SEED-SIZE SELECTION IN MOURNING DOVES AND EURASIAN COLLARED-DOVES

2006·4.7 MB·English

by  Steven E Hayslette

The Wilson Journal ofOrnithology 118(1):64—69, 2006
SEED-SIZE SELECTION IN MOURNING DOVES AND
EURASIAN COLLARED-DOVES
STEVEN HAYSLETTE
E. 1
—
ABSTRACT. I studied seed-size selection among Mourning Doves (Zenaida macroura) and Eurasian Col-
lared-Doves (Streptopelia decaocto), two newly sympatric species for which mechanisms of seed selection are
not well understood. I measured and compared mean length, breadth, and thickness of seeds available to, and
consumed by, these species in feeding trials ofpenned birds. Both species selected com (Zea mays) seeds that
were shorterandnarrowerthan average, butEurasianCollared-Dovesselectedcomthatwasthickerthanaverage
and sunflower(Helianthusannuus) seedsthatwerebroaderandthickerthanaverage. MourningDovesconsumed
com of average thickness, and wheat (Triticum aestivum) and sunflower seeds of average size with respect to
all dimensions. Corn consumption by both species seems limited by seed length and breadth, but Mourning
Dove consumption of smaller seed types (wheat and milo [Sorghum vulgare]) appears largely unaffected by
seed size. Among larger seed types (com and sunflower), Eurasian Collared-Doves may select thicker- and/or
broader-than-average seeds to maximize foraging efficiency. Sunflower and com seeds consumed did not vary
between species with respect to any dimension, but Eurasian Collared-Doves seemed willing to select, and able
to eat, broader and thicker seeds than Mourning Doves, which may limit foraging competition between these
species. Received 7 February 2005, accepted 23 November 2005.
Seed selection by granivorous birds is a a species (Greig-Smith and Crocker 1986, van
complex phenomenon potentially affected by der Meij and Bout 2000), and/or correspon-
a number of factors (Ramos 1996), the rela- dence between size selection and bill size
tive contributions of which remain poorly un- among multiple species (Hespenheide 1966,
derstood in many avian granivores. In partic- Myton and Ficken 1967, Willson 1972). One
ular, seed selection by doves and other species study indicated no size preferences and/or no
that do not husk seeds before swallowing is seed size/bill size correspondence (Abbott et
not well understood; most studies of seed se- al. 1975), but this study focused on a seed-
lection in birds have focused on finches and husking species. Because doves and pigeons
other species that husk seeds during the course have relatively long slender bills and pecking
of foraging. Generally, these studies have re- behaviors that maximize speed of seed intake
vealed that the physical characteristics of without husking seeds (De Nagy Koves Hra-
seeds affecting handling time, such as size, bar and Perrin 2002), seed size may be ex-
shape, and hardness, are important determi- pected to affect seed handling and preferences
nants of preference, and that nutritional com- differently than in most species studied pre-
position of foods appears relatively unimpor-
viously.
tant (Willson 1971, Willson and Harmeson The overall goal of this project was to de-
1973, Goldstein and Baker 1984, De Nagy
termine the effect of seed size on food selec-
Koves Hrabar and Perrin 2002), especially
tion by Mourning Doves {Zenaida macroura)
without consideration of the overall econom-
and Eurasian Collared-Doves {Streptopelia
ics of nutrient intake and the factors affecting
decaocto). Eurasian Collared-Doves arerecent
it (Greig-Smith and Wilson 1985). exotic invaders of North America, and may
One approach to understanding the effectof
compete for food or other resources with na-
seed size on selection has been to examine
size selection by one or more species for a tive species, such as Mourning Doves, to the
single seed type (Hespenheide 1966, Myton detriment of native species (Romagosa 2002).
