Download The Importance of Open Habitat to the Occurrence of Kleptoparasitism

July1985]
Short
Communications
erated from cells with inadequate sample sizes. No
test was conducted
on the Tule
Lake NWR
data be-
cause t-tests indicated the mean water-depth categorieswere not different. Bear River NWR and Lower Klamath
NWR
data sets revealed
no difference
in
water-depth use by Western Grebe color morphs.
I also tested for differences in the proportion of
each color morph at each water-depth zone (Miller
1981: 219). Of 15 casestested, only 3 were significantly different: medium and high zones at Lower
Klamath NWR and the low zone at Upper Klamath
Lake.
The data support the hypothesisthat light-phase
Western
Grebes feed farther
from
shore than dark-
phase birds. However, the data are not totally consistentand, thus,this questionwarrantsfurther study.
The data do not supportthe hypothesisthat lightphase Western Grebes feed at greater water depth
than dark-phasebirds. However, the data must be
viewed with cautiondue to severalconfoundingfactors:(1) water-depthcategorieswere not directly related to distancecategories;(2) 3 of 5 study areas
were artificial water impoundmentswith relatively
little change in water depth throughout the water
basin (with the exceptionof "borrow ditches"adjacent to dike roads);and (3) the depth categorieswere
only relative to other measurements
on the samelake.
Future
research
should
concentrate
on natural
water
basins to minimize these factors. Unfortunately,
however, nearly all of the sympatric breeding populations in the U.S. are on artificial impoundments.
One notable exception is Upper Klamath Lake.
A general hypothesiscan be developedfrom these
data. Most
natural
water
basins have
the shallowest
water zones adjacent to shore, and water depth increaseswith approachto the approximatecenter of
the basin. Light-phase birds may have evolved behavioral patternscloselyassociated
with water depth.
Useof a particularwater-depthzonecommonlymay
occurat a fairly consistentdistancefrom shore.Thus,
distancefrom shoremay be an environmental"cue"
regarding water depth and niche partitioning between the color morphs.Reducedniche overlap may
637
limit competition for food resources,i.e. a "coexistencemechanism"(Cody 1974:7). An alternative hypothesisis that niche partitioning is accomplishedby
spatialseparationof near shorevs. farther from shore,
and water depth and the evolution of "springing
dives" are secondaryto spatialfactors.In either case,
at artificial water impoundment areas where mean
water depth is relatively similar (comparedto natural
water impoundments), distance from shore may influence spatial behavior of birds more than water
depth.
Travel support was provided by the Wildlife Biology Program,WashingtonStateUniversity. Dr. Tom
McCabe
assisted with
field work
and reviewed
the
manuscript. Duane Diefenbach assistedwith data
analysis. Sincere thanks to Drs. Rich Alldredge and
Gary White for statisticalconsultation,and Drs. Fred
Gilbert, RichardJohnson,John Kadlec,Gary Nuechterlein, Vince Schultz, John Thompson, and Kerry
Reesefor valuable commentson the manuscript.
LITERATURE CITED
CODY,M.L. 1974. Competition and the structureof
bird communities. Monographs in Population
Biology No. 7. Princeton,New Jersey,Princeton
Univ.
Press.
GRINNELL,J. 1904. The origin and distribution of
the Chestnut-backed
MILLER, R. G.
1981.
Chickadee.
Simultaneous
Auk 21: 364-382.
statistical infer-
ence, 2rid ed. New York, Springer-Verlag.
NUECHTERLEIN,
G.L. 1981. Courtship behavior and
reproductive isolation between Western Grebe
color morphs. Auk 98: 335-349.
RATTI,J. T. 1979. Reproductive separation and isolating mechanismsbetween syrupatticdark- and
light-phase Western Grebes. Auk 96: 573-586.
1981.
Identification
Clark's Grebe. Western
and
distribution
of
Birds 12: 41-46.
STORER,
R.W. 1965. The color phasesof the Western
Grebe. Living Bird 4: 59-63.
Received18 ]une 1984,accepted19 December1984.
