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Cited by 18Animal Behavior and ReproductionAvian ecology and behaviorMorphological variations and asymmetry

Structural complexity of hunting habitat and territoriality increase the reversed sexual size dimorphism in diurnal raptors

Open access
Pérez‐Camacho, Lorenzo, Martínez‐Hesterkamp, Sara, Rebollo, Salvador, García‐Salgado, Gonzalo, Morales‐Castilla, Ignacio·2018·Journal of Avian Biology
DOI 10.1111/jav.01745
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Abstract

Despite numerous efforts and many hypotheses to explain the selective pressures that may have favoured reversed sexual dimorphism (RSD) in raptors – i.e. that the female is larger than the male – some drivers of RSD are still unknown. Here we analyse how much variation in RSD is explained by hunting habitat structure, territoriality or territory size. We do so using data on diurnal raptors from the New World and the Western Palearctic – i.e. Cathartidae, Pandionidae, Accipitridae and Falconidae, the largest bird group showing RSD – taking into account the phylogenetic relationships among species. Our results identify the type of the main prey as a major factor explaining RSD in raptors. We also found RSD to increase with increasing structural complexity in the hunting habitat from open or semi‐open habitats to forest interior. RSD also increased with increasing degree of territoriality of the species (non‐territorial < facultative < territorial). Finally, for territorial species RSD increased with increasing size of nesting territory. A model comprising only three predictor variables (prey type, structural complexity of hunting habitat and territoriality) explained up to 50% of the variation in RSD of European and American diurnal raptor species, and up to 40% of the variation in RSD when only territorial species were considered. Our results highlight the relevance of spatial facets of the niche – e.g. hunting habitat, territoriality and territory size – in exerting selective pressures on the body size of diurnal raptors. These selective pressures, joint with already known trophic factors – e.g. diet – are decisive for the evolution of the RSD, a key trait in the functional ecology of raptors. Our findings open up new perspectives in the study of sexual size divergence in birds.

AI snapshot

Written from the paper’s full text.

TL;DR

This comparative study of New World and Western Palearctic diurnal raptors finds that reversed sexual size dimorphism (RSD) increases with prey agility, structural complexity of the hunting habitat, territoriality, and territory size. In multiple models, prey agility and hunting habitat are significant predictors, whereas territoriality and territory size correlate bivariately but are not significant in multiple regression.

Key findings

  • Across 75 species, RSD positively correlated with prey agility (r = 0.658, corrected p < 0.001), hunting habitat complexity (r = 0.328, corrected p = 0.017), and territoriality (r = 0.400, corrected p = 0.002); among 36 territorial species, RSD correlated with territory size index (r = 0.434, corrected p = 0.011).
  • In OLS/PGLS multiple models, prey agility had the largest standardized coefficients and was significant (e.g., OLS 75 species β = 0.591, p < 0.001; PGLS β = 0.574, p = 0.000), followed by hunting habitat (OLS β = 0.254, p = 0.004; PGLS β = 0.250, p = 0.006); territoriality and territory size were non-significant in multiple models (e.g., OLS 75 species territoriality β = 0.103, p = 0.27; OLS 36 species territory size β = 0.266, p = 0.122).
  • Partial regressions showed that three predictors together explained up to 50% of RSD variation for all species and up to 40% for territorial species; prey agility explained 43.3% (all species) and 29.2% (territorial species), hunting habitat 10.8% and 5.8%, territoriality 16.0%, and territory size 18.8%, with territoriality/territory size overlapping with prey agility (14.1% and 16.7% shared variation).
  • RSD based on body mass was higher and more sensitive to the explanatory variables than RSD based on cubed wing length (F = 9.31, p = 0.003); PGLS indicated phylogenetic signal in residuals (λ > 0.8, δ > 1.0) but did not change the ranking of predictors.

