Conspecific Attraction and the Conservation
of Territorial Songbirds
MICHAEL P. WARD∗‡ AND SCOTT SCHLOSSBERG†
∗Department of Animal Biology, University of Illinois, Urbana-Champaign, 201 Shelford Vivarium, 606 E. Healey Street,
Champaign, IL 61820, U.S.A., email firstname.lastname@example.org
†Program in Ecology and Evolutionary Biology, University of Illinois, Urbana-Champaign, 201 Shelford Vivarium,
606 E. Healey Street, Champaign, IL 61820, U.S.A., email email@example.com
Abstract: Conspecific attraction, the tendency for individuals of a species to settle near one another, is well
described in colonial species, especially birds. Although this behavior may occur in territorial birds, evidence
has been lacking. If territorial birds do exhibit this behavior, it would have major conservation implications.
Birds could potentially be attracted to specific sites with artificial stimuli, making conservation of those species
more efficient. In 2001 and 2002, we tested whether conspecific attraction occurs in an endangered, territorial
songbird, the Black-capped Vireo (Vireo atricapilla) by playing vireo vocalizations in unoccupied habitats at
Fort Hood, Texas. We were successful in attracting 73 birds to five experimental sites in 2001 and 75 birds
to seven experimental sites in 2002. No birds settled on comparable control sites. Many birds attracted to
the vocalizations paired and bred. At most research sites the primary threat to the species, the brood-parasitic
to a nearby, unmanipulated population. Second-year birds were more responsive to conspecific vocalizations
than older birds, as they were more common on experimental sites than in the established population. In
2002 birds recolonized experimental sites from 2001 where vocalizations were not played in 2002, indicating
that 1 year of playbacks may be sufficient to establish a population. Our results provide the first experimental
evidence that territorial songbirds use the presence of conspecifics when deciding where to settle and suggest
that conspecific attraction may provide a valuable conservation tool.
Key Words: Black-capped Vireo, conspecific attraction, endangered species, habitat selection
Atracci´ on Conespec´ ıfica y la Conservaci´ on de Aves Canoras Territoriales
Resumen: La atracci´ on conespec´ ıfica, tendencia de los individuos de una especie a establecerse cerca de otro
de la misma especie, est´ a bien descrita en especies coloniales, especialmente aves. Aunque este comportamiento
puede ocurrir en aves territoriales, se carece de evidencia. Si aves territoriales muestran este comportamiento,
tendr´ ıa implicaciones mayores en la conservaci´ on. Las aves potencialmente ser´ ıan atra´ ıdas a sitios espec´ ıficos
mediante est´ ımulos artificiales, haciendo m´ as eficiente la conservaci´ on de esas especies. En 2001 y 2002,
probamos si ocurre la atracci´ on conespec´ ıfica en una especie de ave canora territorial, en peligro, Vireo
atricapilla,conlareproducci´ ondevocalizacionesdevireoenh´ abitatsdesocupadosenFortHood,Texas.Tuvimos
´ exito al atraer a 73 aves a cinco sitios experimentales en 2001 y 75 aves a siete sitios experimentales en 2002.
No se establecieron aves en sitios controles comparables. Muchas de las aves atra´ ıdas a las vocalizaciones
formaronparejaysereprodujeron.Enlamayor´ ıadelossitios,laprincipalamenazaparalaespecie,elpar´ asito
Molothrus ater, fue controlada, lo que permiti´ o un elevado ´ exito de anidaci´ on a los vireos en comparaci´ on con
una poblaci´ on no manipulada cercana. Las aves de dos a˜ nos tuvieron mayor respuesta a las vocalizaciones
conespec´ ıficas que las aves m´ as viejas, porque fueron m´ as comunes en los sitios experimentales que en la
poblaci´ on establecida. En 2002 aves recolonizaron sitios experimentales de 2001 en los que no se reprodujeron
‡Order of authorship determined by coin flip.
Paper submitted November 13, 2002; revised manuscript accepted June 4, 2003.
Conservation Biology, Pages 519–525
Volume 18, No. 2, April 2004
Conspecific Attraction in Territorial Birds Ward & Schlossberg
vocalizaciones en 2002, lo que indica que 1 a˜ no de repetici´ on de vocalizaciones puede ser suficiente para
establecer una poblaci´ on. Nuestros resultados proporcionan las primeras pruebas experimentales de que aves
canoras territoriales utilizan la presencia de conespec´ ıficos al decidir donde se establecen y sugieren que la
atracci´ on conespec´ ıfica puede ser una valiosa herramienta de conservaci´ on.