and Ficken 1967, Willson 1972, Abbott et al. Bill-size-related differences in seed-size selec-
1975, Greig-Smith and Crocker 1986, van der tion between Eurasian Collared-Doves and
Meij and Bout 2000). A number ofthese stud- Mourning Doves may mitigate competition
ies have indicated seed-size preference within between these species for food resources,
however (Poling and Hayslette 2006). Subdi-
1 Dept, of Biology, Tennessee Tech Univ., Cooke- vision offood resources among sympatric avi-
ville, TN 38505, USA; e-mail: [email protected] an granivores often is based on bill-size-relat-
64
Hayslette • SEED-SIZE SELECTION IN DOVES 65
ed differences in seed-size selection (Grant ing Doves, and would select larger corn and
1986, Faaborg 1988, Ricklefs 2001). Mourn- sunflower seeds than Mourning Doves.
ing Dove bimllmlength averages 12.83-14.53 ± METHODS
0.97-1.01 (Mirarchi and Baskett 1994),
whereas collared-dove bill length averages The first phase of this research was con-
16.9 ± 0.71 mm for males and 16.6 ± 1.02 ducted at the captive Mourning Dove research
mm for females (Romagosa 2002). Corre- facility at Auburn University, Alabama, from
sponding differences in seed-size selection June to August 2000. I used 15 2nd-year
patterns between these species may have im- Mourning Doves, captured as immatures on
portant implications regarding dietary overlap the university campus during the previous
and competition, and ultimately, coexistence breeding season; doves were initially housed
of the two species. and cared for according to Mirarchi (1993).
In cafeteria trials, previous work has indi- Priorto feeding trials, doves were fed an equal
cated that Mourning Doves and other dove mixture (by volume) ofthe four foods used in
species prefer small, round seeds such as feeding trials (described below) plus proso
wHahyistleettperoasnod Mmiirlalrecthi(P2a00n1i,cuDme NmaiglyiaKcoevuems; cmiulllaettuma).ndI brraonwdnotmolpy maislsliegtne(dPadnoivceusmtfoasfciiv-e
Hrabar and Perrin 2002), and consume rela- flocks of three birds each, and each flock was
tively few large-seeded species such as com used in a 20-hr feeding trial in a 3.7 X 7.3 X
{Zea mays and sunflower Helianthus an- 2.0-m outdoor aviary. During each trial, doves
nuus’, LeBla)nc and Otis 1998(, Hayslette and were—offered 200 seeds of each of four spe-
cies corn, black-oil sunflower, milo Sor-
Mirarchi 2001). These results appear enig- (
matic, as wild Mourning Doves are known to ghum vulgare), and wheat (Triticum aesti-
exploit com and sunflower as important food vum). Trials were preceded by >24-hr accli-
sources (Lewis 1993). De Nagy Koves Hrabar mation periods, during which doves were fed
and Perrin (2002) concluded that among Di- an equal mixture (by volume) of test seeds
baemcoonmdesDoavelsimi(tGienogpeflacitaorcuanbeoavtea)a, steheredshsoilzde toonley,acfholtrlioalw,edI ebsyti2m4a-therdfsaiszteinogfpseereidosdso.ffPerrieodr
using a sample of 20 seeds drawn at random
isimzpeo,rbtuatncbeelionwfothoadt htahrnedslhionlgd,ansidzeseilsecotfiolnit.tleI fsurroemtehaatchsi2z0es0-osfeesdeebdastcihn. sIamatptleemsptweedretoreipn--
hypothesized that seed size has little influence resentative of those in feeding batches by
on Mourning Dove selection of small seeds,
comparing the mass of each sample to the
blaurtgetrhasteepdrse,fesruecnchesasfocr,omanadncdonsusnufmlpotwiero,n aorfe, mBeacsasusoef tIhseambaptlcehdf1r0o%m owfhiecachhitbawtacsh (d2r0awonu.t
limited by seed size. Based on this hypothesis, of200 seeds), mass ofa representative sample
I predicted that Mourning Doves would pref- would be 10% of the mass of the batch from
erentially select smaller than average corn which it was drawn. Thus, a sample was
seeds, and that this within-seed-type selectiv- deemed representative and used if the ratio of
ity for size would decrease with progressively sample mass to batch mass was 0.100 ±
smaller seed types. I also hypothesized that 0.003. If not, the sample was returned to the
Eurasian Collared-Doves are less limited than batch and redrawn. Using digital calipers, I
