| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Behavioral Ecology Vol. 12 No. 3: 295-300
© 2001 International Society for Behavioral Ecology
Perch selection by singing chaffinches: a better view of surroundings and the risk of predation
is Krams
Department of Sciences, Daugavpils Pedagogical University,
Vien
bas iela 13, LV-5400 Daugavpils,
Latvia
Address correspondence to I. Krams. E-mail: krams{at}apollo.lv .
Received 9 January 2000; revised 2 August 2000; accepted 2 August 2000.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
|---|
Predation risk varies among perches, and the vulnerability of singing chaffinches (Fringilla coelebs) might differ depending on where they perch in a tree. To find out how singing of the chaffinch is associated with antipredatory behavior, I studied perch selection in mature pine forest and in pine saplings, two habitats differing in the amount of cover for protection from predators. My results show that male chaffinches prefer to sing below the canopy of mature pines and in the uppermost parts of sapling pines. Although these are the canopy parts most exposed to sparrowhawk (Accipiter nisus) attacks, staying in open sites may be a beneficial strategy for singing chaffinches because it makes it possible to improve antipredatory vigilance. This assumption was supported by the hawk experiments. After being exposed to the sparrowhawk model, all of the singing birds selected the conspicuous perch below the canopy of mature pines. The males that perched higher in the canopy before the experiment moved to the lower canopy, whereas those males that sang below the canopy did not change their singing perch.
Key words: Fringilla coelebs, perch selection, predation risk, singing chaffinches, territorial advertisement.
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
|---|
The results of several field studies provide some support for the assumption that conspicuous, long-range calling is costly in terms of predation (Haskell, 1994
;
Leech and Leonard, 1997;
Redondo and Castro, 1992;
Ryan et al., 1982). The
elaborate displays or loud songs that many male birds use to attract a mate
and to repel other males from territories are also likely to attract predators
(Catchpole and Slater, 1995;
Lima and Dill, 1990;
Newton, 1986). Most males
reduce or even stop singing as soon as their mate begins to incubate, which,
although usually explained with reference only to the change in the female's
fertility, could also suggest a compromise between reproductive success and
danger from predation (Snow and Perrins,
1997). However, many birds continue to sing till the end of the
breeding season, and they provide excellent models for examining the costs
associated with singing.
Field experiments by Slater
(1981) showed that the song of
the chaffinch, Fringilla coelebs, has a role in the relationship
between neighboring birds and that it indicates ownership to other potential
intruders during the entire breeding season
(Snow and Perrins, 1997). Song
typically is delivered from a conspicuous perch, and the singer changes
perches regularly (Marler,
1956). These characteristics make the song conspicuous and could
attract acoustically orienting predators. Thus, singing is assumed to have a
predation cost. Direct measurements are essential to determine whether the
costs associated with singing are sufficient to decrease reproductive success.
However, it is also important to study antipredatory behavior that should be
associated with singing if singing males are indeed more at risk.
Some previous field studies have revealed that predation risk varies within
the tree and is higher for the birds that use the outer parts of branches in
the lower canopy (Ekman, 1986;
Suhonen,
1993a,b)
and the uppermost parts of young trees
(Krams, 1996). This suggests
that vulnerability of singing chaffinches might differ between different parts
of the tree. Communication theory suggests that males optimize vocal
transmission through the environment by singing at some distance above the
ground (Catchpole and Slater,
1995). Hence, height-dependent attenuation also may influence
perch selection (Marten and Marler,
1977; Wiley and Richards,
1982).
The purpose of this study was to determine how singing of the chaffinch is
associated with antipredatory behavior. I studied the selection of singing
perches in mature pine forest and pine saplings, two habitats that differ in
the amount of cover for protection from predators
(Krams, 1996). I reasoned that
there is a trade-off between territorial advertisement and the risk of
predation and that the height of the perch should be selected to maximize
singing rate at the least level of predation risk. First, I hypothesized that
singing chaffinches may select perches in dense parts of the canopy where the
risk of being preyed upon decreases because of concealment by vegetation
(Götmark et
al., 1995;
Götmark and
Post, 1996). However, from a completely concealed perch, the bird
cannot scan its surroundings for airborne predators. When changing perches, it
may be attacked by hawks, which hunt by flying from tree to tree, watching for
prey from hidden positions (Newton,
1986). Second, I hypothesized that male chaffinches may increase
singing rates from open perches, which may facilitate early detection of
predators and so decrease the risk of predation. It is important to note that
territorial males rely on their own vigilance
(Krams, 1998;
Lima, 1994) rather than
collective predator detection. To see if the view of surroundings is important
for singing chaffinches, I observed their perch selection in pine forests and
in growths of saplings.
