SHORT COMMUNICATIONS 231

well-corroborated phylogeny for the Thamnophilinae. HILTY, S. L., AND W. L. BROWN. 1986. A guide to Nevertheless,Xenornis Setifronsand the allopatric, sib- the birds of Colombia. Princeton Univ. Press, ling speciespair of Thamnomanescaesius and T. schis- Princeton, NJ. togynusappear to be ecologicalcounterparts, sharing REMSEN,J. V., JR., AND S. K. ROBINSON. 1990. A a niche rare within the Thamnophilinae. classificationscheme for foragingbehavior of birds in terrestrial habitats. Studies in Avian Biology We thank Thomas Schulenbergfor his helpful com- No. 13:144-160. ments on the manuscript. RIDGELY,R. S., AND J. A. G~YNNE. 1989. A guide LITERATURE CITED to the birds of Panama. Princeton Univ. Press, Princeton, NJ. CHAPMAN,F. M. 1917. The distribution of bird-life SCHULENBERG,T. S. 1983. Foraging behavior, eco- in Colombia. Bull. Am. Mus. Nat. Hist. 36: 106. morphology and systematicsof some antshrikes CHAPMAN,F. M. 1924. Descriptions of new genera (Formicariidae: Thamnomanes).Wilson Bull. 95: and speciesof Tracheophonaefrom Panama, Ec- 505-521. uador, Peru, and Bolivia. Am. Mus. Novit. 123: WETMORE,A. 1972. Birds of the Republic of Panama. l-9. Part 3. Passeriformes:Dendrocolaptidae (Wood- HAF~ER,J. 1975. Avifauna of northwestern Colom- creepers)to Oxyruncidae (Sharpbills). Smithson- bia, South America. Bonner Zool. Monog., no. 7, ian Institution Press, Washington, DC. Bonn.

The Condor 95:231-233 0 The CooperOrnithological Society 1993

PREY TRANSPORT BY LOGGERHEAD SHRIKES ’

REUVENYOSEF Department of Zoology, The Ohio State University,1735 Neil Ave., Columbus,OH 43210, and ArchboldBiological Station, P.O. Box 2057, Lake Placid, FL 33852

Key words: Foraging;Loggerhead Shrike; Lanius lu- port over the same distance.Carlson (1985) found that dovicianus;prey transport:Florida. Red-backed Shrikes (Lanius collurio) delivered to fe- males prey collectedclose to the nest; he reasonedthat Recent studies demonstrate that avian single-prey the range of prey sizes economically worth returning loaders preferably transport larger prey to their nests decreasedwith distance and, inversely, the range of (e.g., Gronlund et al. 1970, Carlson 1985, Krebs and prey sizesavailable for self-feedingincreased with dis- Avery 1985, Sonerud 1989). For central-foragingpred- tance. ators that carry prey for further handling and caching Studies of hunting by Loggerhead Shrikes (Lanius or for feeding of mates or young, the value of the prey ludovicianus)are limited to foragingbehavior (e.g., Bo- is influenced by the energeticcost of transport (Orians hall-Wood 1987). nrev selection(ea.. Kaufman 1973). and Pearson 1985). and reproductive requirements and ‘capabilities (e.g:: Shrikes (Laniinae) are birds of open-savannahhab- Kridelbaugh 1982, Novak 1989), and opportunistic itats that exhibit central-place foraging and caching observationswherein large prey are reported (e.g., Bal- behavior. Northern Shrikes (Lanius excubitor)trans- da 1965). Shrikes are reported carrying prey of ap- port whole arthropods and reptiles to the nest, but proximately their own body mass in their feet (e.g., decapitate mammalian prey (Gronlund et al. 1970). Conlev 1982, Inaold and Inaold 1978). and carrvina This speciesusually transports a higher-than-optimal smaller prey in their beaks (e.g., Chapman and C&to load size, compared to other avian predators such as 1972). However, mode of prey transport and distance the EurasianKestrel (F&o tinnunculus)(Sonerud 1989). flown with prey as functions of prey body mass are Sonerud (1989) reasoned that the optimal load-size unstudied. carried by a Northern Shrike made up a higher percent The LoggerheadShrike (mean body mass on study of the body mass than it did for a Kestrel, becausethe site 47.9 * 3.3 SD. n = 103) is an exclusivecarnivore. relative cost of flying increaseswith increasing body Becauseprey carried in the bill should destabilize a mass. Sonerud also found that central-place foraging flying bird and consequentlyincrease energetic costs, birds which differed in size and exploited the same I postulated that to maintain a more stable center of prey type, differed in their selection of prey for trans- gravity, prey items weighingmore than some threshold value would be carried in the feet rather than in the bill. I studied post-breeding LoggerheadShrikes during ’ ’ Received 16 July 1992. Accepted 26 October 1992. October-December 1991 at the 4.300 ha MacArthur 232 SHORT COMMUNICATIONS