Mourning Doves by size ofcom and sunflow- measured length, breadth, and thickness (cor-
er seeds because their bills are larger; thus, responding to the longest, intermediate-most,
they are able to exploit com and sunflower and shortest dimensions, respectively; Greig-
food sources to a greater extent than Mourn- Smith and Crocker 1986) ofeach seed in each
ing Doves. Previous research has shown that sample to the nearest 0.1 mm. Seeds of each
Eurasian Collared-Doves consume more com species were then hand-scattered on a separate
than Mourning Doves in cafeteria trials (Pol- wooden seed tray (41 X 41 X 4 cm) filled
ing and Hayslette 2006). Based on this, I pre- with commercially available topsoil; trays
dicted that Eurasian Collared-Doves would were randomly arranged in a 2 X 2 arrange-
show less within-seed-type selectivity for ment on the floor of the aviary, with 1.8 m
smaller com and sunflower seeds than Mourn- between adjoining trays. After allowing doves
66 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006
to forage from the trays for 20 hr, I removed ceded by 24-hr acclimation and fasting peri-
the trays and removed and counted the seeds ods. Seeds were scattered in trays without top-
that remained on the trays. If >20 seeds re- soil. Pre- and post-trial seed sampling and
mained, I estimated size ofseeds remaining in measurements were conducted as in the pre-
the batch using a sample of20 seeds as before vious trials, and similar analyses were con-
the trial. Analogous to pre-trial sampling, ducted separately for each species, with indi-
post-trial samples were deemed acceptable viduals serving as replicates. Additionally, I
based on comparisons of sample mass and used two-sample f-tests to compare the aver-
batch mass. A sample was used if the ratio of age length, breadth, and thickness ofseeds, by
sample mass to batch mass was within 0.003 seed type, that each dove species consumed.
of the ratio of sample seed number (20) to Trials in which doves consumed <25 seeds
batch seed number. If not, the sample was re- were omitted from analyses because I sus-
turned to the batch and redrawn. I compared pected that dove foraging during these trials
number of seeds consumed among seed types was too limited to allow for sufficientdiscrim-
using one-way analysis ofvariance (ANOVA) ination among available seeds. I did not con-
and Tukey’s procedure. I calculated mean size duct statistical comparisons of corn and sun-
ofeach pre- and post-trial sample with respect flower consumption because trial length dif-
to all three size dimensions. I calculated the fered between seed types. I conducted all
average size of seeds consumed with respect analyses using SAS/STAT (SAS Institute, Inc.
to each dimension for each seed type in each 1990) and set a = 0.05. All means are pre-
trial based on number of seeds consumed and sented ± SE.
pre- versus post-trial differences in average
RESULTS
available seed size. The formula for this cal-
culation is In the first phase (2000 Alabama study),
Se = {(200 X Sh) - [(200 - Ne) X Sa]}/Ne, caomnosnugmpsteieodntyopfesse(eFds d=ur1i1n.g9, tPria<ls 0v.a0r01i)e.d
319
where S = average size of seeds eaten, S = Doves consumed more milo, wheat, and sun-
e b
average size of seeds prior to foraging (initial flower (161.2 ± 24.3, 142.2 ± 20.4, and 103
sample), S = average size of seeds not con- ± 23.4 seeds, respectively), than corn (8.4 ±
sumed, anda Ne = number—of seeds consumed. 3.0 seeds). Doves ate nearly all (198+) ofthe
I then—used a paired Mest with trials as rep- 200 milo seeds offered in three of five trials,
licates to compare mean size consumed with and consumed almost no (<2) corn seeds in
mean size available for each size dimension two of five trials, so these seed types were
and each seed type. excluded from further analyses. One trial, in
The second phase ofthis research was con- which doves ate 198 wheat seeds, was omitted
ducted at the captive avian research facility at from analysis of wheat size consumption.