Methods

  • Comparative analysis of New World and Western Palearctic diurnal raptors: 75 species with complete data on all variables and phylogeny, plus a subset of 36 territorial species with territory-size data.
  • RSD index = 100 × [(female mass − male mass) / (0.5 × (female mass + male mass))], also computed with cubed wing length; predictors were prey agility (6-point scale: carrion to birds), hunting habitat (3-point scale: open to closed), territoriality (0 = non-territorial, 1 = facultative, 2 = territorial), and territory size index = mean nearest-neighbour nest distance / log10(mid-range male body mass).
  • Bivariate correlations with phylogenetic correction (Dutilleul’s method, phylogenetic ANOVA), saturated OLS and PGLS models adjusting λ and δ, partial regressions, and Bayesian MCMC GLMM/PGLMM with phylogeny as a random effect; condition numbers were < 5.

Limitations

  • Stated: results are limited to New World and Western Palearctic species, and future studies should test whether they hold for a global set of diurnal raptors; prey agility was scored by taxonomic grouping of main prey, and the authors call for refinement when accurate proportional diet data become available.
  • Stated: the aim was not to build accurate predictive models but to understand relationships, so only a few high-explanatory variables were tested rather than a comprehensive model.
  • Evident from the text: the comparative/correlational design cannot establish causation; territory-size analysis is restricted to 36 territorial species; ordinal/taxonomic proxies and literature-derived mid-range body masses may introduce measurement error.

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

Integrity signals

Registry

Crossref · 10.1111/jav.01745

Cites

114 of 114 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

7 of 45 cited sources checked · 4 supported · 0 flagged · accuracy not yet measured

  • Premisecitation
    § Territoriality and territory size

    Studies for three diurnal raptor species (Northern goshawk and Black kite in Spain and Brown falcon in Australia) have shown that larger females are more likely to be recruited as breeders than smaller ones.

    “Studies for three diurnal raptor species (Northern goshawk and Black kite in Spain and Brown falcon in Australia) have shown that larger females are more likely to be recruited as breeders than smaller ones (McDonald et al. 2005;Sergio et al. 2007; Pérez-”
    Quote in the paperSubstantial claim2 of 2 sources checked
    • cites McDonald et al. 2005 source
    • cites Sergio et al. 2007 source

      The ‘Arrival and individual quality’ section reports that body size was associated with arrival date for female black kites: larger females arrived earlier. The study concerns settlement on breeding territories, but it does not show that larger females were more likely than smaller females to be recruited as breeders. This citation supports the black-kite size association, not the stated recruitment outcome. (LLM, conf=0.84)

      Experimental — accuracy not yet measured
  • Interpretationcitation
    § Territoriality and territory size

    Territoriality can also promote an increase in female size, as evidenced by previous studies and by our results.

    “However, territoriality can also promote an increase in female size, as evidenced by previous studies (McDonald et al. 2005;Sergio et al. 2007;Pérez-Camacho et al. 2015) and by our results.”
    Quote in the paperSubstantial claim2 of 3 sources checked
    • cites McDonald et al. 2005 source
    • cites Sergio et al. 2007 source

      The ‘Arrival and individual quality’ section reports that larger females arrived earlier, and ‘Arrival and territory quality’ links earlier settlement to better territories (page numbers unavailable). This supports an association between female size and access to territories, but does not show that territoriality causes female size to increase. In ‘Territory takeovers,’ winners were larger, but the size differences were not statistically significant. (LLM, conf=0.83)

      Experimental — accuracy not yet measured
    • cites Pérez-Camacho et al. 2015

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

  • Findingown data
    § Results

    OLS partial regressions confirmed that prey agility explained a larger proportion of RSD variation than the other three predictors.

    “OLS partial regressions confirmed that prey agility explained a larger proportion of RSD variation than the other three predictors, which independently, explained proportions of RSD variation according to the ranking of their OLS and PGLS regression coefficients (multiple regression models; Fig. 3).”
    Quote in the paperSubstantial claim
  • Findingown data
    § Results

    Diurnal raptors that hunt more agile prey had higher RSD than raptors that hunt less agile or immobile prey (r = 0.658, corrected-p < 0.001).