50 -

40 -

30 -

20 -

IO-

” ---- BeakOnly ’ Beak to Feet Feet Only

Mode of Transport

FIGURE 1. Mode of transport of 78 house mice by 23 LoggerheadShrikes. The boxes indicate averagebody mass of mice, and error bars indicate the standard deviation.

Agro-ecology Research Center of the Archbold Bio- 2 df, P = 0.7738). Using the Fisher Planned Least logical Station, Lake Placid, Florida. I captured terri- SignificantDifference Test, significantdifferences were torial shrikes in composite treadle/bal-chatri traps found at the 95% level between the modes of transport (Yosef and Lohrer 1992) and banded them for indi- (beak only vs. beak and feet = 4.1; beak only vs. feet vidual recognition with the United States Fish and only = 3.4, beak and feet vs. feet only = 3.7). Average Wildlife Servicealuminum bandsand color bands,and body mass of prey transported in the beak only was usedthe shrikes’ aggressiveresponses to playbacksand 18.3 f 7.5 g (range 9.0-30.5 g, n = 22) and flew an taxidermic mounts to map the borders of all territories averageof 65 m. Shrikesmoved prey from beak to feet on the ranch. in 18 instancesand average mass of prey was 27.3 f I offered 23 individual shrikeslaboratory mice (Mus 3.1 g (range 23.9-36.8 g, n = 18), and flew an average musculus)ranging in size from 9.0 to 6 1.9 g. All mice of 49 m. Body mass of prey transported only in the (n = 78) were weighed on a Acculab electronic digital feet averaged39.6 f 6.9 g (range 29.2-6 1.9 g, n = 38) scale (+O. 1 g). Distances were measured with optical and flew an average of 35 m. range finders (Ranging Inc., models 120 and 620, ac- Results conform with the modes of transport pre- curacy ?2%). For the birds’ initial flight with the prey, viously reported for free-ranging LoggerheadShrikes. I recorded the mode of transport (beak, feet, beak to Prey body mass was significantly related to distance feet while in flight) and distance flown. carried. Prey carried in feet ranged from 50 to 129% The average initial distance flown with prey in the of the shrike’s averagebody mass. This range includes beak only was 6.4 m, in beak and feet 4.8 m, and in values for species previously observed transported. feet only was 4.5 m (Table 1). Body mass of prey sig- Shrikes have been observed in unsuccessfulattempts nificantly affectedmode of transport (Factorial analysis to lift heavy prey with their bills (Balda 1965, Comer of variance, F = 17.78, 2 df, P = 0.000 1, Fig. l), and and Freeland 1980). Hopkins (1953) Caldwell (1967) distance flown with prey after being disturbed (Fac- and this studycontradict Bent ’s (1950) view that shrikes torial ANOVA, F = 5.92, 2 df, P = 0.05 l), however, do not usetheir feet to transport prey, but depend upon it did not affect the overall initial distance Aown after the bill to seize and carry prey. Slack (1975) expected retrieving the mouse (Factorial ANOVA, F = 0.512, that selection by shrikes would be affected by size of

TABLE 1. The averagedistance (m) flown by LoggerheadShrikes using three different modes of transport. (1) denotes beak only, (2) beak and feet, and (3) feet only.