Tennessee Tech University during January- Wheat and sunflower seeds consumed were
April 2004. I used 14 Mourning Doves and average in size with respect to all dimensions
13 Eurasian Collared-Doves captured during (Table 1).
July—September 2003 in Coffee County, Ten- In the second phase (2004 Tennessee
nessee. Methods generally followed those study). Mourning Doves consumed 24.9 ±4.1
used previously, except as noted below. Indi- corn and 50.1 ± 10.3 sunflower seeds, and
viduals of each species were tested in a se- Eurasian Collared-Doves consumed an aver-
quential manner in 2.4 X 1.8 X 1.8-m pens. age of 47.0 ± 4.9 corn and 52.5 ± 8.7 sun-
Corn and sunflower seeds (n = 200) were pre- flower seeds during trials. Two collared-doves
sented to each individual in separate 5.5- and and eight Mourning Doves ate <25 corn
4-hr trials, respectively; trials involving corn seeds, and one collared-dove and four Mourn-
were longer due to the slower consumption of ing Doves ate <25 sunflower seeds; these
corn by both species. Trial order (i.e., seed doves were not included in seed-size analyses.
type) was determined randomly foreach dove, Both Mourning Doves and Eurasian Collared-
so that approximately half the individuals re- Doves selected smaller-than-average corn
ceived corn first, and half received sunflower seeds with respect to length and breadth (Ta-
first. The two trials for each dove were inter- ble 1). Mourning Doves consumed corn seeds
1
Hayslette • SEED-SIZE SELECTION IN DOVES 67
TABLE 1. Measurements (mm) ofseeds initially available to, and consumed by. Mourning Doves (MODO;
2000 and 2004) and Eurasian Collared-Doves (EUCD; 2004) in seed-size selection trials on captive birds in
Tennessee and Alabama.
Initiallyavailable Consumed
Year Food Dimension Species /ta Mean SE Mean SE
2000 Wheat Length MODO 4 6.3 0.1 6.4 0.2 -0.9
MODO
Breadth 4 3.1 0.0 3.1 0.0 0.3
MODO
Thickness 4 2.6 0.0 2.5 0.0 1.3
MODO
Sunflower Length 5 9.8 0.1 10.3 0.5 -1.1
MODO
Breadth 5 5.2 0.1 5.0 0.2 2.6
MODO
Thickness 5 3.1 0.1 2.7 0.3 2.0
MODO
2004 Corn Length 6 12.7 0.1 12.3 0.1 4.3C
EUCD 11 12.7 0.1 12.1 0.3 2.7C
MODO
Breadth 6 8.4 0.1 7.9 0.2 6.lc
EUCD
11 8.4 0.0 7.6 0.2 5.3C
Thickness MODO 6 4.5 0.1 4.6 0.3 -0.3
Sunflower Length MEUOCDDO 110 140..64 00..11 105..52 00..32 --30..40C
EUCD 12 10.2 0.1 10.2 0.4 0.2
MODO
Breadth 10 4.9 0.0 5.0 0.3 -0.1
EUCD 12 4.9 0.1 5.8 0.3 —3.0C
Thickness MODO 10 2.9 0.0 3.0 0.3 -0.3
EUCD 12 2.8 0.0 3.5 0.2 —3.5C
aSamplesize(n)equalsnumberofthree-birdflocksin2000,individualdovesin2004.
br-valuesfrompairedr-testscomparingsizesofseedsinitiallyavailableandseedsconsumed;df=n - 1.
cP<0.05.