The Importanceof Open Habitat to the Occurrenceof Kleptoparasitism
DENNIS R. PAULSON
BurkeMuseumDB-10,University
of Washington,
Seattle,Washington
98195USA
Direct competitionamong predatory birds for potential prey often is observedbecauseof the large
sizeof predatorand prey, the often lengthy pursuit,
and the open terrain in which many of thesebirds
live. Suchcompetitionwas brought to my attention
vividly when I watchedthe interactionamongfour
speciesof raptorsover an open grassyprairie near
Clewiston,Hendry County, Florida on 26 November
1961.A Merlin (Falcocolumbarius)
flew rapidly over
the prairie about0.5 m abovethe ground and flushed
two male Red-winged Blackbirds(Agelaiusphoeniceus).It followed one blackbird closelyuntil a male
Northern Harrier (Circuscyaneus)rose from the prairie in front
of them
and struck
at but missed the
passing blackbird. The blackbird dropped to the
ground and flew up again, and the Merlin forced it
638
ShortCommunications
[Auk, Vol. 102
down a few metersfarther on. The harrier caughtup
with them and captured the blackbird on the ground,
where it restedwith its prey asthe Merlin flew away.
The harrier then flew up without the blackbird
a longer distance;(3) hiding from kleptoparasitesis
difficultor impossible;and (4) prey itemscanbe found
easily after they are relinquished by the host. The
following observationssupporteachof theseconclu-
and landed a short distance away, and an adult Red-
sions.
tailed Hawk (Buteojamaicensis)
landed on the blackbird a few secondslater. The harrier presumablysaw
the other hawk approaching and relinquished its
prey. The Red-tailedHawk restedon the ground for
a few minutes, but then it also flew up with the
blackbirdas two CrestedCaracaras(Polyborus
plancus)
(1) Kleptoparasitescan observe and follow hosts
more easily in open habitats. African Fish Eagles
(Haliaeetus
vocifer)were important kleptoparasiteson
Goliath Herons (Ardeagoliath,Mock and Mock 1980),
and it may have been the eagles' ability to observe
several hunting herons simultaneously that made
arrived from a distant palm clump and began to dive
food stealing a successfulstrategy (S. Carroll pers.
at it. The Red-tailed Hawk was joined by another comm.). In Washington I have observed most miRed-tailed Hawk, possibly its mate, and they flew
grant Parasitic Jaegers (Stercorariusparasiticus)near
away with the blackbird, the caracarasin pursuit. The
flocksof their host species,Bonaparte'sGulls (Larus
two hawks and the pair of caracarasrepeatedlydived philadelphia)and Common Terns (Sterna hirundo).
at one another in flight until the Red-tailed Hawk
LaughingGulls (Larusatricilla)and Heermann'sGulls
with the blackbird landed about 1 km from the cap- (Larusheermanni)follow Brown Pelicans (Pelecanusocture site and the caracarasflew away. I had lost sight cidentalis)
as the pelicansforage and attempt to take
of the second Red-tailed Hawk, the harrier, and the
prey from each successfulpelican (Anthony 1906,
Merlin by that time.
Schnell et al. 1983). Similarly, I watched six LaughThis interactioninvolved six raptorsof four species ing Gulls follow two Great Egrets(Casmerodius
albus)
for about 10 min. The first three specieswere vying
that were foragingon a sandflat in Florida. Although
for possession
of the prey, but the caracarasmay have I did not observe the egrets capture prey, it seemed
been displaying interspecific territoriality (Newton
clearthat the gulls were attending the egretsfor pos1979: 45) or aggressiontoward potential predators. sible kleptoparasitism.
Caracarasmay nestduring Novemberin Florida(Kale
(2) Kleptoparasitescan observe prey capture and
1978), and the catholic food habits of Red-tailed carryingmore easilyin open habitats.The Red-tailed
Hawks (Craigheadand Craighead1956) make them Hawk that took the blackbird from the harrier (dis-
possiblepredatorsof nestlings.All of theseraptors cussed above) was not visible to me when the interhave been reported as kleptoparasites(Brockmann action began and seemingly flew from a distance,
and Barnard 1979). Most reportsof kleptoparasitism perhapsbeginning its approachas the Merlin chased
involve two species,but Bent (1938: 133) cited a rethe blackbird.Similarly, I have seenParasiticJaegers
port of a crow (Corvussp.) taking a mouse from a that were in cruising flight suddenly accelerate to
Northern Harrier and losing it to a CrestedCaracara. harassa gull or tern with prey as far as 0.5 km away.