Palabras Clave: atracci´ on conespec´ ıfica, especies en peligro, selecci´ on de h´ abitat, Vireo atricapilla
Understanding an animal’s behavior may be just as impor-
tant for conservation as understanding its environment
1999; Gosling & Sutherland 2000). Traditionally, animal
populations have been conserved by identifying and con-
trolling threats such as habitat destruction or predators.
Recently, however, conservationists have recognized that
simply focusing on an animal’s external environment may
describes numerous examples of how behaviors such as
predator naivet´ e or avoidance of gaps during dispersal
have contributed to the extinction and endangerment of
standing behavioral processes may allow managers to de-
an example, behavioral training in skills such as predator
cess of animal reintroductions (e.g., Biggins et al. 1999;
McLean et al. 2000; Meretsky et al. 2000).
One of the best examples of the in situ application of
behavioral techniques is work on colonial seabird rein-
troduction by Kress (1997). Many colonial seabirds ex-
hibit conspecific attraction, a tendency to settle near in-
dividuals of their own species. To reestablish colonies
of Atlantic Puffins (Fratercula arctica) and Arctic Terns
(Sterna paradisaea) on uninhabited islands, Kress used
models of birds, mirrors, and playbacks of calls to create
the appearance of an occupied colony. As a result, birds
has been used successfully on a number of colonial bird
et al. 1997; Jeffries & Brunton 2001; Martinez-Abrain et
Although these results show promise for conserva-
tion, this technique has only been applied to birds that
breed in groups. The majority of bird species are terri-
torial (Lack 1968), and conspecific attraction has never
been demonstrated conclusively in territorial birds. In
fact, habitat-selection theory predicts that individuals of
territorial species should eschew conspecifics to avoid
density-dependent fitness losses (Fretwell & Lucas 1970).
Nonetheless, anecdotal and observational evidence sug-
gests that conspecific attraction may occur in territorial
species (Stamps 1988). Observers have reported a ten-
dency for birds to aggregate their territories, even in con-
tinuous habitat (Møller 1983; Herremans 1993; Poysa et
al. 1998; Tarof & Ratcliffe 2000; Arsenault et al. 2002).
In an observational study of nest-site selection by House
Wrens (Troglodytes aedon), Muller et al. (1997) found
that new breeders at a site select nest boxes based on
their proximity to established males’ territories. To our
knowledge, the only previous experiment on conspecific
They found that Pied Flycatchers (Ficedula hypoleuca)
are somewhat more likely (p = 0.07) to settle at sites
where vocalizations had been played than at comparable
If territorial birds use the presence of conspecifics
to determine where to settle, this behavior would have
significant conservation implications (Smith & Peacock
1990). By reproducing the appropriate cues, birds could
be attracted to specific, preselected sites known to be
high-quality habitat or managed to mitigate limiting fac-
are managed. Currently, the only option for conserving
many species is to protect existing habitat or to control
attract individuals to predetermined locations would al-
low managers to more effectively and efficiently manage
endangered or declining species.
Here, we report the results of an experimental study of
conspecific attraction in an endangered, territorial song-
bird, the Black-capped Vireo (Vireo atricapilla). This
Neotropical migrant breeds in early successional shrub-
lands over a small range in Texas and Oklahoma (U.S.A)
as well as northern Mexico (Grzybowski 1995). The
vireo is threatened by loss of habitat due to fire suppres-
sion and livestock grazing and by brood parasitism by
that vireos may select habitats based on the presence
of conspecifics because the birds are often patchily dis-
tributed and can take several years to colonize new habi-
tat (Graber 1961). We addressed four questions: (1) Do
Black-capped Vireos preferentially settle where conspe-
cific vocalizations are played? (2) Will birds attracted by
are the demographic characteristics of populations estab-
lished through conspecific attraction? (4) Do populations
Volume 18, No. 2, April 2004
Ward & Schlossberg Conspecific Attraction in Territorial Birds
Table1. Study sites and experimental design for the study of
conspecific attraction in Black-capped Vireos.
control SiteLocation2001 2002
established through conspecific attraction persist for
more than 1 year?
We selected five study sites at Fort Hood (a U.S. military
base), Texas, and two other sites on private property in
central Texas that had one or no pairs of vireos for at least
2 years before 2001. These sites ranged in size from 15 to
71 ha and were appropriate habitat for vireos based on
rich, personal communication). Fort Hood has one of the
largest populations of Black-capped Vireos, and Brown-
this location for the past 13 years (Eckrich et al. 1999).