    “Analysis of bivariate relationships between RSD and predictors revealed that diurnal raptors that hunt more agile prey had higher RSD than raptors that hunt less agile or immobile prey (r = 0.658, corrected-p < 0.001; Fig. 1a).”
    Quote in the paperSubstantial claim
  • Findingown data
    § Results

    Territoriality and territory size explained a greater total amount of RSD variation than hunting habitat.

    “Interestingly, territoriality and territory size explained a greater total amount of RSD variation than hunting habitat.”
    Quote in the paperNot a substantial claim
  • Classified as probably not a substantial claim. 22
  • May combine two claims. 27

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

    Premisecitation
    § Introduction

    The higher the speed and agility of the main prey of a raptor, the greater its RSD.

    “For example, several works have documented the effect of prey type, as a surrogate for prey agility, on RSD, suggesting that the higher the speed and agility of the main prey of the raptor, the greater its RSD (Hill 1944;Reynolds 1972;Newton 1979;Wheeler and Greenwood 1983;Temeles 1985;Paton et al. 1994).”
    Quote in the paperNot a substantial claim1 of 3 sources checked
    • cites Hill 1944 source
    • cites Reynolds 1972 source
    • cites Newton 1979

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

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

    Premisecitation
    § Territoriality and territory size

    Previous evidence from a few species suggests that raptor RSD may have evolved by sexual selection through competition among males for a territory, or among females for the best males or territories.

    “This finding extends previous evidence, derived from only a few species, that raptor RSD may have evolved by sexual selection through competition among males for a territory (Widén 1984), or among females for the best males or territories (Sergio et al. 2007;McDonald et al. 2005;Pérez-Camacho et al. 2015).”
    Quote in the paperSubstantial claim2 of 3 sources checked
    • cites Widén 1984 source
    • cites Sergio et al. 2007 source

      The Statistical analyses section says females may choose males, territories, or both, and the Results link female body size with arrival date and earlier settlement with territory quality (page numbers unavailable). These passages support the mate-or-territory choice proposed in the cited clause, but they do not establish that sexual selection through those choices caused raptor reverse sexual size dimorphism. (LLM, conf=0.83)

      Experimental — accuracy not yet measured
    • cites McDonald et al. 2005 source

  • May combine two claims.

    Findingown data
    § Results

    Prey agility was associated with the highest standardised regression coefficients, followed by hunting habitat; these coefficients were significant for OLS and PGLS models.

    “Prey agility was associated with the highest standardised regression coefficients, followed by hunting habitat; these coefficients were significant for OLS and PGLS models.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data
    § Results

    The variation explained by territoriality and territory size partially overlapped with the variation in RSD explained by prey agility, which was 14.1% for the complete set of 75 species and 16.7% for the subset of 36 territorial species.

    “However, the variation explained by these two territorial predictors partially overlapped with the variation in RSD explained by prey agility, which was 14.1% for the complete set of 75 species and 16.7% for the subset of 36 territorial species (Fig. 3 and Supplementary material Appendix 3, Table A1).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data
    § Results

    Territoriality and territory size showed the smallest coefficients, which in no case achieved statistical significance in a multiple linear modelling framework.

    “Territoriality and territory size showed the smallest coefficients, which in no case achieved statistical significance in a multiple linear modelling framework.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data
    § Results

    Species that are territorial during the breeding season showed the greatest RSD, followed by facultative species, and finally by non-territorial species, which showed the smallest RSD (r = 0.400, corrected-p = 0.002).

    “Species that are territorial during the breeding season showed the greatest RSD, followed by facultative species, and finally by non-territorial species, which showed the smallest RSD (r = 0.400, corrected-p = 0.002; Fig. 1c).”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Findingown data
    § Data collection

    The territory size index takes into account the relationship between territory size and species body mass among the species studied, with r = 0.611, p < 0.001.

    “This index takes into account the relationship between territory size and species body mass among the species studied here (data not shown; r = 0.611, p < 0.001; Schoener 1968;Newton 1979;Palmqvist et al. 1996).”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites Schoener 1968 source
    • cites Newton 1979

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

    • cites Palmqvist et al. 1996

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

  • May combine two claims.