The successionof interspecific interactions proba- Clearly, the visibility of prey is directly related to
bly wasdeterminedby size,with the Red-tailedHawk
the opennessof a specifichabitat, an important vari(1,220 g) dominant to the Northern Harrier (530 g), able to birds with long-distancevision.
which was dominant to the Merlin (215 g; mean fe(3) Hostsare lessable to hide from kleptoparasites
male weights from Newton 1979). Birds are not the in open habitats.Furhess(1978) found that Parasitic
primary prey of either Red-tailedHawks or harriers Jaegerswere more successful
in taking prey from a
(Craigheadand Craighead 1956);therefore, pursuit speciesof gull and a speciesof tern (33-44% of chases
by the Merlin and capture by the harrier made the successful)
than from three speciesof alcidsthat could
blackbird more accessibleto the larger species.The
rapid reactionof the larger raptorsindicatesthat avian predatorsare often aware of the activitiesof other
predators.
Brockmann and Barnard (1979) enumerated six
ecologicalconditions facilitating the evolution of
kleptoparasitism:
(1) largeconcentrations
of hosts;(2)
large quantities of food; (3) large, high-quality food
items; (4) predictable food supply; (5) food visible;
and (6) shortageof food. I believe their "food visible" conditionis a consequence
of another important
condition, the opennessof the habitat in which both
the host and the parasitelive. The opennesscondition has four effects: (1) potential and actual hosts
can be watched, even continuously, at a longer distance;(2) capture and carrying of prey is visible for
dive to escape(11-21% successful).The ability of the
host to "hide" was important in determining the successof these kleptoparasiticattempts.Similarly, Atlantic Puffins (Fraterculaarctica)gave up their prey in
51% of kleptoparasiticattempts by ParasiticJaegers
when flying over land and only 22% of similar attempts when above the sea, where they could dive
or descendto the surface(Andersson 1976). I rarely
saw an intended host escape with its prey during
many observationsof Parasiticand Pomarine (Ster-
corarius
pomarinus)
jaegerskleptoparasitizing
gullsand
terns at sea. These birds can neither
dive below
the
surfacenor escapeto the relative safetyof a breeding
colony.For the majorityof theseobservations,only
thosebirds that swallowedprey during the chasewere
able
to retain
it.
July1985]
Short
Communications
639
anthracinus,
Buteo
nitidus,
B.lineatus,
B.platyp(4) Relinquishedprey items can be found by klep- teogallus
and B. albonotatus.
The difference
toparasitesmore easily in open habitats.Andersson terus,B. brachyurus,
(1976) observed that Parasitic Jaegerssecured 15 of betweenthesetwo groupsis significant(Fisher'sex18itemsdroppedby AtlanticPuffins.AlthoughI have act test, P = 0.01).
I believe the observationspresentedhere support
few recorded data, my impressionafter many years
of watching jaegerswith their many host speciesis what is an intuitively reasonablehypothesis,even
by humansbeingableto
that prey items droppedby hostsare rarely lost by thougha biasis introduced
interactions
moreeasilyin open
jaegers.Most fish probablyare disabledduring the detectkleptoparasitic
time it takes the parasite to force the host to drop terrain.
I thank Greg Butcher,ScottCarroll,Gary Schnell,
them and are unlikely to escapethe parasite. This is
certainlytrue for a fish carried by a bird to feed its and an anonymousbut excellentreviewerfor their
constructivecommentson the manuscript.Preparing
young.
this note has impressedon me the value of preserv"habitataswell asthe behaviorof the hostmayaffect ing field notes;without mine from 23 yearsago I
its chancesof being parasitized," but they did not would not have had thesenew thoughtson the subspecifyopennessof habitatand overwaterforaging ject.
as important considerations.Further, they suggested
Brockmann and Barnard (1979: 494) stated that
that "mixed coloniesof fishing birds provide the ideal environment for kleptoparasitismwith a plentiful
LITERATURE
supplyof food itemswhich are easilystolen"(Brockmann and Barnard 1979: 498) but did not mention
ANDERSSON,
g.
