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Cited by 13Avian ecology and behaviorAnimal Behavior and ReproductionBiomimetic flight and propulsion mechanisms

Sexual size dimorphism, prey morphology and catch success in relation to flight mechanics in the peregrine falcon: a simulation study

Open access
Mills, Robin, Taylor, Graham K., Hemelrijk, Charlotte K.·2019·Journal of Avian Biology
DOI 10.1111/jav.01979PMC PMC7613156
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Abstract

In common with many other raptors, female peregrine falcons Falco peregrinus are about 50% heavier than males. Their sexual dimorphism is thought to allow breeding pairs to exploit a wider range of prey through a division of labor: the male being able to catch more maneuverable prey species; the female capable of carrying larger ones. Given the difficulty of assessing the catch success and load carrying capacity of both sexes of falcon in the field, we here adopt a novel approach to test the division‐of‐labor theory by using a detailed physics‐based flight simulator of birds. We study attacks by male and female peregrines on prey species ranging from small passerines to large ducks, testing how catch success relates to the flight performance of predator and prey. Males prove to be better than females at catching highly maneuverable prey in level flight, but the catch success of both sexes improves and becomes more similar when diving, because of the higher aerodynamic forces that are available to both sexes for maneuvering in high‐speed flight. The higher maximum roll acceleration of the male peregrine explains its edge over the female in catching maneuverable prey in level flight. Overall, catch success is more strongly influenced by the differences in maneuverability that exist between different species of prey than between the different sexes of falcon. On the other hand, the female can carry up to 50% greater loads than the male. More generally, our detailed simulation approach highlights the importance of several previously overlooked features of attack and escape. In particular, we find that it is not the prey's instantaneous maximum centripetal acceleration but the prey's ability to sustain a high centripetal acceleration for an extended period of time that is the primary driver of the variation in catch success across species.

AI snapshot

Written from the paper’s full text.

TL;DR

Using a physics-based flight simulator, this study tests the division-of-labor hypothesis in peregrine falcons and finds that males are slightly better than females at catching maneuverable prey in level flight, but the difference diminishes in high-speed stoops. Prey flight performance, especially sustained load factor, drives catch success more strongly than falcon sex, while females can carry up to 50% heavier loads.

Key findings

  • Males had slightly higher catch success than females for most prey species, especially in low-altitude attacks; the difference diminished in high-altitude stoops and disappeared for mallards. Catch success was highest against mallards, then common starlings, rock doves, blue tits, common swifts, and lowest against common chaffinches.
  • Catch success was highest from high altitude, intermediate from moderate altitude, and lowest from low altitude. For chaffinches, catch success was 7.5 times higher from high altitude than low altitude; for mallards, the ratio was only 1.2.
  • Prey maximum load factor strongly affected catch success: if prey load factor matched or exceeded the falcon’s, almost no prey were caught. The prey’s mean sustained load factor was the primary driver of interspecific variation in catch success, whereas prey roll acceleration did not greatly affect it.
  • The female falcon was predicted to carry 0.76 kg of prey versus 0.50 kg for the male, up to 50% greater; both sexes could carry all modeled prey except the mallard in sustained level flight. Maximum sustained level speed was 28.1 m s⁻¹ for males and 29.2 m s⁻¹ for females, and female terminal dive speed was 7.1 m s⁻¹ higher.

Methods

  • Three in silico experiments used a physics-based bird flight simulator with six degrees of freedom, blade-element aerodynamics, pure proportional navigation guidance, visual error, and genetic algorithms to optimize prey erratic maneuvers and the falcon’s navigation constant.
  • Experiment 1 simulated male and female falcons attacking six prey species from three initial altitudes (1500 m, 200 m, and 50 m above prey), with 10⁵ simulations per combination. Experiment 2 simulated a male falcon attacking prey with independently varied speed (0–100 m s⁻¹), maximum load factor (0–15), and maximum roll acceleration (0–8000 m s⁻²), using 10⁶ samples and generalized additive models. Experiment 3 simulated a generic raptor attacking a blue tit or mallard with varied speed, load factor, and roll acceleration, also using 10⁶ samples and GAMs.
  • Catch success was defined as an intercept when predator–prey distance was <0.2 m; a near-miss occurred when the predator came within 5 m but then lost the prey in a 90° blind zone. GAMs used a logit link with smooth terms for load factor, roll acceleration, and speed.