    Findingown data
    § Results

    For both species sets, λ was greater than 0.8 and δ was greater than 1.0.

    “To fit the PGLS models, we performed maximum likelihood-based adjustment of the evolutionary parameters λ and δ; for both species sets, λ was greater than 0.8 and δ was greater than 1.0.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data
    § Relative importance of ecological factors

    Three predictor variables together explain up to 50% of the variation in RSD across the entire set of New World and Western Palearctic diurnal raptor species; up to 40% of RSD variation when only territorial species are considered.

    “No more thanOnly three predictor variables together explain up to 50% of the variation in RSD across the entire set of New World and Western Palearctic diurnal raptor species; up to 40% of RSD variation when only territorial species are considered.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data
    § Territoriality and territory size

    Statistical significance as measured by a phylogenetic ANOVA was found for agility of the main prey (F= 11.564; p = 0.001), hunting habitat (F= 7.987; p = 0.038) and nesting territoriality (F= 7.239; p = 0.015).

    “Statistical significance as measured by a phylogenetic ANOVA (Garland et al. 1993) was found for agility of the main prey (F= 11.564; p = 0.001), hunting habitat (F= 7.987; p = 0.038) and, nesting territoriality (F= 7.239; p = 0.015).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Garland et al. 1993 source

  • May combine two claims.

    Findingown data
    § Additional information

    Total RSD variation explained is 0.513 for all raptors and 0.398 for territorial raptors.

    “Total 0.513 0.398”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data
    § Relative importance of ecological factors

    Territoriality and territory size explained more absolute RSD variation in partial regressions than did the structural complexity of hunting habitat, even though their regression coefficients were non-significant in multiple linear models.

    “Territoriality and territory size explained more absolute RSD variation in partial regressions than did the structural complexity of hunting habitat (Fig. 3), even though their regression coefficients were non-significant in multiple linear models.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data
    § Additional information

    Prey agility and hunting habitat are significant predictors of RSD, and models accounting for phylogenetic relationships show better fits than non-phylogenetic models.

    “Results qualitatively coincide with those yielded by OLS and PGLS models in identifying prey agility and hunting habitat as significant predictors and, models accounting for phylogenetic relationships as showing better fits than non-phylogenetic models.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data
    § Additional information

    Prey agility explains 0.433 of RSD variation in all raptors; hunting habitat 0.108; territoriality 0.160; territory size 0.188.

    “Prey agility 0.433 0.292 Hunting habitat 0.108 0.058 Territoriality 0.160 Territory size 0.188”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data
    § Territoriality and territory size

    The evolution of RSD has been slow and subject to evolutionary inertia, with closely related species showing RSD values more similar than expected at random.

    “These parameters,and which fitted for model residuals, indicate that the evolution of RSD has been slow and subject to evolutionary inertia, with closely related species showing RSD values more similar than can be expected at random.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation
    § Introduction

    Large prey cannot be managed by chicks until they reach an advanced age, delaying the time at which females resume hunting.

    “Large preys cannot be managed by the chicks until they reach an advanced age, delaying the time at which females resume to hunting (Sonerud et al. 2014a, b).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Sonerud et al. 2014a, b

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

  • Classified as probably not a substantial claim.

    Premisecitation
    § Introduction

    Raptors generally show female-biased sexual size dimorphism, an opposite trend to most birds and mammals, termed reversed sexual dimorphism (RSD).

    “Raptors generally show female-biased sexual size dimorphism, an opposite trend to what is observed in most bird and mammal species, thus usually termed reversed sexual dimorphism (hereafter RSD) (Amadon 1959;Andersson and Norberg 1981;Székely et al. 2007).”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites Amadon 1959

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

    • cites Andersson and Norberg 1981 source
    • cites Székely et al. 2007 source

  • Classified as probably not a substantial claim.

    Study design and conductcitation
    § Phylogenetic analyses

    The study accounted for phylogenetic autocorrelation by comparing OLS models with PGLS models.