|
METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
|---|
I collected data on the singing behavior of the chaffinch near the town of Kr
slava, Latvia. The study area consists
mainly of 60- to 70-year-old coniferous forests dominated by Scotch pine
(Pinus sylvestris) with nearly no undergrowth. Trees of this mature
forest were on average 18 ± 3.7 m (mean ± SE) high, and the
canopy portion began on average at a height of 6.5 ± 1.8 m. A number of
dead branches occur between the ground and the lowest part of the canopy.
Because of the many small, semi-open bogs and areas of saplings, the forests
are highly fragmented. In a habitat composed of about 20-year-old pine
saplings, where the lower branches have not yet been shed, every tree
resembles canopy with average height of 7 ± 0.9 m and without a
distinctive trunk. This closed structure of the lower branches provides better
shelter from airborne predators than the lower tree sections of a mature pine
habitat. Thus, in a pine sapling habitat the sparrowhawk, Accipiter
nisus, the main diurnal predator of passerines in the study area,
succeeds in its attacks on the singing birds mainly when these attacks are
initiated from above (Krams,
1996). In mature forest, sparrowhawks attack their prey both from
above and from within the lower canopy. Because predation is an important
cause of mortality in chaffinches (Newton,
1986), habitat use in saplings should be different from that in
mature forest. I observed singing birds between 0600 and 1300 h and between 1700 and 2000 h in May and early June 1998 and in April and June 1999. For each observation I estimated the perch height of the singing bird and the height of the tree. The perch heights were then expressed as proportions of canopy height and divided into four categories The perch height of the birds below the canopy was expressed as proportion of the canopy height, given a negative sign. To control for predator exposure at canopies, which might differ in shape, I also estimated the distance of the bird from the trunk and the length of the branch used. Distance from trunk was transformed to a relative distance and divided into four categories. To avoid a discovery bias, the perch and singing rate were recorded with a delay of 10 s, using an electronic metronome, between finding a bird and recording its behavior and position in the tree. To estimate singing rate, I counted number of songs each individual gave during 5 min from the same perch. To reduce statistical dependence between observations, the height of perch and singing rate of each color-banded individual was recorded only once in a day. In total, 490 observations were made of the birds (n = 70; mean number of observations per bird = 7) in mature forest and 434 observations were made of the birds (n = 70 ; mean number of observations per bird = 6.2) in saplings.
I also collected data on the foraging sites of chaffinches, and I observed 27 males in mature forest (216 total observations; mean number of observations per bird = 8) and 19 males in saplings (133 total observations; mean number of observations per bird = 7). These males were not singing during observations, and they were not included in the data set of singing males. Data on foraging-site selection in female chaffinches included 23 individuals in mature forest (115 total observations; mean number of observations per female = 5) and 18 individuals in saplings (99 total observations; mean number of observations per female = 5.5). Only one observation was made per bird per day.
To further evaluate the exposure of the singing males, I recorded distance
of the focal bird in relation to the nearest open areas such as forest roads,
edges, meadows, and cuttings, which are often used by hunting sparrowhawks
(Newton, 1986).
Twelve territories measured in the mature forest had an average size of 5100 ± 300 m2 (mean ± SE), whereas 11 territories in the saplings had an average size of 7800 ± 580 m2, and the size difference was significant (two-tailed t test, t = 2.45, df = 10, p <.05). The decreased volume of the canopy in the saplings offers a less profitable feeding substrate, and so the size of territory might reflect the habitat quality. I made observations during calm weather.
