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Singing for Your Supper: Acoustical Luring of Avian Prey by Northern Shrikes



Northern Shrikes (Lanius excubitor) are of St. Albans) and again in the last century that North- predatory songbirds in which both sexes sing much ern Shrikes may attract small passerines within at- of the year. I experimentally tested the hypothesis tack range by imitating their calls and portions of that winter singing by Northern Shrikes serves the their songs (Witchell1896, Armstrong 1973). Results purpose of attracting small passerines to be captured of such imitation have not been documented. I tested as prey. I broadcast Northern Shrike song for 5 min the premise that the winter song of Northern Shrikes while recording the number of small passerines that could serve a purpose beyond territory advertizement approached the tape player, time taken for approach and mate solicitation; namely, that it may lure po- to occur, nearest approach, and mean number of call tential prey (i.e., small passerines) within close prox- notes given by each small passerine observed. A imity. blank tape and the song of American Robin (Turdus migratorius) were controls. Treatment effect was sig- METHODS nificant for number of passerines observed, time To test the effect of Northern Shrike song on attraction taken for approach, and near~st approach, but not.for of potential prey, I applied three treatments: shrike = the number of call. notes given by each pa~senne. 5 min of Northern Shrike song; robin = 5 miD of More small .passennes were observt;:d dunng the American Robin (Turdus migratorius) song; and con- Northe~ Shrike song and these songbirds responded trol = 5 min of blank tape to control for mechanical ~ore quickly and appro~ched more closely than dur- noises involved in playback. Each treatment was fol- mg the control and ~obm treatments. ~ese results lowed by a 2.5 min "cleansing" period during which s.upport the hypothesIs that Northern Shnkes acous- no treatment occurred at the site before the subsequent tIcally lure prey.
The Condor 99:203-206
0 The
Ornithological Society 1997
Raptor Research Center, Boise State University, Boise, ID 83725
Northern Shrikes (Lanius
excubitor) are
predatory songbirds in which both sexes sing much
of the year. I experimentally tested the hypothesis
that winter singing by Northern Shrikes serves the
purpose of attracting small passerines to be captured
as prey. I broadcast Northern Shrike song for 5 min
while recording the number of small passerines that
approached the tape player, time taken for approach
to occur, nearest approach, and mean number of call
notes given by each small passerine observed. A
blank tape and the song of American Robin
were controls. Treatment effect was sig-
nificant for number of passerines observed, time
taken for approach, and nearest approach, but not for
the number of call notes given by each passerine.
More small passerines were observed during the
Northern Shrike song and these songbirds responded
more quickly and approached more closely than dur-
ing the control and robin treatments. These results
support the hypothesis that Northern Shrikes acous-
tically lure prey.
Key words: Northern Shrike,
Lanius excubitor,
foraging, singing, acoustical luring, avian prey.
The production and function of song in birds has long
been a field of great interest. Singing has been shown
to serve multiple functions including acquisition and
maintenance of mates and territories, maintenance of
social structure, and synchronization of breeding ac-
tivities. Northern Shrikes (Lanius
tain breeding and nonbreeding territories, and facili-
tate pair formation through winter singing (Miller
1931, Bent 1950, Atkinson 1991, 1993). Both sexes
sing (Miller 1931, Atkinson 1991). The winter song
of this species has been described as mimetic and is
quite variable. The repertoire consists of warbles,
trills, bzeeks, rattles, and whining calls similar to
begging and alarm vocalizations (Miller 1931, Bent
1950, Cade 1962, Atkinson 1991). In fact, portions
of the winter songs are quite reminiscent of the alarm
vocalizations given by chickadees
spp.) and
spp.) (pers. observ.).