    “To account for phylogenetic autocorrelation, we compared the results of the abovementioned OLS models with those of phylogenetic generalized least squares (PGLS) models (Freckleton et al. 2002).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Freckleton et al. 2002

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

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

    Premisecitation
    § Introduction

    In raptors, the female usually incubates, broods and feeds the nestlings until they can feed themselves unassisted, while the male provides food for the family.

    “It is well known that in raptors, the female usually incubates, broods and feeds the nestlings, until they can feed themselves unassisted, while the male provides food for the family (Newton 1979).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Newton 1979

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

  • Classified as probably not a substantial claim.

    Study design and conductnone given
    § Introduction

    The study takes into account the phylogenetic non-independence among raptor species in bivariate and multiple regression analyses.

    “We take into account the phylogenetic non-independence among raptor species, both when we explore bivariate relationships of RSD against each proxy and when we test these hypotheses in a multiple regression setting.”
    Quote in the paperSubstantial claim

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

    Premisecitation
    § Introduction

    Most raptor species (75% of the genera) are territorial during the breeding season.

    “Most raptor species (75% of the genera) are territorial during the breeding season (Newton 1979;del Hoyo et al. 1994;Ferguson-Lees and Christie 2001;Rebollo et al. 2017).”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites Newton 1979

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

    • cites del Hoyo et al. 1994

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

    • cites Ferguson-Lees and Christie 2001

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

  • Probably not a substantial claim: may not pass S2 (checkable). May combine two claims.

    Premisecitation
    § Introduction

    The mechanisms favouring RSD remain elusive, partly because several potential drivers of RSD are yet to be evaluated.

    “However, despite the abundant literature on RSD, the mechanisms favouring this trait remain elusive (Ferguson-Lees and Christie 2001;Sonerud et al. 2013;Friedman and Remeš 2016) partly because several potential drivers of RSD are yet to be evaluated.”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites Ferguson-Lees and Christie 2001

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

    • cites Sonerud et al. 2013

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

    • cites Friedman and Remeš 2016

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

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

    Premisecitation
    § Introduction

    RSD varies widely among raptor species; some species show barely noticeable differences between sexes, while in others females are twice as heavy as males.

    “Even so, RSD varies widely among different species of raptors.While some species show barely noticeable differences between sexes, in others, females are twice as heavy as their partners (Newton 1979).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Newton 1979

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

  • May combine two claims.

    Interpretationcitation
    § Hunting habitat structure

    During this period the male bears nearly sole responsibility for hunting, leading the male to be more strongly selected for small size than the female.

    “During this period the male bears nearly sole responsibility for hunting, leading the male to be more strongly selected for small size than the female (Ferguson-Lees and Christie 2001;Sonerud et al. 2014a, b).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites Ferguson-Lees and Christie 2001

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

    • cites Sonerud et al. 2014a, b

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

  • May combine two claims.

    Premisecitation
    § Territoriality and territory size

    Krüger's (2005) comparative study of 510 species of diurnal raptors and owls found strong support for male reduction and little support for female enlargement.

    “These results agree with Krüger's (2005) who found strong support for male reduction and little support for female enlargement in a comparative study comprising 510 species of diurnal raptors and owls.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Krüger's (2005) source

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

    Interpretationown data
    § Territoriality and territory size

    Based on our present findings, the selective pressures induced by all the predictors analysed here favour a strong reduction in male size, which would explain the evolution of RSD in raptors.

    “Based on our present findings, we can hypothesise that the selective pressures induced by all the predictors analysed here favour a strong reduction in male size, which would explain the evolution of RSD in raptors.”
    Quote in the paperSubstantial claim

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

    Interpretationown data
    § Territoriality and territory size

    Only habitats of greater structural complexity exert sufficient selective pressure to drive RSD.

    “This may indicate that only habitats of greater structural complexity exert sufficient selective pressure to drive RSD.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S1 (asserted), S4 (based). May combine two claims.

    Interpretationnone given
    § Territoriality and territory size

    Territorial species could experience extra selective pressures related to nesting in relation to non-territorial raptors, and these additional pressures may promote RSD.