Limitations

  • The paper states that the simulation makes simplifying assumptions about mechanics, aerodynamics, response delays, and the visual system, and may not capture all important aspects of attack and escape. It also notes that morphological parameters have varying measurement error and that no quantitative uncertainty bounds are placed on flight-performance estimates, though a sensitivity analysis is cited elsewhere.
  • The paper states that prey do not precisely time their erratic maneuvers, so they might evade more successfully by timing escape maneuvers in response to the predator’s velocity and position.
  • Evident from the text: the study is purely in silico, assumes lone falcons attacking lone prey in open high-altitude space, and does not include environmental variation, motivation, or field validation.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1111/jav.01979

Cites

42 of 42 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

8 of 31 cited sources checked · 4 supported · 1 flagged · accuracy not yet measured

  • Interpretationcitation

    Very high flight speeds are important to falcons because of the higher load factors and higher roll accelerations that they enable, rather than because of the high speed of the motion per se.

    “As we have shown elsewhere (Mills et al. 2018), very high flight speeds are important to falcons because of the higher load factors and higher roll accelerations that they enable, rather than because of the high speed of the motion per se.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Mills et al. 2018 source

      In Results, under “What mechanisms underlie the increased catch success in a stoop?”, the paper says higher load factors and roll accelerations partly explain the benefit of high speed. But it explicitly finds that high flight speed is also beneficial in and of itself, contrary to the claim’s “rather than” distinction. (LLM, conf=0.90)

      Checked by a reasoning model — may be wrong.

      Experimental — accuracy not yet measured
  • Premisecitation

    Peregrine flight trajectories follow a guidance law called pure proportional navigation.

    “It has been shown experimentally that the flight trajectories of peregrines follow a guidance law called pure proportional navigation (Brighton et al. 2017).”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Brighton et al. 2017 source

      The section ‘Peregrine Terminal Attack Trajectories Are Well Modeled by a PN Guidance Law’ reports that proportional navigation simulations reproduce much of the observed turning in peregrine attacks. The ‘Optimization of the Navigation Constant’ section calls the fitted model ‘pure PN,’ but notes that a trajectory generated by augmented PN could appear to follow pure PN when approximated by that model. The experiments therefore support a good fit to pure PN, not a definitive finding that the birds follow that exact law. (LLM, conf=0.82)

      Experimental — accuracy not yet measured
  • Interpretationcitation

    Catch success in our simulations is expected to be the result of a complex interplay between various aspects of flight performance, together with the guidance behavior, response delays and visual error of the peregrine.

    “All things considered, catch success in our simulations is expected to be the result of a complex interplay between these various aspects of flight performance, together with the guidance behavior, response delays and visual error of the peregrine (Mills et al. 2018).”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Mills et al. 2018 source
  • Premisecitation

    Response delays and errors in vision require the attacker to use an appropriately tuned guidance algorithm when intercepting prey.

    “First, as shown by our previous work (Mills et al. 2018), response delays and errors in vision require the attacker to use an appropriately tuned guidance algorithm when intercepting prey.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Mills et al. 2018 source
  • Premisecitation

    Only females have been observed to carry large prey such as mallards.

    “The maximum load that a peregrine can carry has never been tested empirically, but only females have been observed to carry large prey such as mallards (Parker 1979, Dekker 1980, 1987).”
    Quote in the paperSubstantial claim1 of 3 sources checked
    • cites Parker 1979

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites Dekker 1980 source

      The Waterfowl section (page unavailable) says that mallards were rarely taken and only by females. It does not say that females carried mallards, so the claim about carrying them goes beyond the reported observation. (LLM, conf=0.84)

      Experimental — accuracy not yet measured
    • cites Dekker 1987 source
  • Classified as probably not a substantial claim. 15
  • May combine two claims. 43

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Successful interception is only possible given precise vision, quick reactions and a suitably tuned guidance law.