CITED
1976. Predation and kleptoparasi-
that the majorgroupsof marinekleptoparasites
(frigtismby skuasin a Shetlandseabirdcolony.Ibis
atebirds,jaegers,and gulls) often display this behav118: 208-217.
ior while away from thesecolonies.This is a reason- ANTHONY,g.W. 1906. Random notes on Pacific coast
ableoversight,becausethe best-knownkleptoparasite,
gulls. Auk 23: 129-137.
the ParasiticJaeger,has been studied at seabirdcol- BENT,A. C. 1938. Life histories of North American
onies in the north Atlantic
rather than in the north
Pacific,where it is a predatoron its breedinggrounds
(Maher 1974) and a kleptoparasite at sea.
Although mostseabirdsuse open habitats,raptors
also can be used to test the hypothesisthat openness
of habitat is an important factor leading to kleptoparasiticbehavior. The prediction is that raptors of
open country are likely to be kleptoparasiteswhile
those of woodland are not. I used the list of kleptoparasitic raptors presentedby Brockmannand Barnard (1979), with the addition of Falcosparveriusas a
kleptoparasite(S. Carroll pets.comm.),to testthe hypothesis.The categorizationis my own, basedon extensive experiencewith all specieson the list and
information summarized by Brown and Areadon
(1968). Of 22 North American falconiforms that forage primarily in open country, t0 (marked with asterisks) are known to be kleptoparasites: Coragyps
atratus,Cathartesaura*, Gymnogypscalifornianus,
Pandion haliaetus,Elanuscaeruleus,Rostrhamussociabilis,Ic-
birdsof prey. Order Falconiformes
(part 2). U.S.
Natl.
Mus. Bull.
170.
BROCKMANN,
H. J., & C. J. BARNARD. 1979. Klepto-
parasitismin birds.Anita. Behav.27: 487-514.
BROWN,L., & D. AMADON. 1968. Eagles,hawks and
falcons of the world. New York, McGraw-Hill.
CRAIGHEAD,
J. J., & F. C. CRAIGHEAD,
JR. 1956. Hawks,
owls and wildlife. Harrisburg, Pennsylvania,
Stackpole Co.
FURNESS,
R. W. 1978. Kleptoparasitism by Great
Skuas(CatharactaskuaBrunn.) and Arctic Skuas
(Stercorarius
parasiticus
L.) at a Shetland seabird
colony.Anita. Behav.26: 1167-1177.
KALE,H. W., II. (Ed.). 1978. Rare and endangered
biota of Florida. Vol. 2, Birds. Tallahassee, Florida Game & Fresh Water Fish Comm.
MAHER,W.J. 1974. Ecologyof Pomarine, Parasitic,
and Long-tailedjaegersin northern Alaska.Pacific Coast Avifauna
No. 37.
MOCK,D. W., & K. C. MOCK. 1980. Feeding behavior
tinia mississippiensis,
Haliaeetusleucocephalus*,
Circus
and ecologyof the Goliath Heron. Auk 97: 433cyaneus*,Parabuteo
unicinctus,
Buteoswainsoni,
B. albi448.
caudatus,
B. jamaicensis*,
B. regalis,B. lagopus*,Aquila NEWTON,I. 1979. Population biology of raptors.
chrysaetos,
Polyborus
plancus*,Falcosparverius*,F. coVermillion, South Dakota, Buteo Books.
lumbarius*,F. peregrinus*,
F. rusticolus,
and F. mexica- SCHNELL,G. D., B. L. WOODS, & B. J. PI,OGER. 1983.
nus*. However, none of the following 10 species,
Brown Pelican foraging successand kleptoparawhich forage primarily within forest and woodland
sitismby Laughing Gulls. Auk tOO:636-644.
in the same region, displays this behavior: Elanoides
forficatus,
Accipiterstriatus,A. cooperil,
A. gentills,Bu- Received18 June1984, accepted23 December1984.