    “These hypotheses propose that territorial species could experience extra selective pressures related to nesting in relation to non-territorial raptors.These additional pressures may promote RSD.”
    Quote in the paperNot a substantial claim

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

    Interpretationreasoning
    § Territoriality and territory size

    In these female disputes, size and strength should be most important for intimidating and expelling competitors from the feeding area, which would favour larger females.

    “In this case, size and strength should be most important for intimidating and expelling competitors from the feeding area, which would favour larger females.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationown data
    § Discussion

    RSD in diurnal raptors positively correlates with the structural complexity of the hunting habitat, as well as with territoriality.

    “Our results, for the first time, provide empirical evidence that RSD in diurnal raptors positively correlates with the structural complexity of the hunting habitat, as well as with territoriality.”
    Quote in the paperSubstantial claim

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

    Premisenone given
    § Territoriality and territory size

    Prior works failed to propose mechanisms to explain how intra-sexual competition for a territory may have influenced the body size of both sexes.

    “Those works failed to propose mechanisms to explain how intra-sexual competition for a territory may have influenced the body size of both sexes.”
    Quote in the paperNot a substantial claim

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

    Interpretationreasoning
    § Territoriality and territory size

    Disputes between females, which take place near the ground over smaller areas than the entire nesting territory, are resolved through aggressive displays with or without physical contact.

    “We suggest that these disputes between females, which take place near the ground over smaller areas than the entire nesting territory, are resolved through aggressive displays with or without physical contact.”
    Quote in the paperNot a substantial claim

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

    Interpretationreasoning
    § Territoriality and territory size

    Larger and stronger females should have a competitive advantage in acquiring territories, increasing their chances of breeding.

    “Contrary to what is observed in males, larger and stronger females should have a competitive advantage in acquiring territories, increasing their chances of breeding.”
    Quote in the paperNot a substantial claim

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

    Interpretationreasoning
    § Territoriality and territory size

    Another nonexclusive reason for increasing RSD with increasing territory size would select for small male body size due to energetic costs, i.e., longer movements during foraging in larger territories.

    “Another nonexclusive reason for increasing RSD with increasing territory size would select for small male (provider of prey) body size due to energetic costs, i.e., longer movements during foraging in the larger territories.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Premisecitation
    § Territoriality and territory size

    In species equipped with harmful weapons like talons, agility is more important than size and strength, where agility is defined as manoeuvrability and the ability to ascend rapidly to take an advantageous position above the opponent.

    “In species equipped with harmful weapons like talons, agility is more important than size and strength, where agility is defined as manoeuvrability and the ability to ascend rapidly in order to take up an advantageous position above the opponent (Widén 1984).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Widén 1984 source

  • Probably not a substantial claim: may not pass S1 (asserted), S3 (load-bearing), S4 (based).

    Interpretationnone given
    § Territoriality and territory size

    The longer the female is confined to the nest, the greater the RSD values.

    “time, the longer the female is confined to the nest, which would in turn lead to greater RSD values.”
    Quote in the paperNot a substantial claim

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

    Study design and conductcitation
    § Territoriality and territory size

    Collinearity among predictors does not affect regression coefficients in the OLS models, as indicated by condition numbers smaller than five.

    “Condition number (CN) was calculated for OLS models; values smaller than five indicate that collinearity among predictors does not affect regression coefficients(Belsley 1991).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Belsley 1991

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

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

    Interpretationreasoning
    § Territoriality and territory size

    Smaller and more agile males should outcompete their congeners due to their higher probability of obtaining a territory to breed and leave offspring.

    “Consequently, smaller and more agile males should outcompete their congeners due to their higher probability of obtaining a territory to breed and leave offspring.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationown data
    § Relative importance of ecological factors

    Species feeding on agile prey inside complex habitats may show the greatest RSD, and the selective pressures exerted by prey agility and habitat complexity may be cumulative.