    “As we have shown elsewhere (Mills et al. 2018), successful interception is only possible given precise vision, quick reactions and a suitably tuned guidance law.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites Mills et al. 2018 source

      The Abstract says that high-speed stoops against maneuvering prey require appropriately tuned guidance and precise vision and control. The Results section, “Response delays and errors in vision and control drive the need to stoop” (page unavailable), finds that longer response delays reduce catch success, but also says slower responses can be compensated for by diving from higher altitudes. The claim overstates these simulation findings as conditions for any successful interception. (LLM, conf=0.86)

      Experimental — accuracy not yet measured

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductreasoning

    In the absence of any detailed knowledge of this measurement error, we are unable to place any quantitative uncertainty bounds on the estimates of flight performance in our model.

    “In the absence of any detailed knowledge of this measurement error, we are unable to place any quantitative uncertainty bounds on the estimates of flight performance in our model (but see Mills et al. 2018 for a sensitivity analysis to errors in reaction time, visual error or navigation constant).”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites Mills et al. 2018 source

  • May combine two claims.

    Study design and conductcitation

    Our simulation model incorporates many details of bird flight and matches empirical measurements of their flight performance closely.

    “These and a number of other complexities are captured in detail by our simulation model, which incorporates many details of bird flight and matches empirical measurements of their flight performance closely (Mills et al. 2018).”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Mills et al. 2018 source

  • May combine two claims.

    Findingown data

    All modelled prey species except the mallard have a higher maximum load factor, a higher maximum roll acceleration and a tighter minimum turn radius than the falcon when both are flying at their top sustainable horizontal speeds.

    “all of the modelled prey species except the Mallard have a higher maximum load factor, a higher maximum roll acceleration and a tighter minimum turn radius than the falcon when both are flying at their top sustainable horizontal speeds”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: The bird’s immediate objective is to fly as fast as it can, subject to meeting the acceleration demands of its guidance system as closely as possible.

  • May combine two claims.

    Findingown data

    The ability of the falcon to outpace most prey in level flight is not sufficient to guarantee catch success in a horizontal chase, because all prey species except the mallard can still escape by outmaneuvering the falcon.

    “The ability of the falcon to outpace most of its prey in level flight is not sufficient to guarantee catch success in a horizontal chase, however, because our modelling shows that all of the prey species except the mallard can still escape by outmaneuvering the falcon.”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: The bird’s immediate objective is to fly as fast as it can, subject to meeting the acceleration demands of its guidance system as closely as possible.

  • May combine two claims.

    Findingreasoning

    Catch success of both sexes improves and becomes more similar when diving.

    “the catch success of both sexes improves and becomes more similar when diving”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: The bird’s immediate objective is to fly as fast as it can, subject to meeting the acceleration demands of its guidance system as closely as possible.

  • May combine two claims.

    Findingnone given

    Female peregrine falcons are about 50% heavier than males; male peregrines are on average two-thirds the body mass of females.

    “In common with many other raptors, female peregrine falcons Falco peregrinus are about 50% heavier than males.”
    • Also stated in: § Comparative flight performance of falcons and their prey · plain
      “Male peregrines are on average two-thirds the body mass (mb) of females.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Maximum speed in sustained level flight is 28.1 m s−1 for the male and 29.2 m s−1 for the female.

    “the maximum speed in sustained level flight is 28.1 m s−1 for the male and 29.2 m s−1 for the female (Fig. 3a)”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: The bird’s immediate objective is to fly as fast as it can, subject to meeting the acceleration demands of its guidance system as closely as possible.

  • May combine two claims.

    Findingown data

    The prey's maximum load factor strongly affects the falcon's catch success, both when the falcon attacks horizontally, and when it attacks in a high-altitude stoop.

    “By artificially varying the maximum load factor (lift divided by weight) that the prey can exert, we find that the prey’s maximum load factor strongly affects the falcon’s catch success, both when the falcon attacks horizontally, and when it attacks in a high-altitude stoop (Fig. 5a–b).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Males have particularly higher catch success than females in attacks from low altitude, and the difference in catch success diminishes when both sexes attack from high altitude.

    “Males have particularly higher catch success than females in attacks from low altitude, and the difference in catch success diminishes when both sexes attack from high altitude (Fig. 4c).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    In general, the smaller the prey, the greater the advantage of the male over the female, but the ratio is not monotonically increasing with decreasing prey size.

