Author Institution: The Institute of Environmental Sciences and Department of Zoology, Miami Universit

Barrett, Gary W.

Kruse, Elizabeth A.

Trumpy, R. David

The Ohio Journal of Science

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Copyright © 1983 Ohio Acad. Sci. O030-0950/83/OOO1-OO65 $1.00/0BRIEF NOTEPREY COAT COLOR SELECTION AND BIOENERGETICSOF CAPTIVE SCREECH OWLS1R. DAVID TRUMPY, GARY W. BARRETT and ELIZABETH A. KRUSE, The Institute of Environ-mental Sciences and Department of Zoology, Miami University, Oxford, OH 45056.OHIOJ. SCI. 83 (1): 65-67, 1983There is disagreement concerning theprimary factor controlling screech owl-small mammal prey selection behavior.Previous studies have shown screech owls(Otus asio) select transient over residentwhite-footed mice (Peromyscus leucopus)(Metzgar 1967), white over agouti housemice {Mus musculus) (Kaufman 1974c), ac-tive over inactive house mice (Kaufman1974b), conspicuous over nonconspicuousold-field mice {Peromyscuspolionotus) (Kauf-man 1974a), and smaller over larger whitelaboratory mice (Marti and Hogue 1979).In this study, we attempted to holdconstant the above factors (e.g., habitatfamiliarity and prey size) as well as suchvariables as habitat cover (Sparrowe 1972),hunger (Mueller 1973), energy content(Emlen 1966), and energy reward (Barrettand Mackey 1975) in an attempt to evalu-ate the role of coat color (i. e., conspicuous-ness) in screech owl-small mammal preyselection and bioenergetic relationships.This study was conducted at theMiami University Ecology ResearchCenter near Oxford, Ohio. An aviary(9.1 X 6.1 X 3.7 m), described in detailby Barrett and Mackey (1975) and Wallickand Barrett (1976), was divided into2 identical compartments, each with a vol-ume of 102.7 m3. Wooden perches, 2.5 mhigh, were placed in the 4 corners andacross the middle of each aviary. A shelterbox (0.6 X 0.5 X 0.9 m) was attached tothe west wall of each aviary approximatelyManuscript received 10 July 1981 and in revisedform 21 August 1981 (#81-31).3.0 m above ground level. The west wallwas covered with burlap to provide shadeand to visually separate the owls. In addi-tion, tree branches were situated aroundthe nest box to provide for a more naturalroosting site.Vegetation in each aviary consisted offescue (Festuca elatior), giant foxtail (Setariafaberii) and Kentucky blue grass (Poapratensis). Vegetation was maintained at aheight of approximately 10 cm becausedeer mice {Peromyscus maniculatus), the preyspecies used in the study, prefer an area ofsparse'vegetative cover (Verts 1957).An adult screech owl (wild captured)was placed in each aviary on 30 October1977 for a 3-day acclimation period. Dur-ing this time, the owls were fed whitelaboratory mice {Mus musculus). The owlsand any remaining mice were removed fol-lowing the acclimation period. The screechowls were weighed at the beginning(4 November) and the end (17 November)of the experiment. A mean weight value of168 g compared favorably with the 172 gmean weight reported by Craighead andCraighead (1969).Deer mice, a major constituent of thescreech owl's diet (Craigheacl and Craig-head 1969), were introduced into the avi-aries on 2 November 1977. Each aviarycontained 10 (5 male, 5 female) normal,wild Peromyscus and 10 (5 male, 5 female)mutant, blond Peromyscus. The mean bodyweight for both the wild and blond strainswas 15.8 g. Each mouse was toe-clippedand marked with a # 1 monel eartag. Micewere allowed a 2-day acclimation period6566 TRUMPY ET AL. Vol. 83before being subjected to owl predation.The Peromyscus diet was supplementedwith 75 g of wild bird seed handsownevenly at 2-day intervals. Owl pellets werecollected daily, oven-dried at 80 C for72 h, weighed and examined for tags ofmice consumed.A caloric equivalent of 2.50 kcal/gdry wt for Peromyscus (Kaufman et al.1975) was employed in the computation ofscreech owl ingestion rates. Feces were cal-culated using Graber's (1962) estimate of8% of the average food intake. Secondaryproduction (growth) was considered to bezero since no significant amount of in-gested energy was channeled into weightgain.Observations revealed both strains ofPeromyscus successfully adapted to theirhabitat and became quite active at dusk,i.e., at the time when the screech owlsinitiated their hunting and feeding activi-ties. Feeding was initiated at dusk whenboth the blond and wild types Peromyscuscould be easily distinguished. Basedon feeding data obtained during the in-itial 7 days of the study, 62% (13 of 21)of the mice taken were of the blond(i.e., more conspicuous) strain. Chi-square analysis, however, revealed nosignificant selection preference (df = 1,xr= 1.19, P > 0.05).Regression analysis indicated the re-moval patterns of both blond and wildPeromyscus followed linear functions. Thelinear function for the blond mutantwas Y = 90.0 - 8.04 X (r2 = 0.90;P < 0.001) while that for the wildwas Y = 9.54 - 5.65 X (r2 = 0.94;P < 0.001), where Y equals the percentremaining and X equals time in days. Nosignificant difference (P > 0.05) wasfound between the slopes of these 2 lines.A mean ingestion rate of 0.35 kcal • glive wt • day * was computed for thescreech owls feeding exclusively on the Per-omyscus