October1982] ShortCommunications 791

ß 1981. Microgeographicvariation in the song tories of North American Cardinals,grosbeaks, of the SageSparrow. Condor 83: 113-119. buntings,towhees, finches, sparrows, and allies row: spatialand random aspects.Wilson Bull. (O. L. Austin, Jr., Ed.). U.S. Natl. Mus. Bull. 92: 425-438. 237, part 2. ROBB•S, C. S. 1970. Recommendationsfor an in- W•E•s, J. A. 1969. An approachto the study of ternational standard for a mapping method in ecologicalrelationships among grassland birds. bird census work. Audubon Field Notes 24: 723- Ornithol. Monogr. 8. 726. Received18 January 1982, accepted 12 April 1982. WAL•CI•SHAW,L. H. 1968. Spizellapusilla pusilla: EasternField Sparrow. Pp. 1217-1235in Life his-

Does the Woodcock Bob or Rock--and Why?

WILLIAM H. MARSHALL 7248 OakmontDrive, SantaRosa, California 95405 USA

Details of the behavior of the American Woodcock worm from the surface,probed deeply to pull out a (Philohelaminor), other than thoseof the mating dis- large worm, or extractedan insectfrom under a leaf. play, are little known. Undisturbedbirds fly only for The head was well forward and held slightly to one brief periods in twilight and are almostalways well side with the tip of the bill 3 cm or less above the concealedwhile on the ground. Woodcockmay be- surface.Sometimes progress was brokenby repeated comeconspicuous, however, when they feed in open rocking in one place, and, lessoften, the bird stood areasduring daylight hours. motionless for several minutes. On two such occasions,I observed the repetitious On 4 April 1974,I watchedanother bird for 45 rain body motionsof undisturbedbirds from a largewin- in the samearea during the middle of the afternoon. dow in my home in St. Paul, Minnesota. The birds Although the ground had been bare for more than a moved about a flat-to-gently-slopinglawn and ad- week, 15-20 cm of fresh wet snow had fallen the jacent areas coveredby tall sparsestaghorn sumac previous afternoonand evening. This bird walked (Rhus typhina) and small box elder (Acer negundo) slowly on top of the snow with the same rocking that had no branches below 1-2 m. The area was 12- motions.The next morning I trackedit for about 300 45 m below the window and 25-50 m away. I used rn and found no sign of probing, although it had either 7 x 50 binocularsor a 20x spottingscope, and, stoppedat the baseof severaloak trees,where a few as there was a high, thin overcastand all observa- grassstems or dry leavesprotruded above the snow. tions were between 0630 and 1730, the light condi- The early literature on woodcockbehavior is thor- tions were very good. oughly reviewed by Pettingill (1936),who also pre- One bird, observed for a total of 8 h between 29 sentedhis own observationson bobbing. He cited March and 1 April 1978, actively fed on the lawn, Christy (1931: 14) who noted "the well-known tee- with a few excursions to the leaf litter under the tering movement of the woodcock'sbody." Sheldon shrubs. There was some old snow nearby but none (1%7: 84) quoted Glascow(1958) as noting that "these in this area. I probed the saturatedsoil with an alu- woodcockwalked a few stepsin a (rumba-like man- minum rod and found that the frost line varied from ner)" on a dry lawn in east Texas. de Forges (1975: 5 to 20 cm in depth. As the bird slowlywalked about, 425) reported that a nesting Eurasian Woodcock its head and neck remained on a level plane, but its (Scolopaxrusticola) bobbed "now and again" while body wasalmost continually moving back and forth, feeding away from the nest. Worth (1976)gave a de- best describedas "rocking." A line betweenthe neck tailed descriptionof body bobbing by a woodcock and dorsal feathers was obvious, because, while the on a lawn in New Jersey.Severinghaus (1978: 748) body moved, the head did not. One foot was lifted said of the Eurasian Woodcock in Taiwan that "Feed- high then placeddown ahead with the weight on it; ing bouts were prefacedby a bobbing behavior in the other foot was lifted