    “In general, the smaller the prey, the greater the advantage of the male over the female, but the ratio is not monotonically increasing with decreasing prey size (follow triangles of one color from left to right in Fig. 4c).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Male falcons are found to be a small fraction better than females at catching most prey species, except the mallard, which they both catch equally well.

    “Male falcons are found to be a small fraction better than females at catching most prey species, except the mallard, which they both catch equally well (Fig. 4c).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    At their respective top sustainable horizontal flight speeds, the prey always have a higher maximum load factor and roll acceleration than the falcon, whereas the situation is reversed at their respective top dive speeds.

    “at their respective top sustainable horizontal flight speeds (ends of the solid lines in (Fig. 3c–d), the prey always have a higher maximum load factor and roll acceleration than the falcon, whereas the situation is reversed at their respective top dive speeds”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: The bird’s immediate objective is to fly as fast as it can, subject to meeting the acceleration demands of its guidance system as closely as possible.

  • May combine two claims.

    Findingown data

    After the mallard, catch success is next highest against the common starling, followed by the rock dove, blue tit and the common swift.

    “After the mallard, catch success is next highest against the common starling, followed by the rock dove, blue tit and the common swift.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingreasoning

    Catch success for every prey species is highest in a high altitude attack, intermediate in an attack from moderate altitude, and lowest in an attack from low altitude.

    “Catch success for every prey species is highest in a high altitude attack, intermediate in an attack from moderate altitude, and lowest in an attack from low altitude.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    At any given airspeed, the maximum achievable load factor and maximum achievable roll acceleration are both higher for the male.

    “At any given airspeed, the maximum achievable load factor and maximum achievable roll acceleration are both higher for the male (Fig. 3c–d).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    At the point of intercept, a stooping female achieves almost the same load factor and roll acceleration as the male, but only because she can dive faster.

    “At the point of intercept, a stooping female achieves almost the same load factor and roll acceleration as the male (Table 2), but only because she can dive faster (Fig. 3b–d).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Model falcons maximize catch success in a high-speed stoop: by gaining speed, model falcons simultaneously gain a high load factor and a high roll acceleration.

    “These results also confirm why our model falcons maximize catch success in a high-speed stoop: by gaining speed, model falcons simultaneously gain a high load factor (Fig. 3c) and a high roll acceleration (Fig. 3d).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Both sexes are well capable of catching all of the prey species we studied, so there is no exclusion of uncatchable species for the female.

    “because we find that both sexes are well capable of catching all of the prey species we studied, there is no exclusion of uncatchable species for the female.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    There is a marked difference in prey choice between male and female peregrines: males take smaller prey, while females hunt larger birds up to the size of ducks.

    “Interestingly, there is a marked difference in the choice of prey between male and female peregrines (Dekker 2009).”
    • Also stated in: § Introduction · plain
      “Males consistently bring smaller prey back to the nest (Parker 1979) and are more often observed to hunt for small passerines (e.g. common starlings Sturnus vulgaris) and small waders (e.g. dunlins Calidris alpina), whereas females hunt more often for larger birds up to the size of ducks (e.g. northern pintails Anas acuta) (Dekker 1980, 1987, 2009).”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites Dekker 2009 source
    • cites Parker 1979

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites Dekker 1980, 1987, 2009

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Premisecitation

    Parasite drag on the body scales with body frontal area, which in turn scales as Sb∝mb0.68.

    “because the parasite drag on the body scales with body frontal area, which in turn scales as Sb∝mb0.68 (Nudds and Rayner 2006)”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Nudds and Rayner 2006 source

  • May combine two claims.

    Interpretationreasoning

    The aspect ratio of the female's wings is lower than that of the male, so she encounters higher induced drag in both flapping and gliding flight.

    “as the aspect ratio of the female’s wings is lower than that of the male, she encounters a higher induced drag in both flapping and gliding flight.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationcitation

    Both attacker and attacked should aim to maximize forward speed when turning.

    “This implies that both attacker and attacked should aim to maximize forward speed when turning.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Simulations of missile behavior show that miss distance decreases as maximum centripetal acceleration increases, and increases as target acceleration increases.