Vigilance
To obtain a measure of vigilance, I recorded the behavior of an individual
bird every 30 s. I considered a bird to be vigilant when it was singing or
looking around with its bill parallel with or pointed above the horizontal
plane. The bird was not considered to be vigilant when feeding and preening. I
correlated the average vigilance per individual chaffinch with the average
height per bird per day.
Hawk experiments
To study the influence of sparrowhawks on the selection of singing perch, I
used a cardboard model, painted like a sparrowhawk and released by catapult.
The experiment was carried out in mature forest only. The model glided with a
speed of about 7 m/s, which is comparable to the speed of a sparrowhawk
attacking its prey (Newton,
1986). After the model was released, I recorded the perch adopted
and the rate of singing as soon as the bird began to sing after the
"attack." The experiments were carried out both with individuals
that sang in the lower canopy, to see if they would select a higher singing
perch, and with those that sang in the middle parts of the canopy, to see if
they would select a lower or higher perch or remain at the same height.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
|---|
There were no significant differences in song rates of males singing in the mature forest (mean ± SE = 6.23 ± 0.25 songs/min; range = 1-11) and those in the saplings (mean ± SE = 6.51 ± 0.18 songs/min; range = 2-11; two-tailed t test, t = 1.82, df = 138, p >.05) during the study. However, singing birds selected different canopy heights in the two habitats (Table 1, Figure 1). In mature pines the majority of male chaffinches perched in the lowest canopy or just below the living branches, whereas they usually occupied higher canopy positions in the sapling area (Table 1, Figure 1). Singing activity was different within the canopy: the singing rate of the chaffinches significantly increased toward the lowest canopy and in the tree parts below the mature pine canopy (Figure 2). In contrast, birds sang more frequently in the uppermost canopy parts of smaller saplings (Figure 2). Singing rate also significantly increased from the trunk to the outer part of the canopy in the sapling area (Figure 3). This effect was not observed in mature forest (Figure 3), probably because dead branches below the canopy are usually considerably shorter than living branches in the canopy of mature pine.
|
|
|
|
In mature pines, foraging male chaffinches were observed significantly higher in the tree than singing individuals (two-tailed Mann-Whitney U test, z = 5.88, n1 = 27, n2 = 70, p <.05; Table 1), whereas, in saplings, foraging males were observed significantly lower in the tree than singing individuals (two-tailed Mann-Whitney U test, z = 3.19, n1 = 19, n2 = 70, p <.01). The females foraged higher than the males in young pine canopy (two-tailed Mann-Whitney U test, z = 2.79, n1 = 18, n2 = 19, p <.05). Chaffinch females foraged significantly higher than the singing males in mature pines (two-tailed Mann-Whitney U test, z = 2.21, n1 = 23, n2 = 70, p <.05, Table 1), but significantly lower than the foraging males (two-tailed Mann-Whitney U test, z = 2.79, n1 = 23, n2 = 27, p <.05). The foraging males occupied similar parts of the canopy in both habitats, whereas the foraging height of female chaffinches differed between the habitats (Table 1).
Vigilance
In mature forest, the singing males increased their antipredatory vigilance
when in the lower canopy, and maximum rates of vigilance, expressed as mean
proportions of being vigilant, were recorded below the canopy
(Figure 4). A significant
difference was found between vigilance of males perching below the canopy
(relative heights from — 1.00 to 0.00; mean ± SE time spent
vigilant = 0.98 ± 0.01) and vigilance of males that sang within the
mature pine canopy (relative heights from 0.01 to 1.00; two-tailed
Mann-Whitney U test, n1 = 48,
n2 = 22, z = 6.41, p <.01). In
saplings, vigilance of singing males clearly increased toward the higher
perches (Figure 4).
|
Hawk experiments
The hawk model was usually released within 5-8 m of the focal bird. The
most common escape tactics was a flight upward at a steep angle to the
protective cover of the denser, inner part of the mature pine canopy. However,
the escaping birds did not hide in the middle of the canopy and usually
perched in the lower part (mean ± SE relative height = 0.27 ±
0.03, n = 62). Some of the chaffinches (n = 23) then moved
to lower parts of the canopies of neighboring pines. After the attacks, the
males usually remained motionless for several minutes (5.13 ± 0.67).
