Behavioral Ecology Vol. 12 No. 2: 150-156
© 2001 International Society for Behavioral Ecology
Predator versus prey: on aerial hunting and escape strategies in birds
Department of Animal Ecology, Lund University, Ecology Building, SE-223 62 Lund, Sweden
Address correspondence to A. Hedenström. E-mail: anders.hedenstrom{at}zooekol.lu.se .
Received 15 March 2000; revised 14 June 2000; accepted 16 June 2000.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSDISCUSSIONREFERENCES |
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Predator and prey attack-escape performance is likely to be the outcome of an evolutionary arms race. Predatory birds are typically larger than their prey, suggesting different flight performances. We analyze three idealized attack-escape situations between predatory and prey birds: climbing flight escape, horizontal speeding, and turning and escape by diving. Generally a smaller bird will outclimb a larger predator and hence outclimbing should be a common escape strategy. However, some predators such as the Eleonora's falcon (Falco elenorae) has a very high rate of climb for its size. Prey species with an equal or higher capacity to climb fast, such as the swift Apus apus, usually adopt climbing escape when attacked by Eleonora's falcons. To analyze the outcome of the turning gambit between predator and prey we use a Howland diagram, where the relative linear top speeds and minimum turning radii of prey and predator define the escape and danger zones. Applied to the Eleonora's falcon and some potential prey species, this analysis indicates that the falcon usually wins against the example prey species; that is, the prey will be captured. Level maneuvering hunting is the most common strategy seen in Eleonora's falcons. To avoid capture via use of this strategy by a predator, the prey should be able to initiate tight turns at high linear speed, which is facilitated by a low wing loading (weight per unit of wing area). High diving speed is favored by large size. If close enough to safe cover, a prey might still opt for a vertical dive to escape in spite of lower terminal diving speed than that of the predator. On the basis of aerodynamic considerations we discuss escape flight strategies in birds in relation to morphological adaptations.
Key words: climbing flight, diving, Falco eleonorae, flight performance, Howland diagram, predation, turning gambit.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSDISCUSSIONREFERENCES |
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Depending on size and morphology predatory birds use one or other preferred hunting technique, such as surprise attacks by the sparrowhawk (Accipiter nisus) or the legendary stoop by the perergine (Falco peregrinus) (Cresswell, 1996
; Rudebeck,
1950-1951). Much recent work has focused on fat load management
under perceived or experienced predation risk
(Gosler et al., 1995;
Lilliendahl, 1997;
van der Veen, 1999). Another
line of research has studied escape responses in relation to body mass of
caged birds when attacked by a simulated predator (e. g.,
Kullberg et al., 1996;
Lee et al., 1996;
Lind et al., 1999;
Veasey et al., 1998;
Witter et al., 1994). However,
it remains unclear if the responses observed in such experiments, usually a
reduced take-off angle and speed with increasing body mass, represent the
effect of a chosen strategy or a constraint on flight performance. This
article is not, however, concerned with such take-off escape responses when a
bird is attacked by a predator, but rather with the relative flight
performance between a predator and its prey when both are already airborne.
Lima (1993) reviewed the
literature on escape flight strategies in North American birds when attacked
by a predator.