    “Second, simulations of missile behavior show that their miss distance decreases as their maximum centripetal acceleration increases, and increases as target acceleration increases (Shneydor 1998, Palumbo et al. 2010).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites Shneydor 1998 source
    • cites Palumbo et al. 2010

  • May combine two claims.

    Premisecitation

    The jinking escape pattern has never been studied in birds; previous research has focused on escape by climbing, diving or turning smoothly.

    “Yet this jinking escape pattern has never been studied in birds, and previous research has instead focused on studying escape by climbing, diving or turning smoothly (Hedenström and Rosén 2001).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Hedenström and Rosén 2001 source

  • May combine two claims.

    Study design and conductown data

    In experiment 1, 105 simulations per combination of falcon sex, attack strategy and prey species give widest 95% confidence interval bounds of catch success narrower than 0.1%, guaranteeing that all visually observable differences in the plots are statistically significant.

    “In experiment 1, we perform 105 simulations for each combination of sex of falcon, attack strategy and prey species, such that the widest 95% confidence interval bounds of the catch success are narrower than 0.1%, which guarantees that all visually observable differences in the plots are statistically significant.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Male falcons are more motivated to catch smaller prey than females, which obscures differences in their actual ability to catch prey.

    “Most problematically, it has been observed that male falcons are more motivated to catch smaller prey than females (Dekker 2009), thereby obscuring any differences in their actual ability to catch them.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Dekker 2009 source

  • Probably not a substantial claim: may not pass S4 (based).

    Premisenone given

    The available centripetal acceleration of any bird increases with its airspeed because of the greater aerodynamic forces produced.

    “The available centripetal acceleration of any bird increases with its airspeed on account of the greater aerodynamic forces produced”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning

    Deceleration due to parasite drag is lower for the female at a given airspeed, such that she reaches a higher terminal speed than the male while diving under gravitational acceleration with fully retracted wings.

    “the deceleration due to parasite drag is lower for the female at a given airspeed, such that she reaches a higher terminal speed than the male while diving under gravitational acceleration with fully retracted wings.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationcitation

    The female has a greater wing span and area, giving the flight musculature a larger attachment area and increasing the maximum aerodynamic torque she can hold.

    “However, she also has a greater wing span and area, such that the flight musculature has a larger attachment area on the wings, thereby increasing the maximum aerodynamic torque that she can hold (Tucker 1998, Shyy et al. 2013).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites Tucker 1998 source
    • cites Shyy et al. 2013 source

  • May combine two claims.

    Interpretationreasoning

    These prey species should always be able to outmaneuver a falcon, unless the falcon makes use of the absolutely higher maximum load factor and roll acceleration that it can achieve through the extra speed advantage gained by diving.

    “It follows that these prey species should always be able to outmaneuver a falcon, unless the falcon makes use of the absolutely higher maximum load factor and roll acceleration that it can achieve through the extra speed advantage gained by diving”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationnone given

    Exerting a high load factor increases drag, and the flight speed that a maneuvering bird reaches is therefore lower than its top speed in straight level flight.

    “Other things being equal, a bird’s maximum attainable load factor increases with flight speed, but this is not the whole story, because exerting a high load factor increases drag, and the flight speed that a maneuvering bird reaches is therefore lower than its top speed in straight level flight.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: Other things being equal, a bird’s maximum attainable load factor increases with flight speed.

  • May combine two claims.

    Interpretationreasoning

    Neither an erratically-flying prey species nor a falcon maneuvering in response to its prey will actually attain its top sustainable speed in a level chase.

    “so that neither an erratically-flying prey species nor a falcon maneuvering in response to its prey will actually attain its top sustainable speed in a level chase.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: Any kind of maneuvering involves increased drag relative to non-maneuvering flight at the same speed.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    Even our detailed simulation model makes simplifying assumptions regarding the mechanics, aerodynamics, response delays and visual system of the birds.

    “Nevertheless, even our detailed simulation model makes simplifying assumptions regarding the mechanics, aerodynamics, response delays and visual system of the birds.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning

    Even though having a very high flight speed does not in itself increase catch success, it does enhance catch success in conjunction with the high load factor and roll acceleration that high airspeed enables.