All of the experimental males resumed singing within 5-12 min (7.26 ±
0.78) after the attacks, and all of them did so perching below the canopy of
mature pines. The chaffinches that sang within the canopy before the
experimental attacks (mean relative height = 0.28 ± 0.06) significantly
decreased the perch height (mean relative height = -0.06, ± 0.03) to
resume singing after these experiments (two-tailed Wilcoxon matched-pairs
test, n1 = n2 = 32, T = 0,
p <.001). In contrast, the birds that perched in the lower canopy
before the experiments (mean relative height = -0.18 ± 0.03) usually
resumed singing at the same heights (mean relative height = -0.13 ±
0.02) after the experiments were done (two-tailed Wilcoxon matched-pairs test,
n1 = n2 = 30, T = 120,
p >.05). The singing height of chaffinches of both groups did not
differ significantly after the experiments (two-tailed Mann-Whitney U
test, n1 = 32, n2 = 30, z =
2.32, p >.05).
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
|---|
To attract females and repel rivals from territories, male chaffinches utter frequent and loud songs (Marler, 1956
; Slater,
1981). However, those aspects of male vocal behavior that are most
attractive to females such as calling more intensively and producing
frequency-modulated calls are also the ones that most increase predation risk
(I. Krams, unpublished data; Ryan et al.,
1982). Although I did not find any direct evidence that there was
increased risk of being preyed upon, the selection of a singing perch may be
considered an antipredatory response of chaffinches to airborne predators.
Sparrowhawks usually attack small forest birds either below the canopy or
above the canopy, and hence the choice made by male chaffinches may be
considered the most dangerous. Usually there is a trade-off between
reproductive behavior and the risk of predation, provided that the latter is
an important selective force. Predation by sparrowhawks is an important agent
shaping behavior and niche use in forest birds
(Alatalo et al., 1986;
Forsman et al., 1998).
Therefore, one may ask how it is possible to avoid the risk of being preyed
upon by sparrowhawks while at the same time increasing singing rates when
perched in the most risky part of the tree. The first possibility for the
singing individual to avoid predation is to conceal itself in the dense parts
of the canopy. However, this behavior was not observed in the present study.
The second alternative is to sing on an open perch, remaining visible to other
birds including rivals and natural enemies. My results show that the majority
of males preferred to sing below the canopy of mature pines and higher than
their foraging sites in sapling areas, which are the canopy heights where
sparrowhawks hunt most often (Krams,
1996). Still, the males preferred the outer parts of the canopy,
which are not generally considered safe. In winter these parts of the canopy
are usually avoided by dominant members of tit flocks, who perceive foraging
there as a risky (Kullberg,
1998; Suhonen,
1993a,b).
However, chaffinches probably rely on personal vigilance only, whereas the
wintering tits benefit more from collective vigilance
(Ekman, 1987).
Trade-offs related to levels of activity in prey animals are of great
relevance to the ecology of predator—prey interactions. Animals almost
always increase use of refuges or decrease movements outside refuges when risk
of predation is high (Lima and Dill,
1990; Sih, 1987).
However, my results may indicate that in territory advertising, staying in
open sites could be a beneficial strategy for chaffinches because it makes it
possible to improve antipredatory vigilance. The strongest support for this
assumption comes from the hawk experiments. After being exposed to the
sparrowhawk model, all of the singing birds selected the conspicuous perch
below the canopy of mature pines. The males that perched higher in the canopy
before the experiment moved to the lower canopy, whereas those males that sang
below the canopy did not change their singing perch.
The observed behavior of chaffinches at one extreme may be explained by the
"predator selectivity effect," in which predators selectively
attack the less vigilant individuals
(Packer and Abrams, 1990). At
the other extreme, the selection of the perch could be explained by the
"detection effect," in which vigilant birds usually react faster
and escape predators by flying to cover
(Cresswell, 1994;
Lima, 1994). When an attack is
in progress, a singing chaffinch is under less risk if the attack is detected
at its start, not in the final phase. Early detection from a conspicuous perch
such as the lowermost canopy in mature forest and the uppermost canopy in
saplings enables the detector to hide by flying to cover. Sparrowhawks would
not then be able to implement their most successful hunting tactics based on
surprise because the vigilant males would not be surprised. This assumption is
also supported by the higher mortality of female chaffinches found during this
study (13 killed females, presumably by airborne predators, vs. 1 male).