    “This result suggests that, species feeding on agile prey inside complex habitats may show the greatest RSD, and thus, that the selective pressures exerted by prey agility and habitat complexity may be cumulative.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data
    § Discussion

    The associations found do not seem to be affected by the evolutionary relatedness among species; they seem more likely to have appeared as an adaptive response to the ecological factors on which this study focused.

    “The associations we find do not seem to be affected by the evolutionary relatedness among species; they seem more likely to have appeared as an adaptive response to the ecological factors on which this study focused.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning
    § Territoriality and territory size

    The evolution of RSD in diurnal raptors reflects primarily a strong reduction in male size, together with a possible weaker enlargement of females in some species.

    “We propose that the evolution of RSD in diurnal raptors reflects primarily a strong reduction in male size, together with a possible weaker enlargement of females in some species.”
    Quote in the paperSubstantial claim
41 of 41

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.

  • The 75-species model's reported R2 and adjusted R2 do not agree

    Minor

    The partial-regression table reports a total R2 of 0.513 for 75 species. For the stated three-predictor OLS model, that gives an adjusted R2 of about 0.492, not the 0.500 reported in Table 2.

1 of 1

Cites

Flagged first, then by citations

Research works printed but not linked: 8

  1. Amadon D., 1959, The significance of sexual differences in size among birds, Proc. Am. Phil. Soc., 103, 531
  2. del Hoyo J., 1994, Handbook of the birds of the world
  3. Ferguson‐Lees J., 2001, Raptors of the world
  4. Newton I., 2003, Population regulation in birds: is there anything new since David Lack?, Avian Sci, 3, 75
  5. Orme D., 2013, The caper package: comparative analysis of phylogenetics and evolution in R
  6. Palmqvist P., 1996, Relación entre peso corporal, tamaño del territorio, tamaño de puesta y tiempo de desarrollo en algunas rapaces del Paleártico Occidental, Bol. R. Soc. Esp. Hist. Nat. Secc. Biol., 92, 47
  7. Patterson I. J., 1980, Territorial behaviour and the limitation of population density, Ardea, 68, 53
  8. Pérez‐Camacho L., 2018, Data from: Structural complexity of hunting habitat and territoriality increase the reversed sexual size dimorphism in diurnal raptors, Dryad Digital Repository

Cited by

Sorted by citations

Related

Authors
Pérez‐Camacho, L., Martínez‐Hesterkamp, S., Rebollo, S., García‐Salgado, G., & Morales‐Castilla, I.
Affiliations
  • Universidad de Alcalá (ES)
  • Harvard University (US)
ORCID
Venue
Journal of Avian Biology
Publisher
Wiley
Published
2018-10
Volume
49
Issue
10
ISSN
  • 0908-8857 (ISSN-L)
  • 1600-048X
DOI
10.1111/jav.01745
OpenAlex
W2811255526
Semantic Scholar
047bddb881e050569799bb21b8eff30241daf13b
Cited by
18
References
53
Citations by year
2026: 1 · 2025: 1 · 2024: 6 · 2022: 4 · 2021: 3 · 2020: 3
FWCI
1.25
Type
journal article
Language
en
Open access
Licence
Locations
  • Journal of Avian Biology (publishedVersion)
  • e_Buah (acceptedVersion, cc-by-nc-nd)
  • LA Referencia (Red Federada de Repositorios Institucionales de Publicaciones Científicas) (submittedVersion, cc-by-nc-nd)
Funders
  • Peregrine Fund
  • Ministerio de Economía y Competitividad
Topics
  • Life Sciences › Agricultural and Biological Sciences › Ecology, Evolution, Behavior and Systematics › Animal Behavior and Reproduction
  • Physical Sciences › Environmental Science › Ecology › Avian ecology and behavior
  • Physical Sciences › Mathematics › Geometry and Topology › Morphological variations and asymmetry
Keywords
reversed sexual size dimorphism, diurnal raptors, habitat structural complexity, territoriality, territory size, prey type, body size evolution, Cathartidae, Pandionidae, Accipitridae, falcons, spatial niche

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 2026-10-12.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-12.

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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