    “Thus even though having a very high flight speed does not in itself increase catch success, it does enhance catch success in conjunction with the high load factor and roll acceleration that high airspeed enables.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Study design and conductnone given

    The morphological parameters that are used to compute flight performance have varying degrees of measurement error associated with them.

    “Additionally, the morphological parameters that are used to compute flight performance have varying degrees of measurement error associated with them.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S2 (checkable), S4 (based).

    Interpretationreasoning

    Any such inaccuracy in our quantitative modelling of flight performance should not affect qualitatively the general mechanisms described in this paper.

    “Nevertheless, any such inaccuracy in our quantitative modelling of flight performance should not affect qualitatively the general mechanisms described in this paper.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning

    A wing of low aspect-ratio may increase the instantaneous capacity of the prey to maneuver, by increasing wing area for a given span, but a low aspect ratio wing also generates more drag, which causes the prey to slow down more when maneuvering, and thereby results in a decreased capacity of the prey to maneuver.

    “for instance, while a wing of low aspect-ratio may increase the instantaneous capacity of the prey to maneuver, by increasing wing area for a given span, a low aspect ratio wing also generates more drag, which causes the prey to slow down more when maneuvering, and thereby results in a decreased capacity of the prey to maneuver.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S4 (based). May combine two claims.

    Interpretationreasoning

    Any such inaccuracies are likely to hold equally for both male and female falcons, and their comparative flight performance should therefore be correctly described.

    “Furthermore, any such inaccuracies are likely to hold equally for both male and female falcons, and their comparative flight performance should therefore be correctly described.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Howland's inequality implies that prey can escape by out-turning a predator if and only if the magnitude of their centripetal acceleration exceeds that of their pursuer, which in turn implies that the load factor of the prey must exceed that of the predator.

    “As we discussed in the Methods section, Howland’s inequality implies that prey can escape by out-turning a predator if and only if the magnitude of their centripetal acceleration exceeds that of their pursuer, which in turn implies that the load factor of the prey must exceed that of the predator.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Howland 1974 source

  • Classified as probably not a substantial claim. May combine two claims.

    Interpretationreasoning

    Applying this reasoning to our own model would lead to the conclusion that the prey in our simulations ought never to be able to out-turn a peregrine falcon that is able to reach a high flight speed by stooping, because the maximum achievable load factor of a peregrine is greater than that of any of the modelled prey.

    “Applying this reasoning to our own model would lead to the conclusion that the prey in our simulations ought never to be able to out-turn a peregrine falcon that is able to reach a high flight speed by stooping, because the maximum achievable load factor of a peregrine is greater than that of any of the modelled prey.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    The downsides of flying fast, such as the need to react quickly and accurately, are still captured by our model, which explains why increasing flight speed ultimately becomes detrimental.

    “The physical relationship between these variables is deliberately broken in experiment 3, but the downsides of flying fast, such as the need to react quickly and accurately, are still captured by our model, which explains why increasing flight speed ultimately becomes detrimental.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationreasoning

    Our simulations may not capture all of the important aspects of attack and escape.

    “Our simulations therefore may not capture all of the important aspects of attack and escape, and revised theory in the future may shed light on new mechanisms that either complement or invalidate those described here.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Interpretationnone given

    Our detailed simulation approach incorporates a number of other important factors that determine success in attack and escape.

    “Our detailed simulation approach incorporates a number of other important factors that determine success in attack and escape.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Interpretationreasoning

    The comparatively large rock dove has a lot of meat on it, and is relatively easy for both sexes to catch and carry, which in conjunction with its cosmopolitan abundance may explain why this is one of the most commonly taken prey species for both sexes of peregrine.

    “For example, the comparatively large rock dove has a lot of meat on it, and is relatively easy for both sexes to catch and carry, which in conjunction with its cosmopolitan abundance may explain why this is one of the most commonly taken prey species for both sexes of peregrine.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Even when falcons are not breeding, they tend to bring most of their prey back to their perch, or even to consume their prey mid-air.

    “Hence, even when falcons are not breeding, they tend to bring most of their prey back to their perch, or even to consume their prey mid-air (Dekker 1988).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Dekker 1988 source

  • May combine two claims.