It was suggested more than 500 years ago (Bake
Received 3 May 1996. Accepted 5 November
Present address: Hawk Mountain Sanctuary As-
sociation, 1700 Hawk Mountain Rd., Kempton, PA
19529, e-mail:
of St. Albans)
and again in the last century that North-
em Shrikes may attract small passerines within at-
tack range by imitating their calls and portions of
their songs (Witchell 1896, Armstrong 1973). Results
of such imitation have not been documented. I tested
the premise that the winter song of Northern Shrikes
could serve a purpose beyond territory advertizement
and mate solicitation; namely, that it may lure po-
tential prey (i.e., small passerines) within close prox-
To test the effect of Northern Shrike song on attraction
of potential prey, I applied three treatments: shrike =
5 min of Northern Shrike song; robin = 5 min of
American Robin
(Turdus migrutorius)
song; and con-
trol = 5 min of blank tape to control for mechanical
noises involved in playback. Each treatment was fol-
lowed by a 2.5 min “cleansing” period during which
no treatment occurred at the site before the subsequent
treatment was applied. I performed field work during
the morning hours in March and early April 1994.
I played six unique treatment sequences (control,
shrike, robin; control, robin, shrike; shrike, robin,
control; shrike, control, robin; robin, shrike, control;
and robin, control, shrike) to control for order of pre-
sentation (Milliken and Johnson 1992). One se-
quence was selected randomly with the roll of a die
and played at one of 18 individual sites. Each
sequence was presented a total of three times. I se-
lected sites in riparian areas near Boise, Idaho, USA
that typified areas inhabited by Northern Shrikes dur-
ing the winter (Atkinson 1993). Selecting sites only
within brushy riparian areas served to reduce envi-
ronmental variation; for example, passerine assem-
blages and vegetation were similar among sites.
To attempt to control for specific voice character-
istics of particular individuals, I used composite tapes
of more than one individual (Kroodsma 1990, 1992).
Since recordings of Northern Shrike songs are rare,
the Northern Shrike tape contained a composite of
the songs of two different individuals; one from the
local area (15 km southeast of the study area, March
1990) and one from Alaska (Cornell Laboratory of
Natural Sounds). The American Robin song con-
tained portions of two songs taped locally. Tapes
were played at 80% of maximum volume on a Bell
and Howell Model 3179A portable cassette player.
This level approximated the normal volume of a sing-
ing Northern Shrike as heard from 20-30 meters.
From a hidden position, I recorded the following
response variables during the 5 min of playback of
each tape: number of small passerines observed
within 15 m of the speaker, time (set) until a small
passerine first approached to within 15 m of the
speaker, nearest approach (m) to the speaker, and
mean number of calls given per small passerine dur-
ing each treatment. I tallied a small passerine” when
an individual of a potential prey species [birds as
small or smaller than a European Starling
(Atkinson and Cade 1993)] was observed
within a 1.5 m radius of the speaker. After the treat-
ment sequence, I measured nearest approach dis-
tances to the nearest 0.5 m with a field tape mea-
I square-root transformed all variables to approxi-
mate normal distributions. Neither multicollinearity
nor singularity between response variables was
present. I applied multivariate analysis of variance
(MANOVA) to test for effects of order of song pre-
sentation and carry-over effects of one sequence to
another (PROC GLM, SAS Institute 1989, Milliken
and Johnson 1992). When both carry-over and order
of presentation effects were nonsignificant, I pro-
ceeded with analysis of variance (ANOVA) to assess
the significance of treatment effects. I subsequently
contrasted Northern Shrike with other treatments
(American Robin and control tape) using a
ear contrasts within PROC GLM.
I observed Cedar Waxwings
(Bombycilla cedrorum),
European Starlings, Dark-eyed Juncos (Bunco
Song Sparrows
(Melospiza melodia),
White-crowned Sparrows
(Zonotrichia leucophrys),
American Goldfinches
(Carduelis tristis),
Siskins (C. pinus), and House Finches
during the experiment. Individuals of
these species are eaten by Northern Shrikes (Cade
1967, Atkinson and Cade 1993). During this experi-
ment, small passerines approached as individuals,
never arriving in flocks owing to the early spring tim-
ing of the field work.
Order of song presentation and carry-over effects
were not signif&t (MANOVA; Wilks Lambda =
F ?nTc; =
P =
0.43. and Wilks
G1,, I “.”
Lambda = 0.20,
F4,,8,.5 =
P =
0.38, respec-
tively), so each univariate ANOVA could be inter-
preted directly. Treatment had a significant effect on
number of passerines observed
(F,,,, =
P <
O.Ol), time taken for approach
(F,,,, =
P =
0.03), and nearest approach
(F,,,, =
P <
but not on the mean number of call notes given by
each passerine
(F,,, = 1.2, P =
0.34). I observed
more small passe&es during the Northern Shrike
song (F,,, = 15.8,
P <
O.Ol), and these songbirds
responded more quickly
- 6.0,
P =
0.03) and
approached more closely (F -
, 5 =
P <
than during the control and robin treatments (Fig. 1).
