Food availability and predation risk, rather than intrinsic attributes are the main factors shaping the reproductive decisions of a long-lived predator

Sarah R Hoy, Alexandre Millon, Steve J. Petty, D. Philip Whitfield, Xavier Lambin

Research output: Contribution to journalArticle

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Abstract

Deciphering the causes of variation in reproductive success is a fundamental issue in ecology, as the number of offspring produced is an important driver of individual fitness and population dynamics. Little is known however, about how different factors interact to drive variation in reproduction, such as whether an individual's response to extrinsic conditions (e.g. food availability or predation) varies according to its intrinsic attributes (e.g. age, previous allocation of resources towards reproduction).

We used 29 years of reproductive data from marked female tawny owls and natural variation in food availability (field vole) and predator abundance (northern goshawk) to quantify the extent to which extrinsic and intrinsic factors interact to influence owl reproductive traits (breeding propensity, clutch size and nest abandonment).

Extrinsic and intrinsic factors appeared to interact to affect breeding propensity (which accounted for 83% of the variation in owl reproductive success). Breeding propensity increased with vole density, although increasing goshawk abundance reduced the strength of this relationship. Owls became slightly more likely to breed as they aged, although this was only apparent for individuals who had fledged chicks the year before.

Owls laid larger clutches when food was more abundant. When owls were breeding in territories less exposed to goshawk predation, 99.5% of all breeding attempts reached the fledging stage. In contrast, the probability of breeding attempts reaching the fledging stage in territories more exposed to goshawk predation depended on the amount of resources an owl had already allocated towards reproduction (averaging 87.7% for owls with clutches of 1-2 eggs compared to 97.5% for owls with clutches of 4-6 eggs).

Overall, our results suggested that changes in extrinsic conditions (predominantly food availability, but also predator abundance) had the greatest influence on owl reproduction. In response to deteriorating extrinsic conditions (fewer voles and more goshawks) owls appeared to breed more frequently, but allocated fewer resources per breeding attempt. However, intrinsic attributes also appeared to have a relatively small influence on how an individual responded to variation in extrinsic conditions, which indicates that reproductive decisions were shaped by a complex series of extrinsic and intrinsic trade-offs.

Original languageEnglish
Pages (from-to)892-902
Number of pages11
JournalJournal of Animal Ecology
Volume85
Issue number4
Early online date3 May 2016
DOIs
Publication statusPublished - Jul 2016

Fingerprint

predation risk
Strigiformes
food availability
breeding
predator
predation
predators
fledging
reproductive success
resource
egg
clutch size
decision
attribute
breeds
Accipiter gentilis
population dynamics
nest
fitness
ecology

Keywords

  • Accipiter gentilis
  • breeding decisions
  • breeding propensity
  • clutch size
  • juvenile survival
  • life-history trade-offs
  • northern goshawk
  • reproductive strategies
  • Strix aluco
  • tawny owl

Cite this

Food availability and predation risk, rather than intrinsic attributes are the main factors shaping the reproductive decisions of a long-lived predator. / Hoy, Sarah R; Millon, Alexandre; Petty, Steve J.; Whitfield, D. Philip; Lambin, Xavier.

In: Journal of Animal Ecology, Vol. 85, No. 4, 07.2016, p. 892-902.