Size, morphology, and hunting strategy have probably coevolved among
predatory species to maximize success in hunting their most common prey. Prey
species, on the other hand, should evolve adaptations that maximize the
chances of escaping a predator attack, leading to a co-evolutionary arms race
between predator and prey (Dawkins,
1982). In birds, the predator is typically larger than the prey,
and because size has profound effects on aerodynamic performance, we could
expect that the size difference is exploited by the prey when selecting the
best escape strategy. In this article we will consider the interaction between
avian predator and prey involved in attack-escape interactions in open air
space. When attacked by a predator the prey bird only has one goal—to
survive by reaching a safe site before being seized by the predator. In aerial
combat the available strategy set for the prey consists mainly of three
alternatives: (1) escape by outclimbing the predator
(Cade, 1960), (2) escape by
outmaneuvering the predator in a turning gambit
(Howland, 1974), and (3)
escape by diving away from the predator. From the prey's point of view the
choice of the optimal escape behavior will be context dependent. Factors
likely to influence the choice of escape strategy are predator (species, sex,
size), the relative position between prey and predator, speed vectors of prey
and predator when the prey discovers the predator and the state of the prey
(e.g., fuel load, muscle size, condition, etc.). A general model combining all
these factors is unlikely to generate any clear insights. We will focus on the
aerodynamic properties of birds during aerial attacks by considering the three
main escape options by simple scaling analysis of flight performance. To
improve realism and illustrate the general principles we will calculate some
relevant performance measures based on measured flight performance in the
Eleonora's falcon (Falco eleonorae)
(Hedenström
et al., 1999), which preys on migratory birds in the Mediterranean
region during their autumn migration
(Rosén et
al., 1999; Walter,
1979). For comparison we selected some candidate prey species for
which the relevant measures of flight performance were available
(Hedenström and Alerstam,
1992,
1994). Even though our
discussion will focus on the Eleonora's falcon and its prey, our results are
generally applicable to any aerial predator-prey interaction system where the
relative locomotory performances of the predator and prey can be assessed
using either biomechanical principles or experiments.
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METHODS |
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TOPABSTRACTINTRODUCTIONMETHODSDISCUSSIONREFERENCES |
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Information on flight performance in the Eleonora's falcon and seven potential prey species refers to published information of sustained climbing flight (Hedenström and Alerstam, 1992
,
1994;
Hedenström
et al., 1999). Climbing flight performance was measured by using
tracking radar or an optical range finder. Track data were reduced in relation
to wind measurements obtained by tracking ascending helium filled weather
balloons. Sustained climbing flight was taken during at least 240 s to
represent the climb rate that a bird can maintain by aerobic muscle work,
which in principle is for as long as the fuel supply lasts. However, during
very long climbs to high altitudes the climb rate will decline because the air
density declines with increasing altitude
(Pennycuick, 1978). We will
assume that the birds exhibit their maximum power during these climbs or a
constant proportion thereof (cf.
Hedenström
and Alerstam, 1992). Then we can estimate the maximum power
(Pmax) as the sum of the aerodynamic power and the rate of
work required to raise the body against gravity at speed
Vz as:
 | (1) |
) with air density 1.23
kg/m3 representing sea level and standard atmospheric conditions,
but differing by using a value of 0.1 for the body drag coefficient
(Pennycuick et al., 1996). The
estimated Pmax from the measured climbing flights was
taken as the maximum available power from the flight muscles. Maximum
horizontal airspeed (Vmax) was calculated by finding the
speed where the power required for horizontal flight equals
Pmax. This estimate of Vmax relies on
current flight mechanical theory
(Pennycuick, 1989), and
possible future revision of this theory or parameters used may change the
estimates. However, changes to the theory will affect the estimates
approximately equally and presumably the relative difference between the
species will remain largely unaffected. Hence, the general conclusions will
not be subject to features of the aerodynamic theory used.
In a steady horizontal turn a component of the lift force (L) has
to be directed upwards to balance the weight, which determines the maximum
bank angle by cos
= mg/L. The remaining lift can be directed
towards the center of rotation giving a minimum turning radius at a given
angle of bank as:
 | (2) |
is the bank angle
(e.g., Thomas, 1996). For
calculations we will assume the maximum possible bank angle and a maximum lift
coefficient CL = 0.5 at the maximum speed. At low speeds
birds can usually develop a maximum lift coefficient around 1.6, but at high
speeds lift coefficients are in the range 0.3-0.5 (cf.
Pennycuick, 1968).
Morphological data (body mass, wing span and wing area) were taken from the
original sources of flight performance
(Table 1). Measurements refer
to the standard methods used for aerodynamic calculations according to
Pennycuick (1989), hence the
wing area includes the area of the body between the wings. The prey species
used as examples are not necessarily typical prey of the Eleonora's falcon
(cf. Walter, 1979), but they
were chosen because measures of flight performance were available for these
species. However, they do represent similar sizes of typical prey that should
have similar performance measures, and they or close relatives have all been
found among prey in breeding cliffs of Eleonora's falcon
(Spina et al., 1987;
Walter, 1979).
