Costs and Benefits Associated With Spatial Position in a Group

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Costs and Benefits Associated With Spatial
Position in a Group
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Spatial Position Effects on Foraging and
Protection from predators in Brown-Headed Cowbirds
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Position in group

• Individuals on edge
• More time spent with their head-up, scanning for
  predators
• Faster pecking rate

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Neighbor distance

• Pecking rate and scanning time
• Edge birds more influenced by neighbor distance
  than central birds

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Conclusion

• Edge individuals feel a greater predation risk
  and therefore can spend less time foraging
• To compensate, they forage at a faster rate.

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The scaled dove Columbia squammata

• Common bird widely distributed in Brazil and
  other Latin American countries.

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Raphael Igor Dias, 2006

• Explored the idea that peripheral individuals
  spend more time being vigilant and less time
  feeding.
• The Edge effect
• Peripheral individuals exposed-more risk of being
  on edge
• Middle individuals protected- information about
  predators from peripheral zone.

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• Campus of Brasília in central Brazil
• Aug July active searches carried out for free
  ranging flocks.
• Animals randomly chosen from the edge and the
  centre
• Data collected of scan rate and vigilance.
  Mann-whitney and Spearman correlation tests used
  to compare the duration of vigilance and foraging
  between the edge and the centre

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Feeding

• Eg Eiders
• Front edge position vs centrality
• Abundant food items vs rare food items
• Tradeoffs
• Hirsch (2007)

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Predation

• Eg Eiders
• Brood Coalitions
• Gull Predation
• Central females more aggressive
• Vigilance increases
• Resting, feeding, moving decreases
• Survival of brood NB
• Ost (2007)

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Thermoregulation

• Costs and benefits

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Where is warmest in a group?

• Away from wind
• Gilbert, C. 2008

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Where is warmest in a group?

• Second law of thermodynamics
• Dont be exposed to the outside
• Surrounded by individuals of a similar
  temperature

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Who gets to have the inside?

• Dominance
• Cucullata flocks
• Calf, K 2002

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Always dominance?

• Penguins- all get equal access to heat
• Gilbert C 2006

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Black-tailed Godwit

• Sleeping and vigilance
• Peeking behaviour
• Environmental conditions

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