Cowbirds were not controlled at the two sites on private
In 2001 we played recordings of vireo vocalizations at
(Table 1). Two sites, one on the base and one off, were
controls where we did not play vocalizations. In 2002 we
played vocalizations at the two control sites from 2001,
making them experimental playback sites. To determine
whether a second year of playbacks would be necessary
for vireos to recolonize experimental sites from 2001, we
did not play vocalizations at two of the five former ex-
perimental sites in 2002. At the other three experimental
sites from 2001, we conducted playbacks in the previous
Playback of Vocalizations
At each experimental site, we played prerecorded vocal-
izations of Black-capped Vireos on two to four portable
stereos (call boxes), spaced approximately 200 m apart.
Vocalizations were not played at the control sites. At the
experimental sites, vocalizations were played at maxi-
mum volume (approximately 80 db) from 0400 to 1030
daily throughout the settlement period and the breeding
season (mid-March through early July). We mounted the
stereos on wooden platforms, approximately 2 m above
the ground, and a solar panel powered the system. The
stereos played compact discs that were 74 minutes long
and included approximately 50 minutes of Black-capped
Vireo song recorded at Fort Hood, 4 minutes of vireo
nus forficatus), Painted Bunting (Passerina ciris), Field
Sparrow (Spizella pusilla), and Rufous-crowned Sparrow
(Aimophila ruficeps). We included the silent periods and
heterospecific songs to prevent the vireos from habitu-
ating to the playbacks. Vocalizations were divided into
tracks approximately 1 minute long. The stereo played
the vocalizations in random order, playing each track on
the disc once before repeating.
In 2001 we placed plastic resin models of vireos near
some call boxes. This was done because we were un-
without a visual stimulus. We never observed vireos in-
teracting with the models, and there was no difference
in settlement patterns between sites with and without
models. Consequently, we did not use models again in
We visited all sites at least once a week throughout the
breeding season and recorded the locations of all vireos
seen or heard. We monitored all sites except one control
site in 2001, when personnel from The Nature Conser-
of males by plumage characteristics (Grzybowski 1995).
Males were classified as either second-year (hatched the
previous year) or after-second-year. In addition, we cap-
tured some vireos with mist nets and banded them with a
unique combination of color bands. Where vireos estab-
lished territories and paired, we located nests and moni-
tored them at 2- to 7-day intervals.
determine the number of second-year and after-second-
year males and the number of females present. Popula-
tion estimates were based on numbers of banded birds
and simultaneous sightings of individuals, analogous to
the spot-mapping technique (Bibby et al. 2000). In 2002,
observations of previously banded vireos allowed us to
determine the return rate of individuals. We used Fisher’s
exact test to compare return rates of birds at sites with
and without cowbird control. We used the same test to
compare the age structure of males in 2002 at sites with
or not birds attracted to experimental sites behaved typ-
ically for this species, we compared the nesting success
Volume 18, No. 2, April 2004
Conspecific Attraction in Territorial BirdsWard & Schlossberg
numbers of Black-capped
Vireos on study sites.
and age structure of vireos on experimental sites with
those of an established population at Fort Hood, which
has been studied for the last 13 years (The Nature Con-
servancy 2001). We compared age structure between the
Prior to 2001, four Black-capped Vireos had been ob-
served on our seven sites over several years. In 2001 we
observed 73 vireos on five experimental sites, whereas
no birds settled on two control sites (Fig. 1). In 2002
we observed 75 vireos on the seven sites. At each site,
the first year of playbacks led to an increase in the local
vireo population relative to the previous year (Wilcoxon
signed-rank test, T = 0, p = 0.02; Fig. 1). On the two sites
that had call boxes in 2001 but no call boxes in 2002,
the number of vireos remained nearly unchanged (29 vs.
30, 3 vs. 3, respectively). The sites that had call boxes
Table2. Nesting success and brood parasitism rates of Black-capped
Vireos on experimental sites (vocalization playbacks) and a nearby,
All experimental sites (n = 33)
Fort Hood sites (n = 29)
Off-base sites (n = 4)
Established populationb(n = 132)
aEstimated using the Mayfield (1975) method for the entire nesting
period of 26 days. For experimental sites, data from 2001 and 2002
bData from The Nature Conservancy (2001).
for a second year in 2002 also continued to have similar
numbers of vireos (24 vs. 31, 3 vs. 3, 9 vs. 6).
success was similar in both years, so we combined results
fered based on whether or not cowbirds were controlled.