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Escape by climbing flight
If two birds, predator and prey, are on the same level when the prey
discovers the predator, then a good strategy should be vertical escape
upwards, that is, by climbing flight, if the prey possesses a capacity to
climb at a faster rate than the predator. Pennycuick
(1978) derived a formula for
the climbing capacity in birds as:
 | (3) |
is air density and
b is wing span. We can use this formula to calculate how climb rate
scales with body mass by substituting the body mass dependent parameters with
their respective scaling relationship. Greenewalt
(1962) found that flight
muscle mass is relatively independent of body size at 17%, that is,
mm = 0.17m. In isometrically scaled birds maximum
wingbeat frequency scales as f
m-1/3
(Pennycuick, 1975) and wing
span scales as bm1/3. By substituting
these realtions into Equation 2 we get:
 | (4) |
,
1996), and so there is a
trade-off between the two traits. However, wing span (b) is raised to
3/2 and wingbeat frequency is raised to one in Equation 3, and therefore we
might still expect rather long and high aspect ratio wings in birds adapted
for high climbing performance. Selection pressure on size and morphology
should be in the same direction for a predator where climbing flight pursuit
is an important hunting strategy.
Real birds are not isometrically scaled, but wing span tends to increase
faster with increasing body mass (Rayner,
1988), which partly compensates the adverse effects of size on
climb rate. This is particularly obvious in the Eleonora's falcon, which has
an extreme climb rate for its size (Table
2;
Hedenström
et al., 1999). Comparing the prey species with Eleonora's falcon,
it is only the dunlin (Calidris alpina) that surpasses the predator,
and allowing for the variation around the means, possibly also the arctic tern
(Sterna paradisaea) and the swift (Apus apus) would escape
successfully from the falcon by climbing
(Table 2). If the prey species
has a lower climb rate than its predator, then escape climbing is a bad
option, even if starting with an altitude advantage, because the predator will
eventually close the gap in a sustained climb gambit. When attacked by
Eleonora's falcons small passerines such as chaffinch (Fringilla
coelebs) and siskin (Carduelis spinus) should not try climbing
flight escapes (Table 2).
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If a prey is attacked by a predator coming from above, that is, the prey
has a lower initial position than the predator
(Figure 1), it may still be
advantageous to escape by climbing. If we assume that power available from the
flight muscles is independent of forward speed
(Pennycuick, 1968), then the
maximum rate of climb will be associated with the minimum power speed
(Vmp). If power available is speed dependent then maximum
rate of climb will be at a forward speed greater than Vmp
(Thomas and
Hedenström, 1998). The escape should
be directed away from the attacking predator to maximize the flight distance
for the predator (Figure 1). If
the prey reaches the same level as the predator before the predator has closed
the distance, then climbing flight escape is a viable strategy when the
horizontal distance to the predator (D) satisfies the inequality:
 | (5) |
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Escape by horizontal turning gambit
A useful escape tactic to a prey is to initiate a turn before predator
closure and rely on a tight turn radius for escape. The classical example is
the cheetah and gazelle, where the cheetah has the highest top speed but the
gazelle can execute tight turns that are often life-saving maneuvers. Howland
(1974) analyzed the condition
of a two dimensional turning gambit between predator and prey with respect to
maximum linear speed and turn radii. The turning gambit starts with a linear
escape away from the predator, but because the predator has the highest
maximum speed it will close in on the prey. There is, however, a chance to
escape if the prey has a smaller turning radius than the predator and there is
an optimal moment (or distance) to execute the turn
(Howland, 1974). The border
between the danger and safe zones in a Howland diagram is defined by:
 | (6) |
We used available data on flight performance in the Eleonora's falcon and
seven potential prey species representing different size and morphology to
estimate maximum sustained horizontal flight speed and the minimum horizontal
turning radius when initiated at the maximum speed
(Table 2). During circular
horizontal turns at the calculated minimum radii these birds would experience
forces between 2.7g (knot) and 9g (arctic tern), which is of
the same magnitude as the vertical force measured in quail (Coturnix
coturnix) during take-off (Earls,
2000). The falcon has the highest maximum speed and hence would
overtake all the prey species in a straight level escape flight. We have
plotted relative speeds and turning radii for the species in
Table 2 in a Howland diagram
(Figure 2), which indicates
that only one species, the arctic tern, would escape from a turning gambit
with Eleonora's falcon. The other species would be taken by the predator.
