Males and females differentially adjust vigilance levels as group size increases: effect on optimal group size

Whiteside, Mark; Langley, Ellis J. G.; Madden, Joah R.

doi:10.1016/j.anbehav.2016.04.025

Cited by 21 publications

(19 citation statements)

References 59 publications

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“…This higher collective vigilance would allow quicker detection of sudden departures and thus a reduction in reaction times in larger groups. In other species, levels of collective vigilance often are higher in larger groups (Ebensperger, Hurtado, & Ramos-Jiliberto, 2006;Pays, Sirot, & Fritz, 2012;Whiteside, Langley, & Madden, 2016). Data on collective vigilance in sparrow groups are needed to assess this hypothesis more fully.…”

Section: Discussionmentioning

confidence: 99%

Spread of false alarms in foraging flocks of house sparrows

2017

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In group‐foraging species with no alarm signals, the sudden departure of neighbours can be used to inform the rest of the group about the detection of a threat. However, sudden departures are ambiguous because they can be triggered by factors unrelated to predator detection. We evaluated how animals react to the sudden departure of neighbours in groups of foraging house sparrows (Passer domesticus). We focussed on false alarms that occurred for no apparent reasons to us because predation attempts were not frequent. Three factors can explain how the sudden departure of a neighbour can influence reaction times, namely group size, the distance between neighbours, and predation risk. We predicted reaction times to be longer in larger groups where individual vigilance levels are low, and when group members are further apart and cannot easily monitor each other. In addition, we expected reaction times to be longer when predation risk is lower. Departures that are more temporally clumped are also expected to be less ambiguous and should trigger faster reaction times. Our results show that sparrows reacted faster, not more slowly, to the sudden departures of neighbours in larger groups, and, as predicted, more slowly when neighbours were more distant from each other. Reaction times were longer in one of the two study years in which predation risk was deemed lower. Sparrows reacted more quickly when earlier departures were more temporally clumped. The results thus provided partial support for the predictions, and future work is needed to assess how individuals react to fleeing responses by their neighbours in species with no alarm signals.

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Section: Discussionmentioning

confidence: 99%

Spread of false alarms in foraging flocks of house sparrows

2017

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“…All observations were conducted from inside a vehicle at a distance of > m (e.g. Whiteside et al 2016a) either during the first 2 hours after first light or the final 2 hours before last light (Taber 1949). We recorded the total time we observed the birds, the time spent foraging and the number of foraging bouts they performed.…”

Section: Manuscript To Be Reviewedmentioning

confidence: 99%

“…In species where sex differences in time spent foraging are observed it is often attributed to their investment in reproduction (Lewis et al 2002) and differences in parental care roles (Gray & Hamer 2001;Thaxter et al 2009). Although female pheasants will forage more than males prior to nesting Whiteside et al 2016a), this occurs in early spring after hens have abandoned their segregated winter aggregations and joined harems.…”

Section: During This Period Females May Not Discriminate Against Highmentioning

confidence: 99%

“…Specifically, during the late autumn and winter, females aggregate in same sex groups whereas males avoid both males and females (Whiteside et al 2018). Such segregation persists until early March Hill & Robertson 1988) when harems of females visit and eventually join territory-holding males, which likely reduces their harassment by other males (Ridley and Hill 1987) and allows females to decrease their vigilance levels and so increase time spent foraging (Whiteside et al 2016a), until they independently start to nest and incubate their eggs (Taber 1949). Pheasants become sexually dimorphic by three weeks of age (Whiteside et al 2017), and chicks in captivity (<8 weeks old) exhibit preference for their own sex (Whiteside et al 2017).…”

Section: Introductionmentioning

confidence: 99%

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Peer Review #1 of "Size dimorphism and sexual segregation in pheasants: tests of three competing hypotheses (v0.1)"