Each passerine, however, did not vocalize at a greater
rate during the shrike song than during the other
(F,,, =
P =
0.43). These pairwise
comparisons refer only to the
a priori
linear contrasts
tested between shrike song treatment and “other”
(control and robin) treatment.
I demonstrated for the first time that the song of
Northern Shrikes lures avian prey, a function be-
yond serving as mate solicitation and territory adver-
tisement (Cade 1962, 1967, Atkinson 1993). More
small passerines approached the source of the shrike
song, these songbirds came more quickly, and
approached more closely than during American
Robin and control treatments. Small passerines can
make up a significant portion of the winter diet of
Northern Shrikes especially in areas with extended
snow cover (Atkinson and Cade 1993, unpubl. data);
therefore, luring such birds into proximity may in-
crease opportunities for prey capture (Cade 1962,
Denson 1979).
Shrikes are not alone in their capacity for attract-
ing prey species. Higuchi (1986, 1988a, 1988b) and
Preston et al. (1986) described bait-fishing by Green-
backed Herons
(Ardeola striata).
Through this
method, individual herons generally employ the use
of manmade articles, twigs, or live insects placed
upon the waters surface to attract small fish to within
striking distance. Smith (1969) described a technique
by which forest falcons
spp.) attracted
avian prey. Like shrikes, these predators perch hid-
den in vegetation while giving calls that seem to at-
tract passerines searching out the source of the calls.
Smith observed three attacks resulting from such be-
havior. Pollard (1930) noted that Australian Grey
(Cracticus torquatus)
appeared to
mimic vocalizations of prey species, thereby attract-
ing these birds. Finally, Great-homed Owls
(Polyboroides typus),
Northern Harriers
(Circus cyaneus)
exploit mobbing
as potential hunting techniques (Dens& 1979, Thu-
row and Black 1981, Bildstein 1982). However. be-
cause small passerines in my experiment did not emit
alarm calls at high rates and approached shrike songs
as rapidly as they approached control tapes, it appears
that they were more inquisitive regarding the source
of the vocalizations, rather than perceiving the shrike
song as an indication of danger and as a predator to
Both male and female Northern Shrikes sing in
winter from exposed territory-advertisement perches
as well as from perches low and hidden in brushy
vegetation (Miller 1931, Bent 1950, Olsson 1984, At-
kinson 1991, 1993). It is during the latter instances
that luring of passerine prey may be most effective.
Songbirds tend to flit about in such situations
attempting to search out the singing shrike. In four
natural instances, I observed shrikes seizing these
moments to make attacks, two of which were suc-
cessful. In each case, I observed a Northern Shrike
singing that was then surrounded by small flocks of
passe&es (Dark-eyed Juncos, American Gold-
finches, and Pine Siskins). Some individuals ao-
proached to within 1 m of the shrike during each in-
stance. After several moments, each shrike suddenly
stopped singing, causing all vocalizing by the small
passerines to cease. At this time the shrikes flew
swiftly and directly at the prey, capturing an Ameri-
can Goldfinch on one occasion and a Dark-eyed
Junco on another. Further study may be able to iden-
120 -
110 -
100 -
90 -
Z -
m 80 :
$j 70 -
s 60:
F4 50 -
2 40 -
30 -
20 -
IO -
FIGURE 1. (a) Number of small passerines observed during each treatment, (b) time (set) before initial
observation of a small passerine during each treatment, and (c) nearest approach (m) to the tape player made
by a small passerine during each treatment. All responses were recorded within a 15 m radius centered on
the tape player. Means ? SE.
tify how commonly Northern Shrikes employ this
method of hunting in addition to describing which
portion of the song elicits these responses and
whether specialized vocalizations (i.e., mimicry) are
I thank L. Bond, J. Belthoff and J. Munger for sta-
tistical advice. The reviews of M. L. Atkinson, T. Bal-
gooyen, M. Beecher, J. Belthoff, R. Gerhardt, C.
