experimental sugars pollination. Van Nostrand, New York. Sucrose 0.528 BAKER.H. G.. P. A. OPLER,AND I. BAKER. 1978. A Glucose 0.220 cornparis& of the floral amino acid complements of Fructose 0.252 floral and extra-floral nectars.Bot. Gaz. 139:322-382. BAKER,I., AND H. G. BAKER. 1976. Analysis of amino Free amino acidsa 0.956 pg/rng acids in nectar. Phytochem. Bull. 9:4-7. Protein 0.932 &mg Ascorbic acid Present EDWARDS,E. P. 1982. Hummingbirds feeding on an ex- Phenols Present cretion produced by scale insects.Condor 84: 122. FLORES,R. 1978. A rapid and reproducible assay for Alkaloids and other quantitative estimation of proteins usingbromphenol compounds blue. Anal. Biochem. 88:605-6 11. containing heter- HARBORNE,J. B. 1973. Phytochemical methods: a guide acyclic N, Not detected to modem techniquesof plant analysis.Chapman and Lipid Not detected Hall, London.

a All 20 ammo acidswere present, including a-ammobutyric acid; JENSEN,W. A. 1962. Botanicalhistochemistry: principles mine, asparagine, and proline were most abundant. and practice. W. H. Freeman, San Francisco. KEVAN, P. G., S. ST. HELENS,AND I. BAKER. In press. Honeybees feeding from honeydew exudate of dis- consequentlybrief. Curiously, the birds were concentrated eased scrub oak in Colorado. J. Apic. Res. in a small area of about 50 X 50 m, despitethe much wider LACK,D. 1976. Island biology._. Univ. of California Press, availability of dripping infected trees. Becausethe exudate Berkeley. was exposed to the morning sun, it usually evaporated MAURIZIO,A. 1975. Honigtau-Honigtauhonig, p. 156- rapidly and crystallized(Kevan et al., in press):this would 200. In W. Kloft, A. Maurizio, and W. Kaeser [eds.], prevent hummingbirds from using it as a regular food Das Waldhonigbuch.Herkunft und Eigenschaftendes source(see Baker 1975, Pyke and Waser 1981). However, Waldhonigs. Ehrenwirth Verlag, Muchen. rain the night before our observations in 1981 and the MOWER,R. L., AND J. G. HANCOCK. 1975. Mechanism cool, damp, and cloudy morning kept the exudate watery of honeydew formation by Clavicepsspecies. Can. J. and available to the birds. No similar observations were Bot. 53:2826-2834. made in 1982, when the lesionswere brown and hard and NORDMANN,J., AND B. NORDMANN. 1969. Organicacids, no exudate was produced. p. 342-363. In I. Smith [ed.], Chromatographicand This exudateis a novel sourceof food for hummingbirds electrophoretictechniques. Vol. 1. Chromatography. but it is probably only a minor item in their diet. Through- 3d ed. William Heinemann, London. out most of the study period it was either very viscousor PYKE, G. H., AND N. M. WASER. 1981. The production had crystallized,and was thus in an inappropriate state to of dilute nectars by hummingbird and honeyeater be used as food. The exudate is generally nectar-like in flowers. Biotropica 13:260-270. chemical composition, rather than like the honeydew se- ST. HELENS,S. 1981. Forty-fourth breeding bird census. creted by insects(see Maurizio 1975) or fungal secretions No. 157. Gambel’s oak-Mountain mahogany wood- (see Mower and Hancock 1975). It is not regularly avail- land. Am. Birds 35:87. able from year to year, but given the opportunistic feeding ST. HELENS,S. 1982. Forty-fifth breeding bird census. habits of hummingbirds, it may be an important item No. 147. Gambel’s oak-Mountain mahogany wood- when customary foods are scarce. land. Am. Birds 36:86. We thank D. B. 0. Savile, Mycology, Biosystematics SOUTHWICK,E. A., AND A. K. SOUTHWICK.1980. Ener- ResearchInstitute, Agriculture Canada, for examining the geticsof feeding on tree sap by Ruby-throated Hum- lesionsand finding the bacteria. This work was supported mingbirds in Michigan. Am. Midl. Nat. 104:328-334. in part by grants from the National Science Foundation YEMM, E. M., AND E. C. COCKING. 1955. Determination (U.S.A.) to P. G. Kevan and H. G. Baker. of amino acids with ninhydrin. Analyst 80:208-2 13. LITERATURE CITED Deoartment of Environmental Biology, University of BAKER,H. G. 1975. Sugarconcentrations in nectarsfrom Guelph, Guelpi, Ontario NI G 2 WI, Cynada. Addressif hummingbird flowers. Biotropica 7:37-4 1. secondauthor: P. 0. Box 6053, ColoradoSprings, Colo- BAKER,H. G. 1977. Non-sugar chemical constituentsof rado 80934. Addressof third author: Department of Bot- nectar. Apidologie 8:349-356. any, Universityof California, Berkeley,California 94720. BAKER,H. G., AND I. BAKER. 1975. Studies of nectar- Received 26 February 1982. Final acceptance8 November constitutionand pollinator-plant coevolution, p. 1OO- 1982.