Avg. body mass Initial distance Disturbed distance (9) T? SD Range -t_ SD Range n 1 18.3 6.4 f 4.2 1-21 64.6 i 22.2 30-97 22 2 27.3 4.8 f 2.7 l-9 49.1 + 28.1 lo-58 18 3 39.6 4.5 + 2.2 l-9 35.1 + 23.3 8-65 38 SHORT COMMUNICATIONS 233 the prey. The current analysis indicates that Logger- CALDWELL,L. D. 1967. Attack behavior of a Log- head Shrikes will readily attack and carry prey up to gerheadShrike. Wilson Bull. 79: 116-l 17. at least 129% their own body mass; it is possible that CA&ON, A. 1985. Central place foragingin the Red- they can carry heavier prey. backed Shrike: allocation of prey between forager Moving of prey from the beak to the feet while in and sedentary consumer. Anim. Behav. 33:664- flight was previously reported by Esterly (19 17). The 666. &rent study shows that prey of intermediate mass CHAPMAN,B. R., ANDS. D. CASTO. 1972. Additional (50-92% of shrike bodv mass) are readilv carried in vertebrate prey of the LoggerheadShrike. Wilson ihe beak during take-o& but apparently are more ef- Bull. 84:496-497. ficiently transported if moved to the feet. This weight COMER,C. W., AND J. B. FREELAND. 1980. Logger- range overlaps that in which shrikescarried their prey head Shrike observedkilling Cardinal. Bull. &la- in the beak (19-58% of shrike mass) or feet (61-131% homa Omithol. Sot. 13:13-l 5. of shrike mass). Between the prey mass of 52-60% of CONLEY,M. R. 1982. Apparent predation on Homed shrike mass, however, prey transport usually involved Lark by LoggerheadShrike. SouthwestNatur. 27: transfer from beak to feet (10 of 11 trials). 367. The high variation in the results of this study may ESTERLY,C. 0. 1917. How does the shrike carry its have been partially influenced by environmental fac- prey? Condor 19~25. tors (e.g., wind speedsand direction in relation to the GRONLUND,S., J. ITAMIES,AND H. MIKKOLA. 1970. bird) that were not recorded, and so could not be treat- On the food and feeding habits of the Great Grey ed as covariates in the model. It remains to be deter- Shrike in Finland. Omis. Fenn. 47: 167-l 7 1. mined whether shrikesin varying environmental con- HOPKINS,M. 1953. Feeding methods of the shrike. ditions will change the range of body mass of prey Oriole 18:19. transported as a function of the mode. INGOLD,J. J., AND D. A. INGOLD. 1987. Loggerhead It is probable that carrying prey in the feet stabilizes Shrike kills and transports a Northern Cardinal. the shrike while in flight and that beyond some thresh- J. Field. Omithol. 58:66-68 old mass, prey held in the beak destabilizesthe shrike KAUFMAN,D. W. 1973. Shrike prey selection:color and increases the energetic cost of transport. Thus, or conspicuousness?Auk 90:204-206. small prey are transported in the beak, intermediate KREBS, J. R., AND M. I. AVERY. 1985. Central place prey in beak and then feet, and heavy prey only in the foragingin the EuropeanBee-eater. J. Anim. Ecol. feet. 541459-472. KRIDELBAUGH,A. L. 1982. An ecological study of F. E. Lohrer, T. C. Grubb, Jr., P. Midford, Steve Loggerhead Shrikes in central Missouri. Sherrod and an anonymousreviewer provided helpful M.Sc.thesis, Univ. of Missouri, Columbia, MO. comments on an earlier draft of this manuscript. This NOVAK, P. G. 1989. Breeding ecology and status of study was done while the author was supportedby the the LoggerheadShrike in New York state. M.Sc. Frank M. Chapman Memorial Fund of the American thesis. Cornell Univ.. Ithaca. NY. Museum of Natural History, Cruickshank Research ORIANS,G. H., AND N. l? PEARSON. 1985. On the Award of the Florida Ornithological Society, and the theory of central place foraging,p. 155-I 77. In D. Grants-in-Aid of Research of the Sigma Xi Society. J. Horn. B. R. Stairs. and R. D. Mitchell leds.1. This is contribution 11 of MAERC of Archbold Bio- Analysis of ecologicalsystems. Ohio State I&iv:; logical Station. Columbus. OH. SLACK,R. S. 1975. Effectsof prey size on Loggerhead LITERATURE CITED Shrike predation. Auk 92:8 12-8 14. BALDA,R. P. 1965. LoggerheadShrike kills Mourning SONERUD,G. A. 1989. Allocation of prey between Dove. Condor 67:359. self-consumption and transport in two different- BENT,A. C. 1950. Life histories of North American sized central place foragers. Omis Stand. 20:69- wagtails,shrikes, vireos, and their allies. U.S. Natl. 71. Mus. Bull. 197. YOSEF, R., AND F. E. LOHRER. 1992. A composite BOHALL-WOOD,P. 1987. Abundance,habitat useand treadlejbal-chatri trap for Loggerhead Shrikes. perch use of Loggerhead Shrikes in northcentral Wildl. Sot. Bull. 20: 116-l 18. Florida. Wilson Bull. 99:82-86.