Haas, W. Koenig, P. Stoddard, and three anonymous
reviewers are greatly appreciated. I thank the World
Center for Birds of Prey (The Peregrine Fund) for
providing office space while this study was per-
ARMSTRONG, E. A. 1973. A study of bird song. Do-
ver Publications, New York.
ATKINSON, E. C. 1991. Winter ecology of Northern
Shrikes (Lanius
in Idaho: foraging,
territories, and niche overlap with American
Kestrels (F&o
M.Sc. thesis, Boise
State Univ., Boise, ID.
ATKINSON, E. C. 1993. Winter territories and night
roosts of Northern Shrikes in Idaho. Condor
T. J. CADE. 1993. Winter for-
aging and diet of Northern Shrikes in Idaho.
Condor 95528-535.
BENT, A. C. 1950. Life histories of North American
wagtails, shrikes, vireos, and their allies. U.S.
Natl. Mus. Bull. 197.
BILDSTEIN, K. L. 1982. Responses of Northern Har-
riers to mobbing passerines. J. Field Omithol.
CADE, T. J. 1962. Wing movements, hunting, and
displays of the Northern Shrike. Wilson Bull.
CADE, T. J. 1967. Ecological and behavioral aspects
of predation by the Northern Shrike. Living Bird
CATCHPOLE, C. K. 1982. The evolution of bird
sounds in relation to mating and spacing be-
havior, p. 297-319. In D. E. Kroodsma, E. H.
Miller and H. Ouellet [eds.], Acoustic commu-
nication in birds, Vol. I. Academic Press, New
R. D. 1979. Owl predation on a mobbing
crow. Wilson Bull. 91: 133.
HIGUCHI, H. 1986. Bait-fishing by the Green-backed
(Ardeolu striatu)
in Japan. Ibis 128:285-
HIGUCHI, H. 1988a. Bait-fishing by Green-backed
Herons in south Florida. Florida Field Nat.
HIGUCHI, H. 1988b. Individual differences in bait-
fishing by the Green-backed Heron
associated with territory quality. Ibis
KROODSMA, D. E. 1990. Using appropriate experi-
mental designs for intended hypotheses in song
playbacks, with examples for testing effects of
repertoire sizes. Anim. Behav. 40: 1138-l 150.
KROODSMA, D. E. 1992. Much ado creates flaws.
Anim. Behav. 44:58G582.
MILLER, A. H. 193 1. Systematic revision and natu-
ral history of the American shrikes (Lanius).
Univ. Calif. Publ. Zool. 38: 1 l-242.
D. E. JOHNSON. 1992. Analysis
of messy data, Vol. I: designed experiments.
Chapman and Hall, London.
OLSSON, V. 1984. Varfagelns
Lank excubitor
tervanor. I. Biotop. Var Fagelvarld 43: 113-124.
C. MOSELEY. 1986.
Green-backed Heron baits fish with insects. Wil-
son Bull. 98:613-614.
POLLARD, J. 1930. Whisper songs. Emu 30:62-63.
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version 6, 4th ed., Vol. 2. SAS Institute, Inc.,
Cary, NC.
SMITH, N. G. 1969. Provoked release of mobbing-a
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The Condor 99:206-210
The Cooper Ormthological Society 1997
Department of Biology, Colby College, Waterville, ME 04901,
Videotapes of migrant Semipalmated
Sandpipers foraging in the upper Bay of Fundy were
analyzed to test for foraging behaviors sensitive to
prey density. Over a range of prey densities, both the
number of steps set- and probes set- increased
with increasing prey density. However, the number
of steps between probes was constant over the range
of prey densities observed. The average angle of di-
rectional change during foraging and the number of
turns mini were constant despite large differences
in prey patchiness.
Key words: Semipalmated Sandpiper,
Calidris pu-
foraging behavior, stop-over area, migration,
Buy of Fundy,
Corophium volutator.