However, the three smallest species (swift, chaffinch, and siskin;
Table 2) fall near the border
between the escape and no escape zones
(Figure 2). The points in the
(v,r)-plane of Figure
2 are calculated on the mean performances of the falcon and prey,
but there is individual variation in these and so the border between escape
and no escape should be considered as a band around the curve. Species or
individuals falling close to the curve of
Figure 2 can escape with some
probability, depending on the relative individual flight performances of
predator and prey. Three of the species (knot, dunlin and song thrush) even
have greater turning radii than the predator
(Table 2), and they should
avoid getting involved in a turning gambit with Eleonora's falcons
altogether.
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(Howland, 1974
Escape by diving
Diving or stooping is a typical attack strategy by large falcons, famous by
the performance of the peregrine (Falco peregrinus)
(Alerstam, 1987;
Peter and Kestenholz, 1998;
Tucker, 1998). In a gliding
dive inclined at an angle 
to the horizontal the bird must keep the
wings partly open to provide the lift needed to maintain a constant glide
angle. Using simple fixed wing theory of gliding flight the vertical speed
(Vz) is:
 | (7) |
and Equation 7 becomes:
 | (8) |
 | (9) |
 | (10) |
). A
similar analysis for terminal speed in a vertical dive with completely folded
wings gives the same scaling relationship as Equation 10. Hence, this explains
why large falcons may adopt this attack strategy since they have a speed
advantage with respect to a usually smaller prey bird. However, depending on
the starting positions a prey may escape, and reach a safe site before being
seized, by diving even with a lower terminal speed than the attacking
predator. In a very simple setting, the prey dives to cover with a vertical
dive and the predator attack by an inclined gliding dive from a horizontal
distance D to the prey. Starting at the same level, the prey escapes
if the vertical distance to the ground (h) is:
 | (11) |
Small passerines are often seen trying to escape by vertical dives at high
altitudes over sea, even when Eleonora's falcons are very close to them
(Walter, 1979;
Hedenström and
Rosén, unpublished observations). But often
such escape dives are combined with a sharp pull-up, i.e. initiating of a
loop. This is again an application of the turning gambit. Assuming that the
prey bird reaches its terminal speed velocity in a dive with completely folded
wings, then
 | (12) |
is air density, Sb is body frontal area and
CD,par is the body drag coefficient. If the bird opens its
wings they will create a lift force that can be used to create a centripetal
acceleration in a turn away from the dive path. Initially all that lift is
used to turn, but later along the loop path the same amount of lift also has
to support the weight. The initial turning radius is:
 | (13) |
), we get a similar
outcome as that of the horizontal flight turning gambit (cf.
Figure 2). |
DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSDISCUSSIONREFERENCES |
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Predator and prey interactions often have a great influence on the life of organisms, such as habitat selection, selection of feeding sites, sociality and group living and vigilance (Lima and Dill, 1990
). They can also generate morphological adaptations and
counter adaptations in the predator and prey species to enhance performance of
capturing and escaping, respectively. We have focused our analysis on the
flight performance in birds escaping by one of three main strategies: climbing
away from the predator, outmaneuvering the predator in a horizontal turning
gambit, or diving to safety. The general principles should however be
applicable also to other situations and animals.