On sites with cowbird control, vireos had high nesting
success and low cowbird parasitism (Table 2). On the
site without cowbird control, all nests were parasitized
and unsuccessful in both years of the study (Table 2).
The nesting success of vireos on sites with cowbird con-
trol at Fort Hood was even greater than that of the estab-
lished populations (Table 2).
In 2001, 42% of the males on our experimental sites
were in their second year (n = 48). In contrast, the age
structure of males in the established population at Fort
Hood was 28% second-year (The Nature Conservancy
2001). There was a marginally significant difference in
the percentage of second-year males in the two popula-
tions (G = 3.44, p = 0.06). In 2002 at sites that had call
boxes in both 2001 and 2002, 32% of males were second-
year (n = 26). At sites where call boxes were used only
in 2001, 26% of males were second-year (n = 21). This
was not a significant difference (Fisher’s exact test, p =
Overall, 33% (n = 33) of the vireos banded as adults
(second-year or after-second-year birds) in 2001 returned
to the same sites in 2002. By sex, 41% (n = 27) of the
males and 17% (n = 6) of the females returned. A higher
proportion of males, 52% (n = 21), returned to sites with
cowbird control than to sites without, 0% (n = 6; Fisher’s
exact text, p = 0.03). This relationship did not hold for
females, 20% (n = 5) of which returned to sites with
cowbird control and 0% (n = 1) of which returned to
sites without cowbird control (Fisher’s exact test, p =
0.33). The test, however, has low power because of the
small sample size.
Volume 18, No. 2, April 2004
Ward & SchlossbergConspecific Attraction in Territorial Birds
Our results offer strong experimental evidence that ter-
ritorial birds use the presence of conspecifics to select
a habitat. Playing conspecific vocalizations invariably led
to an initial increase in local vireo populations. Although
our sample sizes were small, evidence leads us to believe
The increase in vireo numbers on experimental sites was
not due to an influx of vireos into the region. In fact, the
regional population of vireos on Fort Hood decreased be-
tween 2000 and 2001 (The Nature Conservancy 2001).
Furthermore, the vireos appeared to treat the call boxes
as if they were birds with very small territories. Early
in the season, vireos frequently counter-sang with the
call boxes. In some cases, vireos would sing while mov-
ing around the call box, a behavior reminiscent of birds’
counter-singing at the edges of one another’s territories.
Later in the season, however, the birds appeared to have
habituated to the call boxes. They no longer sang in re-
sponse to the playbacks, just as birds are known to habit-
uate to the calls of their neighbors once their territories
are established (Brooks & Falls 1975).
The playbacks consisted of both conspecific and het-
migratory birds are attracted to areas with high num-
bers of heterospecific residents when selecting habitats
(M¨ onkk¨ onenetal.1990;Forsmanetal.1998;M¨ onkk¨ onen
& Forsman 2002). Although we cannot rule out the possi-
bility that heterospecific vocalizations attracted vireos in
this experiment, we find this conclusion unlikely. The
74-minute playback disc included only 10 minutes of
heterospecific songs versus 54 minutes of Black-capped
cific song playbacks. They did, however, respond to
conspecific songs with approaches and counter-singing.
than to heterospecific vocalizations, but further experi-
ments would be necessary to confirm this conclusion.
Although vireos were attracted to playbacks in appro-
priate habitat, this does not imply that vireos could be
attracted to any type of habitat. Our results suggest that
habitat quality may be important in habitat selection by
vireos, and this may influence the success or failure of
this conspecific attraction technique. Two sites that only
attracted a few birds (sites 1 and 27 in Fig. 1) had limited
amounts of high-quality habitat surrounded by a larger
of cues used by vireos to select habitats (Stamps 2001).
Unlike colonial seabirds, which can be attracted by
models, vireos appeared to be attracted only by vocal-
izations. The vireos’ lack of a response to models may
have been due to the dense vegetation in their habitat.
This scrubby, early-successional habitat is dominated by
and vireos spend much of their time in the foliage. They
therefore probably communicate primarily through vo-
calizations. Visual cues may be more important to passer-
ines in other habitats, and models may be necessary for
conspecific attraction in these species.