2018

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Fine scale sexual segregation outside of the mating season is common in sexually dimorphic and polygamous species, particularly in ungulates. A number of hypotheses predict sexual segregation but these are often contradictory with no agreement as to a common cause, perhaps because they are species specific. We explicitly tested three of these hypotheses which are commonly linked by a dependence on sexual dimorphism for animals which exhibit fine-scale sexual segregation; the Predation Risk Hypothesis, the Forage Selection Hypothesis, and the Activity Budget Hypothesis, in a single system the pheasant, Phasianus colchicus; a large, sedentary bird that is predominantly terrestrial and therefore analogous to ungulates rather than many avian species which sexually segregate. Over four years we reared 2400 individually tagged pheasants from one day old and after a period of 8-10 weeks we released them into the wild. We then followed the birds for 7 months, during the period that they sexually segregate, determined their fate and collected behavioural and morphological measures pertinent to the hypotheses. Pheasants are sexually dimorphic during the entire period that they sexually segregate in the wild; males are larger than females in both body size and gut measurements. However, this did not influence predation risk and predation rates (as predicted by the Predation Risk Hypothesis), diet choice (as predicted by the Forage Selection Hypothesis), or the amount of time spent foraging, resting or walking (as predicted by the Activity Budget Hypothesis). We conclude that adult sexual size dimorphism is not responsible for sexual segregation in the pheasant in the wild. Instead, we consider that segregation may be mediated by other, perhaps social, factors. We highlight the importance of studies on a wide range of taxa to help further the knowledge of sexual segregation.

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“…Specifically, during the late autumn and winter, females aggregate in same sex groups whereas males avoid both males and females ( Whiteside et al, 2018 ). Such segregation persists until early March ( Hill & Ridley, 1987 ; Hill & Robertson, 1988 ) when harems of females visit and eventually join territory-holding males, which likely reduces their harassment by other males ( Ridley & Hill, 1987 ) and allows females to decrease their vigilance levels and so increase time spent foraging ( Whiteside, Langley & Madden, 2016 ), until they independently start to nest and incubate their eggs ( Taber, 1949 ). Pheasants become sexually dimorphic by three weeks of age ( Whiteside et al, 2017 ), and chicks in captivity (<8 weeks old) exhibit preference for their own sex ( Whiteside et al, 2017 ).…”

Section: Introductionmentioning

confidence: 99%

Size dimorphism and sexual segregation in pheasants: tests of three competing hypotheses

Whiteside

Horik

Langley

et al. 2018

PeerJ

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Fine scale sexual segregation outside of the mating season is common in sexually dimorphic and polygamous species, particularly in ungulates. A number of hypotheses predict sexual segregation but these are often contradictory with no agreement as to a common cause, perhaps because they are species specific. We explicitly tested three of these hypotheses which are commonly linked by a dependence on sexual dimorphism for animals which exhibit fine-scale sexual segregation; the Predation Risk Hypothesis, the Forage Selection Hypothesis, and the Activity Budget Hypothesis, in a single system the pheasant, Phasianus colchicus; a large, sedentary bird that is predominantly terrestrial and therefore analogous to ungulates rather than many avian species which sexually segregate. Over four years we reared 2,400 individually tagged pheasants from one day old and after a period of 8–10 weeks we released them into the wild. We then followed the birds for 7 months, during the period that they sexually segregate, determined their fate and collected behavioural and morphological measures pertinent to the hypotheses. Pheasants are sexually dimorphic during the entire period that they sexually segregate in the wild; males are larger than females in both body size and gut measurements. However, this did not influence predation risk and predation rates (as predicted by the Predation Risk Hypothesis), diet choice (as predicted by the Forage Selection Hypothesis), or the amount of time spent foraging, resting or walking (as predicted by the Activity Budget Hypothesis). We conclude that adult sexual size dimorphism is not responsible for sexual segregation in the pheasant in the wild. Instead, we consider that segregation may be mediated by other, perhaps social, factors. We highlight the importance of studies on a wide range of taxa to help further the knowledge of sexual segregation.

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Males and females differentially adjust vigilance levels as group size increases: effect on optimal group size

Cited by 21 publications

References 59 publications

Spread of false alarms in foraging flocks of house sparrows

Spread of false alarms in foraging flocks of house sparrows

Peer Review #1 of "Size dimorphism and sexual segregation in pheasants: tests of three competing hypotheses (v0.1)"

Size dimorphism and sexual segregation in pheasants: tests of three competing hypotheses

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