In climbing flight escape, performance is enhanced by small size, long
wings, large flight muscles and high wingbeat frequency. When encountering
attacks from Eleonora's falcons, a predator with an exceptional capacity to
climb fast for its relatively large size
(Hedenström
et al., 1999), only the dunlin and possibly also the swift should
escape by climbing (Table 2). In fact, this is the main escape tactic observed in swifts
(Hedenström
et al., 1999; Hedenström A, and
Rosén M, unpublished observations). The dunlin
is usually not a prey of Eleonora's falcons, but when attacked by other
predators climbing escapes have been observed
(Lima, 1993). The wing
morphology of both the swift and the dunlin is characterized by rather high
aspect ratio wings, in line with the prediction for birds adopting climbing
escapes (cf. Table 1). The
skylark (Alauda arvensis) is another species escaping by climbing
(song) flight on attacks by the merlin (Falco columbarius)
(Cresswell, 1994). Skylarks are
known to have capacity for fast climbs
(Hedenström,
1995b). Morphologically the skylark has shorter wings than the
swift and dunlin, but it has larger flight muscles than birds in general
(about 25% of total body mass; Rayner,
1988). Lima (1993)
also reports escape by climbing flight in the short-billed dowitcher
(Limnodromus griseus), American crow (Corvus brachyrhynchos)
and water pipit (Anthus rubescens), and
Hedenström
(1995a) reports an observation
of a flock of white-winged black terns (Chlidonias leucopterus)
escaping by climbing away from a pursuing peregrine. Some large species, such
as the sage grouse (Centrocercus urophasianus), which is a typical
quarry to large falcons, rely on acceleration and high maximum horizontal
speed achieved by large flight muscles and small wings
(Pennycuick et al., 1994). The
maximum speed of the grouse is higher than that of the falcon, but the grouse
would not be able to fly at this speed with aerobic muscle work, and it is
questionable if it can fly at any speed without incurring an oxygen debt
(Pennycuick et al., 1994).
Hence, it needs to find cover soon after having out-speeded a pursuing
falcon.
In the turning gambit a prey will outmaneuver a predator by a combination
of high relative linear top speed and a small turning radius
(Figure 2; Equation 6). Of our
example species only one, the arctic tern, would outperform the Eleonora's
falcon, while two (or possibly three) species were borderline cases
(Figure 2). A small turning
radius is achieved by a low wing loading (large relative wing area) and fast
flight is facilitated by a streamlined body shape, low wing drag (i.e., small
wings), and high power available from the flight muscles (large muscle
fraction). Generally, wing loading increases with increasing body size and so
a small turning radius is obtained by small birds with relatively large, but
short, wings. These features represent a typical passerine, but apparently
also terns are adapted for this sort of gambit by low wing loading and
relatively high top speed (Tables
1 and
2). The Eleonora's falcon
mainly hunts by chasing prey by active maneuvering flight
(Rosén et
al., 1999), perhaps because their main prey (small passerines)
most often try to escape by maneuvering flight. The Howland diagram
(Figure 2) indicates that this
predator should do well by this strategy when compared with some potential
prey species. Field observations show however that success rate is quite low
per attack (11%; Walter,
1979), but once a bird is attacked when passing a colony of
Eleonora's falcons, many falcons will attack in rapid succession resulting in
rather low survival chances for the prey
(Rosén et
al., 1999; Walter,
1979). The survey by Lima
(1993) shows that escape by a
last moment dodge is a very common strategy. Hence, the Howland diagram is a
useful tool for assessing the likely outcome of an attack-escape gambit
between predator and prey in birds. The only condition is that the prey has
the opportunity to first move away from the predator and the ability to
execute turns with minimum radii (Howland,
1974). This generally requires open spaces, such as the aerial
hunting of Eleonora's falcons, which usually takes place at great altitudes
where migrants cruise when passing the Mediterranean sea on autumn migration
(Rosén et
al., 1999). Howland diagrams are also applicable to other
situations, such as birds hawking insects in the air (cf.
Warrick, 1998), bats hunting
moths (Roeder and Treat,
1961), fish hunting in open water
(Arnott et al., 1999) and
cheetah and other terrestrial carnivores hunting on open plains.
Extra lift and still more reduced turning radius may be achieved by
spreading the tail and hence augmenting the lifting surfaces when turning
(Thomas, 1996). Also the prey
can do this, thereby reducing its turning radius by the same amount as the
falcon, provided the relative tail surfaces are the same, in which case the
relative radii will remain unchanged with respect to those calculated in
Table 2. Some species, however,
such as dunlin and knot (Calidris canutus), have relatively small
tails and would not be able to increase lift to the same degree as the falcon,
which has a normal tail size, and consequently do even worse in a turning
gambit than indicated in Figure
2.