of average thickness, but collared-doves se- in determining ease with which seeds are
lected corn seeds that were thicker than av- swallowed. Thickness seems important, how-
erage. Mean size of corn seeds consumed by ever, in species that husk seeds before swal-
the two species did not differ with respect to lowing. In a similar study of Eurasian Bull-
length, breadth, or thickness (—1.0 < tl5 < finches (Pyrrhula pyrrhula), sunflower seeds
2.8, all P > 0.11). Mourning Doves consumed consumed were 4.6% thinner, 3.1% narrower,
sunflower seeds that were ofaverage size with and 2.1% shorter than average (Greig-Smith
respect to all dimensions, and average length. and Crocker 1986). Willson (1972) concluded
breadth, and thickness ofsunflower seeds con- that Purple Finches (Carpodacus purpureus)
sumed were similar (within 0.3 mm) to aver- selected seeds based on thickness rather than
age sizes consumed by Mourning Doves in length. The sunflower seeds we used seemed
the 2000 study. Eurasian Collared-Doves con- to be below the size threshold suggested by
sumed sunflower seeds of average length, but De Nagy Koves Hrabar and Perrin (2002),
selected seeds of larger than average breadth above which size becomes a factor affecting
and thickness. Mean size of sunflower seeds dove seed handling and selection. We used
consumed did not differ (—0.7 < t20 ^ 1.6, all seeds of black oil sunflower, a relatively
P ^ 0.12) between dove species with respect small-seeded sunflower variety commonly
to any dimension. used in food plantings for Mourning Doves in
the southeastern U.S. These seeds were small-
DISCUSSION
er than sunflower seeds used in previous stud-
Results suggest that seed length andbreadth ies (Hespenheide 1966, Willson 1972, Greig-
limit Mourning Dove consumption of corn; Smith and Crocker 1986, Diaz 1990). As pre-
seed thickness seems less important in selec- dicted, consumption of smaller seeds, such as
tion. If seeds such as corn are oriented length- milo and wheat, seemed unaffected by seed
wise as they are swallowed, it seems logical size. Preference by Mourning Doves for milo
that the smaller of the two cross-sectional di- in this study agrees with preference patterns
mensions (thickness) would be less important documented elsewhere (Poling and Hayslette
68 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 1, March 2006
2006), and suggests that seed preference in Previous authors have expressed concern
this species may be based, at least in part, on about how the recent Eurasian Collared-Dove
seed size and/or shape. Selection patterns fa- invasion of North America may affect native
voring small seeds have been documented in species, particularly ecologically similar spe-
several studies of seed-husking species (Hes- cies, such as the Mourning Dove, with which
penheide 1966; Willson 1971, 1972; Keating Eurasian Collared-Doves may compete (Rom-
et al. 1992), but De Nagy Koves Hrabar and agosa and McEneaney 1999, Romagosa and
Perrin (2002) suggested that dove food pref- Labisky 2000, Romagosa 2002). A recent
erences are influenced more by seed shape study of food-selection patterns of these two
than size; round seeds are handled more rap- dove species revealed a high degree (95%) of
idly than, and preferred to, elongate seeds. Be- dietary overlap between them (Poling and
cause milo was both the smallest and roundest Hayslette 2006), although this was based on
of the seeds we tested, it is impossible to tell relative consumption ofdifferent seed types in
which ofthese seed characteristics actually in- a cafeteria experiment, rather than on size
fluenced seed selection. preferences within seed types. If genuine, the
As with Mourning Doves, consumption of Eurasian Collared-Dove’s preferences for
corn by Eurasian Collared-Doves seems lim- seeds that are broader and/or thicker than
ited by seed length and breadth. In contrast to those selected by Mourning Doves may result
Mourning Doves, however, Eurasian Collared- in differential exploitation of larger seeds,
Doves were influencedby corn seedthickness, such as corn and sunflower, and concomitant
choosing thicker-than-average seeds. If seed mitigation of foraging competition between
thickness is relatively unimportant in deter- them. Partitioning of food resources among
mining handling and/or swallowing efficiency, sympatric species based on seed size has been
as postulated earlier for Mourning Doves, per- documented in a number of avian granivore
haps the Eurasian Collared-Dove’s selection communities (Grant 1986, Faaborg 1988,
of thicker seeds increases foraging efficiency Ricklefs 2001). Similarly, limited foraging
by increasing nutrient intake (benefit) per unit competition may mean greater potential for
handling time (cost) (Stephens and Krebs coexistence of Mourning Doves and Eurasian
1986). Likewise, selection of broader- and Collared-Doves than previously believed.