Ornithological studies have contributed much to the
development of foraging theory (e.g., Tinbergen,
1967, Davies, 1977, Krebs et al., 1977, Zach and
Falls, 1977). However, the foraging behavior of
many birds confounds testing many predictions be-
cause birds may be difficult to observe continuously
for extended periods, may take a diverse array of prey
and may thwart efforts to quantify their behaviors be-
cause of their rapid movements. In this contribution,
Received 11 July 1996. Accepted 25 October
we explore the relationship of prey density and prey
patchiness (measured by coefficient of variation) on
foraging behavior of Semipalmated Sandpipers
(Calidris pusilla)
which essentially prey on a single
species in the upper Bay of Fundy. The high visibil-
ity and confiding nature of these shorebirds allowed
us to videotape foraging behavior at close range, per-
mitting the acquisition of data on foraging behavior
that cannot be gathered for many avian species.
These data are used to test predictions of the rela-
tionship of foraging behaviors to prey density and
prey patchiness.
Many scolopacid sandpipers, including Semipal-
mated Sandpipers, undertake migrations between arc-
tic breeding grounds and subtropical or tropical win-
tering areas. The distances of these migrations place
extraordinary energetic demands on the birds. In addi-
tion, shorebirds have higher metabolic rates than ex-
pected based on other birds of similar mass (Kersten
and Piersma 1987). It is reasonable to expect that there
should be strong selective pressure to maximize food
intake at stop-over areas during migration.
Semipalmated Sandpipers nest in the low- to mid-
arctic (Harrington and Morrison 1979, Gratto-Trevor
1992). After nesting, the majority of central and east-
em Canadian breeding birds wend their way to the
upper Bay of Fundy. During an average stay of 15
days (Hicklin 1987), the sandpipers feed primarily on
the abundant amphipod crustacean,
Corophium volu-
(Hicklin and Smith 1979). These sandpipers
... For example, predatory northern shrikes mimic the songs of prey bird species, and may use these imitations to lure prey to their deaths [2]. Spectacled parrotlets produce short contact calls that indicate both their individual identity and their group membership, and this call rapidly changes when they switch groups [3,4]. ...
... By contrast, we will be permissive with regard to proposed functions, because, in many cases, only one or a few species appears to make use of learned vocalizations in a particular manner, and the evidence for a putative function could often use improvement. For example, the imitation of prey species vocalizations by a predator as a 'lure', is firmly known only for humans, and hypothesized in one songbird species (northern shrikes [2]). We hope to inspire further work on some of these less-studied functions and species. ...
... Both sexes sing through the year for the functions of attracting mates, facilitating pair formation and defending territory, and (like many shrikes) their songs include clear examples of vocal mimicry (heterospecific imitation). Playback of shrike song attracted small passerine birds significantly more than control song (American robin) or silence [2]. This is consistent with the hypothesis that northern shrikes have evolved a novel function for vocal learning-to lure avian prey via mimicry-but more research is clearly needed to support this hypothesis. ...
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The capacity to learn novel vocalizations has evolved convergently in a wide range of species. Courtship songs of male birds or whales are often treated as prototypical examples, implying a sexually selected context for the evolution of this ability. However, functions of learned vocalizations in different species are far more diverse than courtship, spanning a range of socio-positive contexts from individual identification, social cohesion, or advertising pair bonds, as well as agonistic contexts such as territorial defence, deceptive alarm calling or luring prey. Here, we survey the diverse usages and proposed functions of learned novel signals, to build a framework for considering the evolution of vocal learning capacities that extends beyond sexual selection. For each function that can be identified for learned signals, we provide examples of species using unlearned signals to accomplish the same goals. We use such comparisons to generate hypotheses concerning when vocal learning is adaptive, given a particular suite of socio-ecological traits. Finally, we identify areas of uncertainty where improved understanding would allow us to better test these hypotheses. Considering the broad range of potential functions of vocal learning will yield a richer appreciation of its evolution than a narrow focus on a few prototypical species. This article is part of the theme issue ‘Vocal learning in animals and humans’.
... Displaying some form of delayed gratification, these birds are known to use a lure such as bread, feathers, or insects to attract more desirable prey to the edge of the water. The second case comes from the relatively asocial shrikes (family Laniidae), which have been reported as far back as medieval times to vocally mimic their prey (Atkinson, 1997). Writing about shrikes in 1575, the English poet Turberville noted, She will stand at perch upon some tree or poste, and there make an exceedingly lamentable crye. . . . ...
