Regulation of Irruptive Migratory Behavior of Red Crossbills Loxia curvirostra

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Regulation of Irruptive Migratory Behavior of Red
Crossbills (Loxia curvirostra)

• Navdeep Brar
• McNair Scholars Program
• Department of Psychology
• Dr. Thomas Hahn Jamie Cornelius
• Department of Neurobiology, Physiology, and
  Behavior
• University of California, Davis

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Migration is Essential For Survival

• Food supply varies in space and time
• Migration permits birds to cope with these
  fluctuations in food supply

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Types of Migration
Seasonal Site faithful, high spatial and temporal
food predictability White-crowned Sparrow
Nomadic/Irruptive Not site faithful, low spatial
and temporal food predictability Crossbills
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Study OrganismRed Crossbills, Loxia curvirostra

• Irruptive, nomadic songbirds of northern
  coniferous forests
• Specialize on conifer seeds
• these seeds are distributed
• unpredictability in space and time

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Study OrganismRed Crossbills, Loxia curvirostra

• Not site faithful
• Likely have evolved to regulate their migratory
  behaviors through variety of factors
• Food supply, weather, and body condition
• Unpredictable food supply may be a stimulus for
  crossbill migratory movements

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Hypotheses

• 1) Food restriction will stimulate increased
  activity, indicating a increased irruptive
  migratory disposition
• 2) Food restriction will increase corticosterone
  responsiveness to stressors

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Hypothesis 1 Food Reduction and Activity
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Recording Activity

• Activity is typically measured by computerized
  perches
• These perches are hooked up to a computer and
  record hopping movements
• Seasonal migrants move at night
• Crossbills do not migrate at night
• They perform hopping, climbing, and flying
  movements
• We videotaped the Crossbills in order to fully
  record their movements

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Methods

• Ten Red Crossbills
• were collected on the
• Olympic Peninsula in
• the state of Washington
• and were brought back to
• UC Davis for the experiment

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Control
Roudybush
Fixed limited sunflower seed
allotment
Food Reduced
Roudybush
75 of Roudybush
Fixed limited sunflower seed
allotment
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0
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Control bleed
Filming begins
Experimental bleed
Food reduction begins
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• All individuals were filmed for two hours in the
  morning and two hours in the afternoon
• Video tapes were broken up into 15 minute
  intervals and scored for activity
• When the individual crossed the divider on the
  screen one activity event was recorded
• Data were analyzed using repeated measures ANOVA

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Possible Outcomes To Food Reduction

• Decreased activity
• Increased activity
• No effect on activity

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Repeated Measures ANOVA, treatment x sampling
date interaction is nearly significant, p.07
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Fat and Mass both tended to decrease in food
reduced and control birdsNo significant
difference between treatments or sampling dates
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• Hypothesis 2 Food Reduction and Corticosterone

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Possible Hormonal MechanismsCorticosterone

• A steroidal metabolic and stress hormone
• Released from adrenal gland
• Involved in maintaining metabolic homeostasis
• Involved in short and long term response to
  stress
• Mobilizes glucose, promotes escape behaviors and
  foraging, decreases territorial and reproductive
  behaviors

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Methods

• We measured corticosterone responsiveness to
  handling stress
• Corticosterone responsiveness is measured via
  series of blood draws
• Within 3 minutes of handling (baseline) and
  5,10,30,60 minutes (handling stress levels)
• Use Enzyme-linked immunoassay (EIA) to determine
  CORT levels in blood samples

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No significant difference in baseline levels of
CORT
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Maximum CORT was significantly higher in food
reduced birds.Repeated Measures ANOVA
significant treatment effect, plt.05nearly
significant treatment by sampling date
interaction, p.06
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Conclusion Hypothesis 1Food and Activity

• Consistent with our first hypothesis
• Activity increased in food-reduced individuals
• Consistent with the pattern of irruptive
  migration, which is stimulated by food supply

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Conclusion Hypothesis 2 Food and CORT

• Baseline levels of corticosterone were unaffected
  by food restriction
• Food reduction enhanced handling CORT
  responsiveness

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Combining Hypotheses 1 and 2 Physiology and
Behavior

• Positive relationship between CORT and activity
  levels
• Relationship somewhat weak, but higher sample
  size may strengthen relationship
• This is a preliminary study

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Next Steps

• Different types of food reductions
• (i.e. preferred vs. non-preferred foods, use
  actual cones, etc)
• Specificity of the effect on behavior Really
  migratory activity?

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Acknowledgements

• Thomas Hahn
• Department of Neurobiology, Physiology, and
  Behavior
• Jamie Cornelius
• Department of Neurobiology, Physiology, and
  Behavior
• McNair Scholars Program
• University of California, Davis

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Regulation of Irruptive Migratory Behavior of Red
Crossbills (Loxia curvirostra)

• Navdeep Brar
• McNair Scholars Program
• Department of Psychology
• Dr. Thomas Hahn Jamie Cornelius
• Department of Neurobiology, Physiology, and
  Behavior
• University of California, Davis