thicker-than-average sunflower seeds may in-
ACKNOWLEDGMENTS
crease foraging profitability of Eurasian Col-
lared-Doves. Selection for large foods, pre-
sumably to maximize foraging profitability, SmiItth,hanDk. MSm.itPh.,CoCo.k,SpiAll.erG,oJo.dTmuarnne,r,T.anDd. TP.olMin.g,UnC-.
has been reported in other seed-eating birds deutsch for assistance with data collection. Funding
(Myton and Ficken 1967, Ramos 1996). and other support for this project was provided by the
Selection of larger than average corn and Alabama Department ofConservation and Natural Re-
sunflower seeds with respect to certain dimen- sources (Division of Wildlife and Freshwater Fisher-
sions by Eurasian Collared-Doves, but not by ies), Auburn University School ofForestry and Wild-
life Sciences, Tennessee Tech University Department
Mourning Doves (paired Mests), suggests that ofBiology, andTennesseeWildlife ResourcesAgency.
collared-doves select thicker corn seeds, and This research was approved by, and conducted in ac-
broader and thicker sunflower seeds, than do cordance with, the Auburn University InstitutionalAn-
Mourning Doves. Although direct between- imal Care and Use Committee (protocol review num-
species comparisons of average seed sizes ber 0009-R-0786), and Tennessee Tech University In-
consumed failed to reveal any such differenc- stitutional CommitteefortheCare andUseofLabAn-
imals in Experimentation (protocol review number
elsa,retdh-edoavveesrawgaesc0o.r5nmsmeedthiccoknersutmheandtbhayt ceoalt-- r1e[f0e2r-e0e3s])f.orItthehiarnkcoMm.meRn.tsPerorninananedarltiweor darnaoftnyomfotuhse
en by Mourning Doves, and the average sun- manuscript.
flower seed consumed by collared-doves was
0.8 mm broader and 0.5 mm thicker. Selection LITERATURE CITED
for larger seeds by Eurasian Collared-Doves
than by Mourning Doves likely is related to AbboStete,dIs.,elLe.ctiKo.n aAnbdbohtatn,dlianngdabPi.liRt.yoGfrfaonutr.sp1e9c7i5e.s
differences in their bill sizes (Hespenheide ofDarwin’s Finches. Condor 77:332-335.
1966, Myton and Ficken 1967, Willson 1972). De Nagy Koves Hrabar, H. and M. Perrin. 2002.
- .
Hayslette • SEED-SIZE SELECTION IN DOVES 69
The effect of bill structure on seed selection by M. W. Sayre, R. E. Tomlinson, and R. E. Mirarchi,
granivorous birds. African Zoology 37:67-80. Eds.). Stackpole Books, Harrisburg, Pennsylvania.
Diaz, M. 1990. Interspecific patterns ofseed selection Mirarchi, R. E. and T. S. Baskett. 1994. Mourning
among granivorous passerines: effects ofseed nu- Dove (Zenaida macroura). The Birds of North
tritive value and bird morphology. Ibis 132:467- America, no. 117.