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... Most studies concerning ecology and sound have focused on the animal world (e.g., Farina and Pieretti 2014;Owren, Rendall, and Ryan 2010;Richards and Wiley 1980;Wiley and Richards 1978), with a large body of work on birds (e.g., Atkinson 1997;Kirschel et al. 2009;Morton 1975;Naguib and Wiley 2001;Nelson and Stoddard 1998;Smith et al. 2013) and bats (e.g., Schnitzler, Moss, and Denzinger 2003), but also dealing with other animals in aquatic (e.g., Janik 2013; Marcoux, Auger-Méthé, and Humphries 2012;Rekdahl et al. 2013) and land-based environments (e.g., Bormpoudakis, Sueur, and Pantis 2013;Rasoloharijaona et al. 2006). In terms of sound tools used to modify or enhance sound signals, primates have been documented using materials to create sound in various contexts, including the use of leaves by orangutans to lower the frequency of distress calls (e.g., Lameira, Hardus, and Wich 2012) and chimpanzee percussion of tree buttresses for producing long-distance low-frequency sound (e.g., Arcadi, Robert, and Mugurusi 2004), where higher frequency sounds are ineffective because they are attenuated by vegetation. ...
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Sound is a crucial component of the human communicative toolkit; however, as a topic of research, it has been relatively neglected in archaeological method and theory. We propose that a framework requires to be developed in which inferences can be made about the significance of sound in the past that are not bounded by the particularities of current cultural contexts. Such a framework should be multidisciplinary and draw on what is known scientifically about human sensitivities to and uses of sound, including nonverbal vocalizations, speech and music, ethological studies that offer insight into how sound perception and environment affect sociality and survival, and the effects of environment on socially significant human sound. Human sociality involves complex and dynamic relationships with sound. Not only does sound provide information about the environments in which people live (Truax 1999), but its construction, perception, and socially ascribed meanings influence how people interact with each other (Cross and Woodruff 2009). Both intentional and unintentional sounds affect how people engage with, transform, and create environments or places. This is true for communicating through spoken language, dancing, music-making, and signaling, in addition to the everyday sounds of preparing and eating food, creating tools, and moving through spaces. The social values that are ascribed to sound involve intricate and diverse world-views that are integral to modern-day societies (Atkinson 2007) and were undoubtedly significant in prehistoric and evolutionary time frames (Bannan 2012; Conard, Malina, and Münzel 2009; d'Errico et al. 2003; Mithen 2005; Morley 2013; Scarre and Lawson 2006; Wallin, Merker, and Brown 2000). However, research in this area has largely remained underdeveloped in the discipline of archaeology relative, at least, to the study of other aspects of culture, structure, and practice. In part, this has been due to the perceived ephemerality of sound and the concomitant inaccessibility of its social significance , and because there is no single discipline that can
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Vocal learning is an ability that has only evolved in a handful of taxa. Songbirds learn their songs, and some species have flexible learning in which they not only incorporate species-specific sounds, but heterospecific and/or environmental sounds as well. The functions of vocal mimicry are still unknown for many species and studying mimicry can teach us about the variation within the song learning process. In this thesis, I focused on five hypotheses on how mimicry could function in sexual selection. The repertoire size hypothesis suggests that selection for larger repertoire sizes allows mimicry to occur because imitation can increase repertoire size. The permissive learning hypothesis states that heightened song complexity requires a relaxed song template, which may allow passive use of mimicry. The learning and performance hypothesis suggests that learning ability and song or performance quality are honest signals of a singer’s quality and that listeners may focus on mimicry to assess individuals. The fourth and fifth hypotheses, which have received very little attention, are the structural function and acoustic function hypotheses, which suggest that mimicry has an as-yet-unknown structural or acoustic role in song, respectively. In these cases, mimetic accuracy does not matter; rather imitations and species-specific vocalizations are used in different ways. I explored these hypotheses using European starling (Sturnus vulgaris) song. Instead of testing the evolutionary functions of mimicry directly, I concentrated on the structural mechanics of mimicry in song. This approach allowed me to indirectly test whether mimetic and nonmimetic song components have the same functional effect. Chapter I is an overview of the more than 300 songbird species that are vocal mimics and shows that mimicry evolved repeatedly throughout the evolution of the songbird clade. The next three chapters are a detailed case study of the vocal mimicry of European starlings. In chapters II through IV, I use a combination of structural and acoustic analyses to emphasize the ways in which mimicry functions in starling song. I show that mimicry is treated differently from species-specific sounds, although in subtle, structural ways, and it remains unclear how important the inclusion of mimicry is to listeners. Advisor: Daizaburo Shizuka