Research output: Contribution to journalArticle

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abstract = "Deciphering the causes of variation in reproductive success is a fundamental issue in ecology, as the number of offspring produced is an important driver of individual fitness and population dynamics. Little is known however, about how different factors interact to drive variation in reproduction, such as whether an individual's response to extrinsic conditions (e.g. food availability or predation) varies according to its intrinsic attributes (e.g. age, previous allocation of resources towards reproduction).We used 29 years of reproductive data from marked female tawny owls and natural variation in food availability (field vole) and predator abundance (northern goshawk) to quantify the extent to which extrinsic and intrinsic factors interact to influence owl reproductive traits (breeding propensity, clutch size and nest abandonment).Extrinsic and intrinsic factors appeared to interact to affect breeding propensity (which accounted for 83{\%} of the variation in owl reproductive success). Breeding propensity increased with vole density, although increasing goshawk abundance reduced the strength of this relationship. Owls became slightly more likely to breed as they aged, although this was only apparent for individuals who had fledged chicks the year before.Owls laid larger clutches when food was more abundant. When owls were breeding in territories less exposed to goshawk predation, 99.5{\%} of all breeding attempts reached the fledging stage. In contrast, the probability of breeding attempts reaching the fledging stage in territories more exposed to goshawk predation depended on the amount of resources an owl had already allocated towards reproduction (averaging 87.7{\%} for owls with clutches of 1-2 eggs compared to 97.5{\%} for owls with clutches of 4-6 eggs).Overall, our results suggested that changes in extrinsic conditions (predominantly food availability, but also predator abundance) had the greatest influence on owl reproduction. In response to deteriorating extrinsic conditions (fewer voles and more goshawks) owls appeared to breed more frequently, but allocated fewer resources per breeding attempt. However, intrinsic attributes also appeared to have a relatively small influence on how an individual responded to variation in extrinsic conditions, which indicates that reproductive decisions were shaped by a complex series of extrinsic and intrinsic trade-offs.",
keywords = "Accipiter gentilis, breeding decisions, breeding propensity, clutch size, juvenile survival, life-history trade-offs, northern goshawk, reproductive strategies, Strix aluco, tawny owl",
author = "Hoy, {Sarah R} and Alexandre Millon and Petty, {Steve J.} and Whitfield, {D. Philip} and Xavier Lambin",
note = "Acknowledgements We thank B. Sheldon and two anonymous reviewers for all their helpful comments on a previous version of the manuscript. Our thanks also go to M. Davison, B. Little, P. Hotchin, D. Anderson and all other field assistants for their help with data collection and Forest Enterprise, particularly Tom Dearnley and Neville Geddes for facilitating work in Kielder Forest. We are also grateful to C. Sutherland for his help and advice on statistical analyses. This work was partly funded by Natural Research Limited and a Natural Environment Research Council studentship NE/J500148/1 to SH and grant NE/F021402/1 to XL. Forest Research funded all the fieldwork on goshawks, tawny owls and field voles during 1973-1996. In addition, we are grateful to English Nature and the BTO for issuing licences to visit goshawk nest sites.",
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AU - Hoy, Sarah R

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AU - Petty, Steve J.

AU - Whitfield, D. Philip

AU - Lambin, Xavier

N1 - Acknowledgements We thank B. Sheldon and two anonymous reviewers for all their helpful comments on a previous version of the manuscript. Our thanks also go to M. Davison, B. Little, P. Hotchin, D. Anderson and all other field assistants for their help with data collection and Forest Enterprise, particularly Tom Dearnley and Neville Geddes for facilitating work in Kielder Forest. We are also grateful to C. Sutherland for his help and advice on statistical analyses. This work was partly funded by Natural Research Limited and a Natural Environment Research Council studentship NE/J500148/1 to SH and grant NE/F021402/1 to XL. Forest Research funded all the fieldwork on goshawks, tawny owls and field voles during 1973-1996. In addition, we are grateful to English Nature and the BTO for issuing licences to visit goshawk nest sites.