populations. Mean energy lost inthe form of pellets was 0.04 kcal • g livewt 1 • day" . Since neither bird exhibiteda significant weight change, secondaryproduction was zero.Assimilation energy (ingestion—pellets—feces) was 0.28 kcal • g live wt"1 • day"1.Respiration (assimilation energy-secondary production) was also 0.28kcal • g live wt"1 • day"1. Mean assimi-lation efficiency (ingestion energy—nonassimilated energy/ inges t ionenergy X 100) was 80%.We hypothesized the screech owlswould select the light-colored (blond) mu-tant over the normal (wild-type) coat colordeer mice. This hypothesis should havebeen reinforced by reeding the owls whitelaboratory mice (i. e., by the possibility offorming a specific searching image) beforebeing introduced into each aviary. Theowls, however, did not select the moreconspicuous prey.Both adult owls used in the presentstudy had previously existed under naturalhabitat conditions and had, undoubtedly,fed on wild Peromyscus. To initiate a signifi-cant short-term shift toward conspicuousprey, selection may be related to (a) thedegree of prey coat color difference, (b) theage of the predator, (c) a complementaryhabitat factor (e.g., soil color contrast), or(d) prey selection rates associated withtemporal or spatial habitat differenceswhich are difficult to identify under semi-natural or natural field conditions. Futurestudies should focus upon prey containedwithin large experimental enclosures (e.g.,Spencer and Barrett 1980) where long-term selection rates could be determined.Ingestion and assimilation values ofthese owls, which consumed exclusivelyPeromyscus, were compared with values ofowls presented with a different small mam-mal prey diet. Postler and Barrett (1981)found that screech owls appeared to selectMicrotus as the primary food source, al-though Peromyscus were considered to beequally abundant and vulnerable — a feed-ing behavior which resulted in a largerenergy reward. The Postler and Barrett(1981) study was conducted under similarexperimental conditions. They found in-gestion and assimilation values of 0.37OhioJ. Sci. OWL PREY SELECTION AND BIOENERGETICS 67and 0.28 kcal • g live wt l • day \ re-spectively. Interestingly, these valueswere nearly identical to the 0.35 and0.28 kcal • g live wt"1 • day"1 values ob-served in the present study. Our screechowl ingestion rate is also comparable to the0.34 kcal * g live wt 1 • day l fall andwinter values reported for screech owls byCraighead and Craighead (1969). Differ-ences in food choice, therefore, appear notto cause significant changes in screech owlbioenergetics.ACKNOWLEDGMENTS. We thank Scott Davis,Mark Knight, Lynn Postler, Scott Springer andVicki Teubner for helping in the construction ofthe aviary. We also thank Drs. Donald W. Kauf-man, Carl D. Marti, Eugene P. Odum and David R.Osborne for constructive criticism of the manu-script. We are grateful to Dr. Robert Robbins,John A. King Laboratory, Michigan State Uni-versity, for the blond, mutant strain of mice andMrs. Ruth McLeod for manuscript preparation. Thisstudy was supported by a grant from the MiamiUniversity Research Committee.LITERATURE CITEDBarrett, G. W. and C. V. Mackey 1975 Prey se-lection and caloric ingestion rate of captiveAmerican Kestrels. Wilson Bull. 87: 514-519-Craighead, J . J . and F. C. Craighead 1969Hawks, owls, and wildlife. Dover Publ. Inc.,NY. p. 1-443.Emlen, J. M. 1966 The role of time and energyin food preference. Amer. Nat. 100: 611-617.Graber, R. R. 1962 Food and oxygen consump-tion in three species of owls {Strigidae). Condor64: 473-487.Kaufman, D. W. 1974a Adaptive coloration inPeromyscus polionotus: Experimental selection byowls. J. Mammal. 55: 271-283.1974b Differential predation on activeand inactive prey by owls. Auk 91: 172-173.197'4c Differential owl predation onwhite and agouti Mus musculus. Auk 91: 145-150.G. A. Kaufman and J. G. Wiener 1975Energy equivalents for sixteen species of xericrodents. J. Mammal. 56: 946-949-Marti, C. D. and J. G. Hogue 1979 Selection ofprey by size in screech owls. Auk 96: 319-327.Metzgar, L. H. 1967 An experimental com-parison of screech owl predation on resident andtransient white-footed mice (Peromyscus leucopus).J. Mammal. 48: 387-391-Mueller, H. C. 1973 The relationship of hungerto predatory behavior in hawks (Falco sparveriusand Buteoplatypterus). Anim. Behav. 21: 513-520.Postler, J. L. and G. W. Barrett 1982 Prey selec-tion and bioenergetics of captive screech owls.OhioJ. Sci. 82: 55-58.Sparrowe, R. D. 1972 Prey-catching behavior inthe sparrow hawk. J. Wild. Manag. 36: 297-308.Spencer, R. S. and G. W. Barrett 1980 Meadowvole population response to vegetational changesresulting from 2, 4-D application. Amer. Midi.Nat. 103: 32-46.Verts, B.J. 1957 The population distribution oftwo species of Peromyscus on some Illinois strip-mined land. J. Mammal. 38: 53-59-Wallick, L .G. and G. W. Barrett 1976Bioenergetics and prey selection of captive barnowls. Condor 78: 139-141.

Prey Coat Color Selection and Bioenergetics of Captive Screech Owls

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Prey Coat Color Selection and Bioenergetics of Captive Screech Owls

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