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Vocal learning is an important behavior in oscines (songbirds). Some songbird species learn heterospecific sounds as well as conspecific vocalizations. The emergence of vocal mimicry is necessarily tied to the evolution of vocal learning, as mimicry requires the ability to acquire sounds through learning. As such, tracking the evolutionary origins of vocal mimicry may provide insights into the causes of variation in song learning programs among songbirds. We compiled a database of known vocal mimics that comprised 339 species from 43 families. We then traced the evolutionary history of vocal mimicry across the avian phylogeny using ancestral trait reconstruction on a dataset of oscine passerines for which vocalizations have been described. We found that the common ancestor to oscines was unlikely to mimic sounds, suggesting that song learning evolved with mechanisms to constrain learning to conspecific models. Mimicry then evolved repeatedly within the songbird clade, either through relaxation of constraints on conspecific learning or through selection for active vocal mimicry. Vocal mimicry is likely ancestral in only a handful of clades, and we detect many instances of independent origins of mimicry. Our analysis underscores the lability of vocal mimicry in songbirds, and highlights the evolutionary flexibility of song learning mechanisms.
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The biology and ecology of the Great Grey Shrike Lanius excubitor in the Thüringen Basin and the Kyffhäuser-Unstrut area. Part 2: food and foraging The composition and seasonal variation of the dietary spectrum of the Great Grey Shrike in the agricultural landscape of the Thüringen Basin during the period 1992-2008 were studied on the basis of 3423 pellets and 665 prey remains. From these, a total of 15 689 prey animals could be isolated and identified: 13 799 individual invertebrates (88 % by number) with a biomass of 3132 g (8 % by weight) and 1890 vertebrates (12 %) with a biomass of 36125 g (92 %). For the time period March to October, a prey value (following Nicolai) was calculated for each prey animal group and pentade. For the individual taxa, this varied according to seasonal prey supply and availability, as well as the physiological condition of the birds (breeding season, moult, etc.). The prey value of the invertebrates can briefly reach up to 85 %. The invertebrate share of the diet is almost negligible in the winter months, but after March rises steadily until the time just after the hatching of the young, when it is abruptly and almost completely replaced by vertebrate prey (birds and voles above all), only to rise substantially again at the end of June/beginning of July. In the first half of September invertebrate prey values of up to 85 % are attained once more. The causes of the changing dietary spectrum and the fluctuations in prey value in the course of a year are discussed. The vertebrate share of the diet is dominated by voles. Bird prey is generally limited to the time when young are being raised, but their share of the vertebrate diet can reach very high values. The number of young birds taken is clearly greater than that of adults. The invertebrate prey items are dominated, with seasonal variations, by the ground beetles (Carabidae) and the Hymenoptera. The particular importance of Carabus auratus and of bumble bees (genus Bombus) in Great Grey Shrike diet is emphasized. Some observations of prey capture techniques are described.
Distress calls are loud, harsh calls given by some species of birds when they are captured by a predator or handled by humans. We recorded the frequency of distress calls and struggling behavior in 40 species of birds captured in mist nets during the dry season in a Costa Rica cloud forest. We tested the following hypotheses proposed to explain the function of distress calls: (1) calling for help from kin or reciprocal altruists; (2) warning kin; (3) eliciting mobbing behavior; (4) startling the predator; and (5) distracting the predator through attraction of additional predators. Our results did not support the calling-for-help, warning kin, or mobbing hypotheses, Indeed, genera that regularly occurred with kin or in flocks were not more likely to call than non-flocking genera. There was no relationship between calling frequency. and struggling behavior as predicted by the predator startle hypothesis. Genera of larger birds tended to call more than smaller birds, providing some support for both the predator distraction hypothesis and predator startle hypotheses. Calls of higher amplitude may be more effective in startling the predator, Distress calls of larger birds may also travel greater distances than those of smaller birds, supporting the predator manipulation hypothesis, but this requires further testing.