PY - 2016/7

Y1 - 2016/7

N2 - Deciphering the causes of variation in reproductive success is a fundamental issue in ecology, as the number of offspring produced is an important driver of individual fitness and population dynamics. Little is known however, about how different factors interact to drive variation in reproduction, such as whether an individual's response to extrinsic conditions (e.g. food availability or predation) varies according to its intrinsic attributes (e.g. age, previous allocation of resources towards reproduction).We used 29 years of reproductive data from marked female tawny owls and natural variation in food availability (field vole) and predator abundance (northern goshawk) to quantify the extent to which extrinsic and intrinsic factors interact to influence owl reproductive traits (breeding propensity, clutch size and nest abandonment).Extrinsic and intrinsic factors appeared to interact to affect breeding propensity (which accounted for 83% of the variation in owl reproductive success). Breeding propensity increased with vole density, although increasing goshawk abundance reduced the strength of this relationship. Owls became slightly more likely to breed as they aged, although this was only apparent for individuals who had fledged chicks the year before.Owls laid larger clutches when food was more abundant. When owls were breeding in territories less exposed to goshawk predation, 99.5% of all breeding attempts reached the fledging stage. In contrast, the probability of breeding attempts reaching the fledging stage in territories more exposed to goshawk predation depended on the amount of resources an owl had already allocated towards reproduction (averaging 87.7% for owls with clutches of 1-2 eggs compared to 97.5% for owls with clutches of 4-6 eggs).Overall, our results suggested that changes in extrinsic conditions (predominantly food availability, but also predator abundance) had the greatest influence on owl reproduction. In response to deteriorating extrinsic conditions (fewer voles and more goshawks) owls appeared to breed more frequently, but allocated fewer resources per breeding attempt. However, intrinsic attributes also appeared to have a relatively small influence on how an individual responded to variation in extrinsic conditions, which indicates that reproductive decisions were shaped by a complex series of extrinsic and intrinsic trade-offs.

AB - Deciphering the causes of variation in reproductive success is a fundamental issue in ecology, as the number of offspring produced is an important driver of individual fitness and population dynamics. Little is known however, about how different factors interact to drive variation in reproduction, such as whether an individual's response to extrinsic conditions (e.g. food availability or predation) varies according to its intrinsic attributes (e.g. age, previous allocation of resources towards reproduction).We used 29 years of reproductive data from marked female tawny owls and natural variation in food availability (field vole) and predator abundance (northern goshawk) to quantify the extent to which extrinsic and intrinsic factors interact to influence owl reproductive traits (breeding propensity, clutch size and nest abandonment).Extrinsic and intrinsic factors appeared to interact to affect breeding propensity (which accounted for 83% of the variation in owl reproductive success). Breeding propensity increased with vole density, although increasing goshawk abundance reduced the strength of this relationship. Owls became slightly more likely to breed as they aged, although this was only apparent for individuals who had fledged chicks the year before.Owls laid larger clutches when food was more abundant. When owls were breeding in territories less exposed to goshawk predation, 99.5% of all breeding attempts reached the fledging stage. In contrast, the probability of breeding attempts reaching the fledging stage in territories more exposed to goshawk predation depended on the amount of resources an owl had already allocated towards reproduction (averaging 87.7% for owls with clutches of 1-2 eggs compared to 97.5% for owls with clutches of 4-6 eggs).Overall, our results suggested that changes in extrinsic conditions (predominantly food availability, but also predator abundance) had the greatest influence on owl reproduction. In response to deteriorating extrinsic conditions (fewer voles and more goshawks) owls appeared to breed more frequently, but allocated fewer resources per breeding attempt. However, intrinsic attributes also appeared to have a relatively small influence on how an individual responded to variation in extrinsic conditions, which indicates that reproductive decisions were shaped by a complex series of extrinsic and intrinsic trade-offs.

KW - Accipiter gentilis

KW - breeding decisions

KW - breeding propensity

KW - clutch size

KW - juvenile survival

KW - life-history trade-offs

KW - northern goshawk

KW - reproductive strategies

KW - Strix aluco

KW - tawny owl

U2 - 10.1111/1365-2656.12517

DO - 10.1111/1365-2656.12517

M3 - Article

VL - 85

SP - 892

EP - 902

JO - Journal of Animal Ecology

JF - Journal of Animal Ecology

SN - 0021-8790

IS - 4

ER -