Females foraged higher in the canopy of young pines and lower in mature forest
and so probably lacked the ability to see the surroundings and to hide as well
as the males foraging in denser parts of the canopy. These results differ from
those of Götmark and Post
(1996), who found the singing
perches of males to be higher than their foraging sites. The difference may be
caused by the absence of the understory vegetation in my study area so that
the canopy was the only foraging substrate available to the birds.
Nevertheless, Götmark and Post
(1996) suggested a trade-off
between reproductive success and danger from predation in males and a greater
mortality of females despite their duller plumage.
Perching in the most open parts of the tree can increase both safety and
the individual singing rate. Transmission of long-range sounds increases with
the height of perch (Catchpole and Slater,
1995). However, chaffinches preferred to sing as low as possible
in mature forests, gaining the possibility of seeing the surroundings, in
spite of not being able to avoid the sound attenuation
(Marten and Marler, 1977).
Still, chaffinches use frequencies that carry far so that their loud,
frequency-modulated, long-range songs
(Snow and Perrins, 1997) could
be given from inner or outer parts of the canopy with little difference in
attenuation (Wiley and Richards,
1982). Many studies on the evolution of coloration in birds
suggest that the conspicuous plumages of male birds evolve mainly through
female choice of bright males (Andersson,
1994; Darwin,
1871), and Hingston
(1933) has emphasized the
importance of contest competition between males. Therefore, it may be
advantageous to sing from a more exposed perch where male chaffinches could
see rivals and females and vice versa. However, territory inspection also can
be done well without singing while sitting motionless. Moreover, singing from
an open perch is not necessarily the best way to detect the approaching
rivals. Although brighter plumage (Huhta
et al., 1998;
Rytkönen et
al., 1998) and loud songs make male chaffinches more conspicuous,
the selection of a conspicuous singing perch can compensate for the increased
costs associated with territory advertisement through the enhanced vigilance
that it gives (Lima and Bednekoff,
1999).
|
ACKNOWLEDGEMENTS |
|---|
I am grateful to Peter J. B. Slater and two anonymous referees for valuable comments and suggestions. This study could not have been accomplished without the help of Tatjana Krams, Walther Thiede, and Ilva Everte. I also thank Robert B. Payne for his help with color rings. The work was supported in part by the Science Council of Latvia.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
|---|
Alatalo RV, Gustafsson L, Lundberg A, 1986. Interspecific competition and niche changes in tits (Parus spp.): evaluation of nonexperimental data. Am Nat 127: 819-834.[Web of Science]
Andersson M, 1994. Sexual selection. Princeton, New Jersey: Princeton University Press.
Catchpole CK, Slater PJB, 1995. Bird song: biological themes and variations. Cambridge: Cambridge University Press.
Cresswell W, 1994. Song as a pursuit-deterrent signal, and its occurrence relative to other anti-predation behaviours of skylark (Alauda arvensis) on attack by merlin (Falco columbarius). Behav Ecol Sociobiol 34: 217-223.[Web of Science]
Darwin C, 1871. The descent of man and selection in relation to sex. London: Murray.
Ekman J, 1986. Tree use and predator vulnerability of wintering passerines. Ornis Scand 17: 261-267.
Ekman J, 1987. Exposure and time use in willow tit flocks: the cost of subordination. Anim Behav 34: 445-452.
Forsman JT, Mönkkönen M, Inkeröinen J, Reunanen P, 1998. Aggregate dispersion of birds after encountering a predator: experimental evidence. J Avian Biol 29: 44-48.
Götmark F, Blomqvist D, Johansson OC, Bergkvist J, 1995. Nest site selection: a trade-off between concealment and view of the surroundings? J Avian Biol 26: 305-312.
Götmark F, Post P, 1996. Prey selection by sparrowhawk, Accipiter nisus: relative predation risk for breeding passerine birds in relation to their size, ecology and behaviour. Phil Trans R Soc Lond B 351: 1559-1577.