    Premisecitation

    Over 7 yr, the majority of observed solo hunts were performed by the male (432 hunts by the male versus 140 by the female), and while the male tended to specialise on catching small passerines, all of the gulls that it caught were immediately passed or dropped to the female or fledged juveniles, rather than being carried.

    “Over 7 yr, the majority of observed solo hunts were performed by the male (432 hunts by the male versus 140 by the female), and while the male tended to specialise on catching small passerines, all of the gulls that it caught were immediately passed or dropped to the female or fledged juveniles, rather than being carried.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Dekker and Taylor (2005)

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Interpretationreasoning

    The female is able to make up for this slight disadvantage by flying at a higher flight speed than the male, particularly when stooping, which allows her to increase the aerodynamic forces available for maneuvers.

    “The female is able to make up for this slight disadvantage by flying at a higher flight speed than the male, particularly when stooping, which allows her to increase the aerodynamic forces available for maneuvers.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    Falcons should prefer to hunt heavier prey, as our simulation results indicate that catch success for these species is generally higher, and their nutritional value is presumably higher.

    “Other things being equal, this suggests that falcons should prefer to hunt heavier prey, as our simulation results indicate that catch success for these species is generally higher, and their nutritional value is presumably higher.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationreasoning

    It is likely that prey could increase their success at evading the predator by timing escape maneuvers in response to its velocity and position.

    “Our model assumes that the prey do not precisely time their erratic maneuvers, so it is likely that they could increase their success at evading the predator by timing escape maneuvers in response to its velocity and position.”
    Quote in the paperNot a substantial claim
    • The authors state this as an assumption: Our model assumes that the prey do not precisely time their erratic maneuvers.

  • May combine two claims.

    Interpretationreasoning

    While the female has a higher inertia to overcome when maneuvering, she also has a greater muscle mass, a larger wing area and a lower aspect ratio, and the net effect is that she is only slightly less agile than the male when flying at the same flight speed.

    “While the female has a higher inertia to overcome when maneuvering, she also has a greater muscle mass, a larger wing area and a lower aspect ratio, and the net effect is that she is only slightly less agile than the male when flying at the same flight speed.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationreasoning

    The advantage of the lighter male may be an energetic one.

    “The advantage of the lighter male may be an energetic one.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Interpretationnone given

    Optimal prey choice will depend on the net gain in energy expected from a given species, which is a function of the predator's expected catch success, the nutritional value of the prey, and the energetic cost of chasing and carrying the prey.

    “In general, we can expect that optimal prey choice will depend on the net gain in energy expected from a given species, which is a function of the predator’s expected catch success, the nutritional value of the prey, and the energetic cost of chasing and carrying the prey.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S4 (based).

    Premisenone given

    Erratic flight behavior is widespread among alarmed prey.

    “We have focused here on studying the success of peregrines of both sexes hunting prey that maneuver erratically in mid-air, as this erratic flight behavior is widespread among alarmed prey.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: Erratic flight behavior is widespread among alarmed prey.
54 of 54

  • The authors state this as an assumption.

    The bird’s immediate objective is to fly as fast as it can, subject to meeting the acceleration demands of its guidance system as closely as possible.

    “on the assumption that the bird’s immediate objective is to fly as fast as it can, subject to meeting the acceleration demands of its guidance system as closely as possible”

  • The authors state this as an assumption.

    The angular rate of the line-of-sight between the falcon and its prey is measured with error by the visual system.

    “which is assumed to be measured with error by the visual system”

  • The authors state this as an assumption.

    The aerodynamic forces and moments are generated by flapping or gliding, using variable wing retraction as a control.

    “The aerodynamic forces and moments are assumed to be generated by flapping or gliding, using variable wing retraction as a control”

  • The authors state this as an assumption.

    The bird uses bang–bang control to redirect its aerodynamic force vector as quickly as possible when banking to turn.

    “assuming that the bird uses bang–bang control to redirect its aerodynamic force vector as quickly as possible when banking to turn”

  • The authors state this as an assumption.

    The falcon holds its prey facing forward with its wings retracted, such that the additional drag is just the parasite drag of the prey’s body.