In escape by diving the predator has an advantage from its size and will
reach higher maximum terminal speeds than the smaller prey. Birds will
maximize the diving speed by having streamlined bodies and small wings. Many
water birds escape by plunge diving (Lima,
1993), and especially ducks seem to fulfil the requirements for
this. Alerstam (1987), using
tracking radar, reports that his highest measured speed of birds refers to
red-breasted mergansers (Mergus serrator) reaching 43 m/s in a
shallow gliding dive. Passerines also dive when attacked by Eleonora's
falcons, in combination with pull-ups, hence executing a vertical turning
gambit. Small birds should be able to execute relatively tighter turns when
initiated at a very high speed, as during a vertical dive with completely
folded wings, where the larger predator might not be able to achieve its
theoretical minimum turning radius for structural safety reasons (cf.
Howland, 1974). Swifts were
never observed diving when escaping from Eleonora's falcons, perhaps because
their long wings generate too much drag even when folded.
In this article we have focused on how aerodynamic theory may be used to
analyze attack-escape performance in birds by indicating the direction of
selection on morphology for improved flight performance. Our analyses show
that depending on escape strategy, there may be partly diverging selection
pressures on morphology. This, in turn, suggests that a species should be
generally best adapted for escaping by a certain method, that is,
"escape specialists" rather than "escape generalists."
The swift is an example of a species that invariably escape by climbing flight
when attacked by Eleonora's falcons. Lima's
(1993) survey indicated that
many species seem to prefer one main strategy, but several species may select
one of the alternative strategies. However, our analyses also show that the
relative performances of the prey and predator should influence the escape
strategy selected. Also, the relative positions between the predator and prey
birds, such as vertical and horizontal distances, decide the escape strategy
selected. By always maximizing the distance and trajectory to the predator, a
prey will inflict the maximum energy cost to the predator
(Weihs and Webb, 1984), which
eventually can force the predator to abort the attack. In line with the
life-dinner principle (Dawkins,
1982) the predator should consider energy costs associated with
prey capture, while the prey should pay little attention to energy costs per
se
(Hedenström
and Alerstam, 1995). Studying sparrowhawk attacks on birds,
Cresswell (1995) found that the
hawks preferred prey in the size range 101-150 g. This could be due to the
relative maneuverability of this size class in relation to small prey (
50
g) that may escape more easily. It may also be that large prey was preferred
because they are more profitable than small prey. In another study, Cresswell
(1993) found that redshanks
(Tringa totanus) responded differently on attacks by three different
bird predators, supporting our flight mechanics results. Hence, when possible,
the prey should obtain information such as species, distance, speed, and
flight direction about the attacking predator for appropriate choice of escape
response that maximizes the survival chances. When facing surprise attacks
this might not be possible, and the prey bird might rather chose a standard
escape response. This situation could be what cage escape flight experiments
represent (e.g., Lind et al.,
1999; Veasey et al.,
1998; Witter et al.,
1994). However, Kullberg et al.
(1998) found that the escape
trajectory of great tits (Parus major) depended on the attack angle
of a model predator.
It is of course naïve to believe that selection for efficient escape performance is the only factor that matters to shape a bird's morphology. Selection for efficient foraging, migration and display should also be important selective agents. Predation may, however, be such an important selective force that it results in significant features in the prey species' size and morphology. Some typical prey species to the Eleonora's falcon, for example swifts, swallows and flycatchers, are themselves aerial predators, which could involve selection on size and morphology in the same direction as selection for efficient escape from an aerial predator. But depending on the escape response of invertebrate prey, small birds may face conflicting selective demands for their own foraging efficiency and escape flight performance.
Finally, even if the aerodynamic theory used is revised in the future, we
think that the general conclusions will remain valid. Measuring the maximum
flight performance of birds is a challenge (cf.
Chai and Dudley, 1999;
Marden, 1987), but such data
can be used to assess the relative flight performance of predator and prey by
using Howland diagrams. They can also help us understand why birds are
designed as they are. It is extremely difficult to measure the flight
trajectories of two birds during attack-escape maneuvers in the wild. However,
such measurements and high-speed films of these interactions would be most
welcome.