Haskell D, 1994. Experimental evidence that nestling
begging behaviour incurs a cost due to nest predation. Proc R Soc Lond
B 257:
161-164.
Hingston RWG, 1933. The meaning of animal colour and adornment. London: Edward Arnold.
Huhta E, Hakkarainen H, Lundvall P, 1998. Bright colours and predation risk of passerines. Ornis Fenn 75: 89-93.
Krams IA, 1996. Predation risk and shifts of foraging sites in mixed willow and crested tit flocks. J Avian Biol 27: 153-156.
Krams I, 1998. Dominance-specific vigilance in the great tit. J Avian Biol 29: 55-60.
Kullberg C, 1998. Spatial niche dynamics under predation risk in the willow tit Parus montanus. J Avian Biol 29: 235-240.
Leech SM, Leonard ML, 1997. Begging and the risk of
predation in nestling birds. Behav Ecol
8: 644-646.
Lima SL, 1994. On the personal benefits of anti-predatory vigilance. Anim Behav 48: 734-736.[Web of Science]
Lima SL, Bednekoff PA, 1999. Back to the basic of antipredatory vigilance: can nonvigilant animals detect attack? Anim Behav 58: 537-543.[Web of Science][Medline]
Lima SL, Dill LM, 1990. Behavioral decisions made under the risk of predation: a review and prospectus. Can J Zool 68: 619-640.[Web of Science]
Marler P, 1956. Behaviour of the chaffinch (Fringilla coelebs). Behaviour (suppl.) 5: 1-184.
Marten K, Marler P, 1977. Sound transmission and its significance for animal vocalization. Behav Ecol Sociobiol 2: 271-290.[Web of Science]
Newton I, 1986. The sparrowhawk. Calton, UK: Poyser.
Packer C, Abrams P, 1990. Should co-operative groups be more vigilant than selfish groups? J Theor Biol 142: 341-357.
Redondo T, Castro F, 1992. The increase in risk of predation with begging activity in broods of magpies Pica pica. Ibis 134: 180-187.[Web of Science]
Ryan MJ, Tuttle MD, Rand AS, 1982. Bat predation and sexual advertisement in a neotropical anuran. Am Nat 119: 136-139.[Web of Science]
Rytkönen S, Kuokkanen P, Hukkanen M, Huhtala K, 1998. Prey selection by sparrowhawks Accipiter nisus and characteristics of vulnerable prey. Ornis Fenn 75: 77-87.
Sih A, 1987. Predators and prey lifestyles: an evolutionary and ecological overview. In: Predation; direct and indirect impacts on aquatic communities (Kerfoot WC, Sih A, eds). Hanover, New Hampshire: University Press of New England; 203-224.
Slater PJB, 1981. Chaffinch song repertoires: observations, experiments and a discussion of their significance. Z Tierpsychol 56: 1-24.
Snow D, Perrins C, 1997. The birds of the Western Palearctic. Oxford University Press.
Suhonen J, 1993a. Predation risk influences the use of foraging sites by tits. Ecology 74: 1197-1203.[Web of Science]
Suhonen J, 1993b. Risk of predation and foraging sites of individuals in mixed-species tit flocks. Anim Behav 45: 1193-1198.
Wiley RH, Richards DG, 1982. Adaptations for acoustic communication in birds: sound transmission and signal detection. In: Acoustic communication in birds, vol. 1 (Kroodsma DE, Miller EH, Quellet H, eds). New York: Academic Press; 132-181.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  A. Cockburn, A. H. Dalziell, C. J. Blackmore, M. C. Double, H. Kokko, H. L. Osmond, N. R. Beck, M. L. Head, and K. Wells Superb fairy-wren males aggregate into hidden leks to solicit extragroup fertilizations before dawn Behav. Ecol., May 1, 2009; 20(3): 501 - 510. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Ward, H. M. Lampe, and P. J. B. Slater Singing is not energetically demanding for pied flycatchers, Ficedula hypoleuca Behav. Ecol., May 1, 2004; 15(3): 477 - 484. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||