so that only the tips of the which the body moved (seesawed)while its head toes were in contactwith the ground. This repeti- and legs remained stationary." tious movementstopped when the bird pickeda small Four explanationsof the bobbing have been ad- vanced.Pettingill (1936:269) believed"that bobbing is a nervousaction resultingfrom fear or suspicion." • MinnesotaAgricultural Experiment Station, Scientific Journal Se- The several observations cited above, however, were ries Paper No. 11,891. of undisturbed birds, as were mine. Further, the re- 792 ShortCommunications [Auk, Vol. 99 action of the 1978 bird to a disturbanceby squirrels termed "rocking" to distinguish it from the "bob- and rabbits was to stand at the "alert" posture (Mor- bing motions" of the Dipper (Cinclusmexicanus) (Pe- genweck 1978: 50). terson 1961:173) or the "teetersup and down" of the Worth (1976: 374) dismissed the idea of mimicry Spotted Sandpiper (Actitismacularia) (Peterson 1961: "of leavesbeing movedby a breeze"in his statement 81). These terms describequite different motions. that "when a breezewas not blowing the woodcock's R. O. Morgenweckand M. W. Weller reviewed the movements made it conspicuous."During one pe- manuscript,and the latter participatedduring about riod of my observations,the movementof deadleaves an hour of observation in 1978. in the wind was erraticand "jerky" in sharpcontrast to the bird's rhythmic repetitiousrocking. Worth (1976:375) also thought that Woodcock"may CHRISTY,B. H. 1931. Woodcocksin a dry season. teeter and bob to mimic prevailing shadows" and Cardinal 111: 13-14. asks, "Was it consequentlyperforming some auto- vœ Foacœs,G. 1975. Behavior of an incubating matic act more appropriate to a shadowed dappled woodcock. Brit. Birds 68: 421-428. ambience?"All of my observationswere made under GLAscow, L. L. 1958. Contributions to the knowl- overcast skies when there were no shadows. Cer- edge of the ecologyof the AmericanWoodcock tainly, both birds were very conspicuousas they (Philohelaminor) on the winteringrange in Lou- rocked, whether, in descendingorder of conspicu- isiana. UnpublishedPh.D. dissertation,College ousness,they were on snow, lawn, or in leaf litter. Station, Texas, Texas A&M Univ. Christy (1931: 14) thought that worms were "lo- Moacœtqwœc•c,R. M. 1978. Crepuscularbehavior cated by the sense of feeling, through its feet." I of American Woodcock (Philohelaminor Gmelin) would suggest that a minute movement of earth- and summer and fall habitat utilization by fe- worms close to the surface (or insects in leaf litter), males in northeasternMinnesota. Unpublished in responseto the slight changesin pressure from Ph.D. dissertation, Minneapolis, Minnesota, the rocking bird's foot, allows the woodcockto detect Univ. Minnesota. them by sight or perhapsby an infinitesimalsound. PETœaSO•,R. T. 1961. A field guide to western Sheldon (1967: 36) states that "When food is on the birds, 2nd Ed. Boston,Houghton Mifflin Co. surfaceof the ground, there is no doubt that the vi- PœTXt•tLL, O. S., Ja. 1936. The American Wood- sualability of the woodcockcomes into play." In my cock (Philohela minor). Mem. Boston Soc. Nat. observations,and thoseof Christy and Glascow,the Hist. 9:169-391. worms were in saturated soils, hence undoubtedly Sœvœat•Avs, S.R. 1978. Diurnal behavior of an close to the surface. EurasianWoodcock (Scolopax rusticola). Auk 95: PerhapsPettingill's "nervous actionresulting from 748. fear or suspicion," however, or Worth's "automatic S•œLvo•, W. G. 1967. The book of the American act" are applicable to the bird that rocked on the woodcock. Amherst, Massachusetts, Univ. Mas- snow, where there certainly were no vulnerable sachusetts Press. earthworms or insects. Thus, the technique for de- Woax•, C.B. 1976. Body-bobbingwoodcocks. Auk tection of food may have developed into an innate 93: 374-375. movement that persistsunder stressconditions. Received9 September1981, accepted11 February1982. Finally, I suggestthat this woodcockbehavior be