476. Myton, B. A. and R. W. Ficken. 1967. Seed-sizepref-
Faaborg, J. 1988. Ornithology: an ecological ap- erence inchickadeesandtitmice in relationtoam-
proach. Prentice-Hall, EnglewoodCliffs,NewJer- bient temperature. Wilson Bulletin 79:319—321
sey. Poling, T. D. and S. E. Hayslette. 2006. Dietary
Goldstein, G. B. and M. C. Baker. 1984. Seed se- overlapandforagingcompetitionbetweenMourn-
lection byjuncos. Wilson Bulletin 96:458-463. ing Doves and Eurasian Collared-Doves. Journal
Grant, P. R. 1986. Ecology and evolution ofDarwin’s ofWildlife Management 70: In press.
finches. Princeton University Press, Princeton, Ramos, J. A. 1996. The influence of size, shape, and
New Jersey. phenolic content on the selection of winter foods
Greig-Smith, P. W. and D. R. Crocker. 1986. Mech- by the Azores Bullfinch (Pyrrhula murina). Jour-
arhnuilsamspyorfrfhouoldasLi.z)e sfeeleedcitniognobny Bsuulnlfflionwcehress(ePeydsr. Ricklneaflso,fRZ.oEo.lo2g0y012.3T8:h4e15e-c4o3n3o.my ofnature, 5th ed.
Animal Behaviour 34:843-859. W. H. Freeman and Company, New York.
Greigo-fSmsieetdh,sPi.zeW,.nautnrdieMnt. cF.omWpiolssiotni.on19a8n5.dIpnhfelnuoelnicce Roma(gStorseap,topCe.liaM.de2c0a0o2c.toE).uraTshieanBiCrodlslaorfed-NDorotvhe
America, no. 629.
content on the preferences of bullfinches feeding
in ash trees. Oikos 44:47-54. Romagosa, C. M. and R. F. Labisky. 2000. Establish-
Hayslette, S. E. and R. E. Mirarchi. 2001. Patterns ment and dispersal ofthe EurasianCollared-Dove
of food preferences in Mourning Doves. Journal in Florida. Journal of Field Ornithology 71:159-
165.
ofWildlife Management 65:816-827.
Hespenheide, H. A. 1966. The selection of seed size RomaCgoolslaa,reCd.-DMo.veanindNT.orMtchEnAemaenriecya. a1n9d99.thEeurCaasriiabn-
by finches. Wilson Bulletin 78:191-197. bean. North American Birds 53:348-353.
Keating,J. E, R. J. Robel, A. W. Adams, K. C. Behn- SAS Institute, Inc. 1990. SAS/STAT guide for per-
ke, and K. E. Kemp. 1992. Role ofhandling time sonal computers, ver. 6. SAS Institute, Inc., Cary,
in selection ofextruded food morsels by two gra- North Carolina.
nivorous bird species. Auk 109:863-868. Stephens, D. W. andJ. R. Krebs. 1986. Foraging the-
LeBlanc, D. K. and D. L. Otis. 1998. Preferencesby ory. Princeton University Press, Princeton, New
Mourning Doves and two granivorous songbirds
Jersey.
for selected seeds. Proceedings of the Annual van der Meij, M. A. A. and R. G. Bout. 2000. Seed
Conference of the Southeastern Association of selection in the Java Sparrow (Padda oryzivora):
Fish and Wildlife Agencies 52:324-335. preference and mechanical constraint. Canadian
Lewis, J. C. 1993. Foods and feeding ecology. Pages Journal ofZoology 78:1668-1673.
181-204 in Ecology and management of the Willson, M. F. 1971. Seed selection in some North
Mourning Dove (T. S. Baskett, M. W. Sayre, R. American finches. Condor 73:415-429.
E. Tomlinson, and R. E. Mirarchi, Eds.). Stack- Willson, M. F. 1972. Seed size preference in finches.
pole Books, Harrisburg, Pennsylvania. Wilson Bulletin 84:449-455.
Mirarchi, R. E. 1993. Careand propagationofcaptive Willson, M. F. andJ. C. Harmeson. 1973. Seed pref-
Mourning Doves. Pages 409-428 in Ecology and erences and digestive efficiency ofCardinals and
managementoftheMourning Dove(T. S. Baskett, Song Sparrows. Condor 75:225-234.