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To study the winter ecology of Northern Shrikes in southwest Idaho, I observed the activities of six color-banded and six radio-tagged shrikes over the winters of 1988-1989 and 1989-1990. These shrikes occupied winter territories that averaged 216 ha in size (minimum convex polygon method). Over one-half of the activity of each shrike was confined to a core area of approximately 50 ha. Five of nine individual Northern Shrikes perched in or hunted within mesic areas significantly more than expected and four of the nine utilized grasslands significantly less than expected. Linear habitats such as riparian corridors and rimrock outcroppings appeared to be important to wintering shrikes since the former provided night roost habitat whereas the latter provided warm and productive areas for prey populations. I located 10 night roosts of Northern Shrikes. All were in deciduous shrubs with many small stems. Shrikes may depend upon these roosts for thermal protection and escape from predators.
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We observed color-banded and/or radio-tagged Northern Shrikes (Lanius excubitor) wintering in southwest Idaho and determined that foraging success of these shrikes was over 69%. Foraging success was dependent upon the type of prey attacked. Predation success upon arthropods was greater than 90%, whereas predation upon vertebrates (small mammals and passerines) was substantially lower (56% and 19%, respectively). We collected 237 pellets from 12 shrikes and identified 671 individual prey items contained in these pellets. Arthropods and small mammals were the most important prey items as measured by number (63.9% and 29.8%, respectively) and Index of Relative Importance (38.9% and 59.6%, respectively), whereas small mammals were the most important components of shrike diet by biomass contributing 83.1% of the total prey biomass. Passerines were of lesser importance in the winter diet of shrikes accounting for 11.8% of the biomass but only 1.7% of the Index of Relative Importance.
Thurow, T. L. & Black, H. L. 1981. Ecology and behaviour of the Gymnogene. Ostrich 52:25-35.Observations were made on two pairs of Gymnogenes Polyboroides typus throughout most of the 1978 breeding season. The nests were attended by at least one of the pair 98% of the daytime, with both parents participating in the 35–36 day incubation period. Changes in facial colour and exchange of nesting material were apparently stimuli necessary for cooperative nest relief. After chicks had hatched, the male returned to the nest only to deliver prey to the female. Changes in the male's facial colour also accompanied food transfers. By the fourth week the female began hunting and the male no longer approached the nest but transferred prey to her away from the nest site.Four general hunting methods were used: low soaring, high soaring, perch hunting and canopy-ground hunting. Of 85 prey items identified during this study 33% were birds (primarily nestlings), 41% reptiles and amphibians, 15% small mammals and 11% insects. Most prey can be characterized as defenceless or inactive at the time of capture.
Individual differences were found in the feeding sites, frequency of bait fishing, and fishing success in three individual Green-backed Herons in southern Japan. The differences in the use of bait fishing and in fishing success seemed to be related primarily to differences in feeding sites, which were associated with territory quality. Bait fishing was used most frequently by the individual which fished often in open water with fewer suitable rocks, where the heron has to overcome the handicap of being easily seen by fish. Bait fishing was least common in the individual which fished most often from high branches. The leaves and twigs dropped from high branches rarely reached the spot the heron intended, and the fishing success was low. Individuals probably also differed in their skill at bait fishing.
In playback experiments, a mismatch between the experimental design and the intended hypothesis often prevents the intended hypothesis from actually being tested. A review of the literature reveals, for example, that, despite numerous studies, available data do not provide a strong test of the hypothesis that larger song repertoires are especially stimulating to songbird listeners. Single exemplars are often used to represent all possible repertoires of a given size, i.e. the treatment is unreplicated. Repeated response measures to one repertoire are often then used in statistical tests as if those measures were the mean responses to different repertoires of a given size. Because studies usually do not control for variation present in successive renditions of a single song type, they test for the overall effects of ‘song variation’, not specifically for the effects of song type repertoires. Additional concerns include controls for observer-expectancy bias and re-use of either individuals or stimuli to generate inflated sample sizes. Several improved experimental designs are proposed and an increased awareness of these critical issues in experimental research in all subfields of animal behaviour is encouraged.