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ACKNOWLEDGEMENTS |
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We thank Fernanda Diana for inviting us to work with the Lega Italiana Protezione Uccelli (LIPU) project as a base and for her support during our stays. We are also grateful to Alberto Badami, Nicola Fara, Franco Fadda, Maurizio Medda, Fernando Spina, and Susanne
kesson for assistance during fieldwork that
inspired our thinking on aerial predation. Erik Svensson and S.
kesson gave much appreciated comments on the
manuscript. This research was supported by the Swedish Natural Science
Research Council (given to A.H.). |
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSDISCUSSIONREFERENCES |
|---|
Alerstam T, 1987. Radar observations of the stoop of the peregrine falcon Falco peregrinus and the goshawk Accipiter gentilis. Ibis 129: 267-273.[Web of Science]
Andersson M, Norberg R,
1981. Evolution of reversed sexual size dimorphism and role
partitioning among predatory birds, with a size scaling of flight performance.
Biol J Linn Soc 15:
105-130.
Arnott SA, Neil DM, Ansell AD, 1999. Escape trajectories of the brown shrimp Crangon crangon, and a theoretical consideration of initial escape angles from predators. J Exp Biol 202: 193-209.[Abstract]
Cade TJ, 1960. Ecology of the peregrine and gyrfalcon populations in Alaska. Berkeley, California: University of California Press.
Chai P, Dudley R, 1999. Maximum flight performance of humming-birds: capacities, constraints, and trade-offs. Am Nat 153: 398-411.[Web of Science]
Cresswell W, 1993. Escape response by redshanks, Tringa totanus, on attack by avian predators. Anim Behav 46: 609-611.
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 merlins (Falco columbarius). Behav Ecol Sociobiol 34: 217-223.[Web of Science]
Cresswell W, 1995. Selection of avian prey by wintering sparrowhawks Accipiter nisus in southern Scotland. Ardea 83: 281-389.[Web of Science]
Cresswell W, 1996. Surprise as a winter hunting strategy in sparrowhawks Accipiter nisus, peregrines Falco peregrinus and merlins F. columbarius. Ibis 138: 684-692.[Web of Science]
Dawkins R, 1982. The extended phenotype. Oxford: Oxford University Press.
Earls KD, 2000. Kinematics and mechanics of ground take-off in the starling Sturnus vulgaris and the quail Coturnix coturnix. J Exp Biol 203: 725-739.[Abstract]
Gosler AG, Greenwood JJD, Perrins C, 1995. Predation risk and the cost of being fat. Nature 377: 621-623.
Greenewalt CH, 1962. Dimensional relationships for flying animals. Smithsonian Misc Coll 144(2): 1-46.
Hedenström A, 1995a. Ecology of avian flight (PhD dissertation). Lund: Lund University.
Hedenström A, 1995b. Song flight performance in the skylark Alauda arvensis. J Avian Biol 26: 337-342.
Hedenström A, Alerstam T,
1992. Climbing performance of migrating birds as a basis for
estimating limits for fuel-carrying capacity and muscle work. J Exp
Biol 164:
19-38.
Hedenström A, Alerstam T, 1994. Optimal climbing flight in migrating birds: predictions and observations of knots and turnstones. Anim Behav 48: 47-54.
Hedenström A, Alerstam T, 1995. Optimal flight speed of birds. Phil Trans R Soc Lond B 348: 471-487.
Hedenström A,
Rosén M,
kesson S, Spina F, 1999. Flight
performance during hunting excursions in Eleonora's falcon Falco
eleonorae. J Exp Biol 202:
2029-2039.[Abstract]
Howland HC, 1974. Optimal strategies for predator avoidance: the relative importance of speed and manoeuvrability. J Theor Biol 47: 333-350.[Web of Science][Medline]
Kullberg C, Fransson T, Jakobsson S, 1996. Impaired
predator evasion in fat blackcaps. Proc R Soc Lond B
263: 1671-1675.
Kullberg C, Jakobsson S, Fransson T, 1998. Predator
induced take-off strategy in great tits (Parus major). Proc R
Soc Lond B 265:
1659-1664.
Lee SJ, Witter MS, Cuthill IC, Goldsmith AR, 1996.
Reduction in escape performance as a cost of reproduction in gravid starlings
Sturnus vulgaris. Proc R Soc Lond B
263: 619-624.
Lilliendahl K, 1997. The effect of predator presence on body mass in captive greenfinches. Anim Behav 53: 75-81.