    “assuming that the falcon holds its prey facing forward with its wings retracted, such that the additional drag is just the parasite drag of the prey’s body.”

  • The paper relies on this without support.

    Any kind of maneuvering involves increased drag relative to non-maneuvering flight at the same speed.

    “A further complication is that any kind of maneuvering involves increased drag relative to non-maneuvering flight at the same speed”

  • The paper relies on this without support.

    Other things being equal, a bird’s maximum attainable load factor increases with flight speed.

    “Other things being equal, a bird’s maximum attainable load factor increases with flight speed”

  • The paper relies on this without support.

    Male falcons are about two-thirds the size of females.

    “Male falcons are about two-thirds the size of females”

  • The paper relies on this without support.

    Erratic flight behavior is widespread among alarmed prey.

    “as this erratic flight behavior is widespread among alarmed prey”

  • The authors state this as an assumption.

    Our model assumes that the prey do not precisely time their erratic maneuvers.

    “Our model assumes that the prey do not precisely time their erratic maneuvers”

  • The authors state this as an assumption.

    If catch success is comparable between the sexes, then the lighter male will consume less energy in attacking a specific prey species.

    “If catch success is comparable between the sexes, then it is reasonable to assume that the lighter male will consume less energy in attacking a specific prey species.”

  • The paper relies on this without support.

    The maximum load that a peregrine can carry has never been tested empirically.

    “The maximum load that a peregrine can carry has never been tested empirically”
12 of 12

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Howland's inequality is rewritten incorrectly

    Minor

    With the paper's definitions, the prey-to-predator centripetal-acceleration ratio is a = v2/r. Thus a > 1 requires v2 > r, not v > r; the stated conditions are not equivalent. This affects the paper's account of when prey can escape by out-turning a predator.

1 of 1

Cites

Flagged first, then by citations

2 of the 44 references couldn’t be matched to a known paper.

Research works printed but not linked: 4

  1. Dekker D., 2005, A change in foraging success and cooperative hunting by a breeding pair of peregrine falcons and their fledglings, J. Raptor Res, 39, 394
  2. Ferguson‐Lees J., 2001, Raptors of the world
  3. Parker A., 1979, Peregrines at a welsh coastal eyrie, Br. Birds, 72, 104
  4. Ratcliffe D., 2010, The peregrine falcon

Cited by

Sorted by citations

Related

Authors
Mills, R., Taylor, G. K., & Hemelrijk, C. K.
Affiliations
  • University of Groningen (NL)
  • University of Oxford (GB)
Corresponding author
Mills, Robin
ORCID
Venue
Journal of Avian Biology
Publisher
Wiley
Published
2019-03
Volume
50
Issue
3
ISSN
  • 0908-8857 (ISSN-L)
  • 1600-048X
DOI
10.1111/jav.01979
PMC
PMC7613156
OpenAlex
W2917472986
Semantic Scholar
a8e1c6d358bd63642c95148cce0d9a037e59fae3
Cited by
13
References
44
Citations by year
2026: 1 · 2025: 2 · 2024: 4 · 2022: 2 · 2021: 1 · 2020: 2 · 2019: 1
FWCI
0.91
Type
journal article
Language
en
Open access
Licence
Locations
  • Journal of Avian Biology (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • PubMed Central (submittedVersion, cc-by)
  • University of Groningen research database (University of Groningen / Centre for Information Technology) (submittedVersion, cc-by)
Funders
  • European Commission (HORIZON2020)
  • Nederlandse Organisatie voor Wetenschappelijk Onderzoek (823.01.017)
Topics
  • Physical Sciences › Environmental Science › Ecology › Avian ecology and behavior
  • Life Sciences › Agricultural and Biological Sciences › Ecology, Evolution, Behavior and Systematics › Animal Behavior and Reproduction
  • Physical Sciences › Engineering › Aerospace Engineering › Biomimetic flight and propulsion mechanisms
Keywords
Falco peregrinus, sexual size dimorphism, division of labor, flight dynamics, predator-prey interactions, diving, level flight, roll acceleration, bearing capacity, raptors

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-09.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-09.

Cited sources are checked by gpt-6-sol.

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

What counts as a claim ›How we measure confidence ›How we check this ›

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