Overall, vireos attracted to experimental sites behaved
similarly to vireos in natural populations. Birds on our
cowbird control, vireos had high nesting success, indicat-
ing that populations founded through conspecific attrac-
tion can be productive and contribute to the recovery of
Following removal of call boxes on two sites in 2002,
many individuals exhibited site fidelity. Presumably, these
returning birds acted as a seed for their local popula-
tions and attracted new birds to the sites (as described
by Stamps 1991). Site fidelity, however, was strongly in-
fluenced by cowbird control. In many species, individu-
als that reproduce successfully one year are more likely
to return to a site in the following year (e.g., Bollinger &
Gavin 1989; Haas 1998; Hoover 2003). On our sites that
lacked cowbird control, nesting success was extremely
low, and none of the birds banded there in 2001 returned
in 2002. In contrast, nesting success was much higher
on sites with cowbird control, and return rates were cor-
respondingly higher. This implies that populations estab-
lished with conspecific attraction would not recolonize a
site if Brown-headed Cowbirds were not controlled and
if nesting success were too low. Thus, the success of con-
specific attraction in establishing a population that per-
sists for multiple years may require high nesting success.
Populations on experimental sites in 2001 contained a
higher proportion of second-year males than did estab-
lished populations. There are two possible explanations
for this pattern. First, because they lack experience in se-
lecting breeding habitat, young birds may be more likely
than older birds to use conspecific attraction. Alterna-
specific attraction. Because some after-second-year birds
will return to their previous breeding sites, second-year
birds may simply make up a greater proportion of the
birds settling at new sites.
Implications for Habitat Selection
Theoretical and empirical studies of habitat selection
suggest that animals should avoid conspecifics because
fitness decreases with density (Fretwell & Lucas 1970;
Sinclair 1989; Newton 1998). In our study, birds be-
haved in direct opposition to this prediction. The fact
that individuals of a species are attracted to one an-
other when selecting habitat suggests that basic tenets
of habitat-selection theory—competition and density
Volume 18, No. 2, April 2004
Conspecific Attraction in Territorial Birds Ward & Schlossberg
dependence—may need to be revised to include positive
interactions among individuals (Stamps 2001).
Why would birds be attracted to one another if fitness
potential explanations, conspecific cuing and the Allee
effect. Conspecific cuing involves using the presence of
others of one’s species as an indicator of habitat quality
(Stamps 1988). Allee effects occur when fitness increases
with density (Stephens & Sutherland 1999). Our results
support conspecific cuing; the main benefit vireos ob-
tain from settling near conspecifics is the identification
of suitable habitat. As discussed above, birds often ex-
hibit site fidelity when they reproduce successfully and
disperse after failing to reproduce. Thus, the presence
of experienced individuals at a site could be an indica-
tor of high-quality habitat. As a result, a good strategy for
ritory near that of site-faithful males (Alatalo et al. 1982;
Stamps 1988, 1991). For Black-capped Vireos, site qual-
ity is primarily influenced by the abundance of Brown-
headed Cowbirds. Thus, conspecific attraction may be
an effective defense against Brown-headed Cowbirds.
Using Conspecific Attraction in Conservation
One of the most significant benefits of the technique we
tested is that it could be used to attract birds to high-
and reproduction (e.g., predators or brood parasites) are
controlled. In many cases where humans have altered
landscapes, birds may be attracted to areas where they
experience poor survival or reproductive success (e.g.,
Gates & Gysel 1978; Wilcove 1985; Robinson et al. 1995).
because birds cannot distinguish between high- and low-
quality habitat (Schlaepfer et al. 2002). For species prone
to use conspecific attraction, conservationists could use
playbacks to attract birds to settle in high-quality habitats.
due to selection of ecological traps.
vireo nesting success and site fidelity were much higher
bird control leads to higher reproductive success, it is
moderate levels of cowbird parasitism (35%), vireo popu-
1999). Thus, attracting birds to sites without controlling
cowbirds would be pointless and potentially harmful to
conservation efforts. When using conspecific attraction,
the importance of management cannot be understated.
Simply attracting birds to a new site will not provide con-
the site is known to be of high quality.
This study would not have been possible without advice
and support from T. Hayden, G. Eckrich, J. Cornelius, and
personnel from The Nature Conservancy, Fort Hood of-
fice. Funding was provided by the Fort Hood Natural Re-
sources Branch and the U.S. Army Corps of Engineers
Engineering Research and Development Center, Cham-
paign, Illinois. For outstanding assistance in the field, we
family and the staff of The Nature Conservancy’s Barton
Creek Preserve for granting us access to their sites. J.
Brawn, D. Enstrom, J. Foster, S. Robinson, K. Sieving, P.
ments that helped us improve the manuscript. S.R.S. was
search Fellowship while conducting this study.
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