Lima SL, 1993. Ecological and evolutionary perspectives on escape from predatory attacks: a survey of North American birds. Wilson Bull 105: 1-47.
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]
Lind J, Fransson T, Jakobsson S, Kullberg C, 1999. Reduced take-off ability in robins (Erithacus rubecula) due to migratory fuel load. Behav Ecol Sociobiol 46: 65-70.
Marden JH, 1987. Maximum lift production during
takeoff in flying animals. J Exp Biol
130: 235-258.
Pennycuick CJ, 1968. Power requirements for horizontal
flight in the pigeon Columba livia. J Exp Biol
49: 527-555.
Pennycuick CJ, 1975. Mechanics of flight. In: Avian biology (Farner DS, King JR, eds). New York: Academic Press; 1-75.
Pennycuick CJ, 1978. Fifteen testable predictions about bird flight. Oikos 30: 165-176.[Web of Science]
Pennycuick CJ, 1989. Bird flight performance: a practical calculation manual. Oxford: Oxford University Press.
Pennycuick CJ, 1996. Wingbeat frequency of birds in steady cruising flight: new data and improved predictions. J Exp Biol 199: 1613-1618.[Abstract]
Pennycuick CJ, Fuller MR, Oar JJ, Kirkpatrick SJ, 1994. Falcon versus prey: flight adaptations of a predator and its prey. J Avian Biol 25: 39-49.
Pennycuick CJ, Klaassen M, Kvist A,
Lindström ,
1996. Wingbeat frequency and the body drag anomaly: wind-tunnel
observations on a thrush nightingale (Luscinia luscinia) and a teal
(Anas crecca). J Exp Biol 199:
2757-2765.
Peter D, Kestenholz M, 1998. Sturzflüge von Wanderfalke Falco peregrinus und Wüstenfalke F. pelegrinoides. Orn Beob 95: 107-112.
Rayner JMV, 1988. Form and function in avian flight. Curr Ornithol 5: 1-66.
Roeder KD, Treat AE, 1961. The detection and evasion of bats by moths. Amer Sci 49: 135-148.
Rosén M,
Hedenström A, Badami A, Spina F,
kesson S, 1999. Hunting flight
behaviour of the Eleonora's falcon Falco eleonorae. J Avian
Biol 30:
342-350.
Rudebeck G, 1950-1951. The choice of prey and modes of hunting of predatory birds with special reference to their selective effect. Oikos 2: 65-88, 3:200-231.
Spina F, Scappi A, Berthemy B, Pinna G, 1987. The diet of Eleonora's falcon Falco eleonorae in a colony of the western coast of Sardinia with some remarks on the migration of small passerines through the Mediterranean. Suppl Ric Biol Selvaggina 12: 235-254.
Thomas ALR, 1996. The flight of birds that have wings and tail: variable geometry expands the envelope of flight performance. J Theor Biol 183: 237-245.
Thomas ALR, Hedenström A, 1998. The optimum flight speeds of flying animals. J Avian Biol 29: 469-477.
Tucker VA, 1998. Gliding flight: speed and
acceleration of ideal falcons during diving and pull out. J Exp
Biol 201:
403-414.
van der Veen IT, 1999. Effects of predation risk on
diurnal mass dynamics and foraging routines of yellowhammers (Emberiza
citrinella). Behav Ecol 10:
545-551.
Veasey JS, Metcalfe N, Houston DC, 1998. A reassessment of the effect of body mass upon flight speed and predation risk in birds. Anim Behav 56: 883-889.[Web of Science][Medline]
Walter H, 1979. Adaptations to prey and habitat in a social raptor. Chicago: University of Chicago Press.
Warrick DR, 1998. The turning-and linear-maneuvering performance of birds: the cost of efficiency for coursing insectivores. Can J Zool 76: 1063-1079.
Weihs D, Webb PW, 1984. Optimal avoidance tactics in predator prey interactions. J Theor Biol 106: 189-206.
Witter MS, Cuthill IC, Bonser RHC, 1994. Experimental investigations of mass-dependent predation risk in the European starling, Sturnus vulgaris. Anim Behav 48: 201-222.
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