Carolina Chickadee field metabolism and water flux

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Carolina Chickadee field metabolism and water flux

• From Field metabolism and water flux of Carolina
  Chickadees during breeding and nonbreeding
  seasons a test of the peak-demand and
  reallocation hypotheses (Condor 103 370-375)
• Presenter Nathan Thomas

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Introduction

• Energy expenditure, survival, and life history
  have complex relationships
  
• More complete understanding requires better
  information about time and energy allocation over
  an annual cycle
  
• Energy expenditure studies on free ranging birds
  have been focused on the reproductive cycle
  
• Due to relationship of reproduction on fitness
• More studies are needed during the non-breeding
  season, particularly winter
  
• High thermoregulatory costs
• Low food supplies
• Short day length
• How do energy budgets fluctuate over time (the
  annual cycle)?
  
• Two competing hypotheses

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In this corner we have

• Peak demand hypothesis
• Energy expenditure changes seasonally
• Highest during breeding season (feeding
  nestlings)
  
• Increased expenditure causes a decrease in
  survivorship
  
• For small passerines- still beneficial because
  survival to following breeding season quite low
  
• Minimize chance of mortality by working at 4X BMR
  (basal metabolic rate) or lower
  
• Above 4X detrimental effects accumulate-?
  mortality
  
• 3 possible reasons for 4X ceiling
• Limited food supply
• Central organs limit conversion of food into
  energy
  
• Peripheral organs limit conversion of energy into
  work
  
• Very few studies have compared energy usage
  seasonally

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and the competitor is

• Reallocation hypothesis
• Metabolic rate is constant over an annual cycle
• Winter demands higher thermoregulatory costs and
  increased foraging compared to the breeding
  season
  
• In contrast breeding occurs when food supplies
  are at a maximum and temperatures are moderate
  
• Energy saved by decreased foraging and very
  slight thermoregulatory costs (during breeding)
  are reallocated to breeding activities
  
• Both hypotheses have been supported over the
  years
  
• Many ecological issues associated with these
  hypotheses remain unexplored

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The study at hand

• Objective- test peak demand and reallocation
  hypotheses
  
• Measure energy expenditure and water flux in the
  Carolina Chickadee (Poecile carolinensis) using
  doubly labeled water (DLW)
  
• During breeding season- feeding older nestlings
• During nonbreeding season- high thermoregulatory
  demands
  
• Comparison with other parids (members of the
  family Paridae)
  
• FMR (field metabolic rate) was never before
  measured in the Carolina Chickadee (CC)
  
• Other parid studies found sustained MR below 4X
  but higher rates were found during breeding
  season
  
• One other study ever used the same population
  during both the breeding and nonbreeding seasons
  (Cooper 2000)
  
• Used time-activity budget

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Methods

• 12 woodlots in Crawford County, Ohio
• Flat agricultural landscape with small woodlots
• Northern edge of CC range
• May-June 1998 breeding season
• Mist-netted 6 chickadees while they were feeding
  nestlings (nestling age10 days)
  
• Energy expenditure maximum
• Nestlings fly at 13-17 days
• February-March 1999nonbreeding season
• Captured 6 chickadees feeding at sunflower seed
  feeders
  
• Used both mist nets and walk-in traps
• Air temperature recorded on days of capture

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Crawford County- Ohio
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• DLW used to measure CO2 production and rate of
  water flux
  
• Injected willing avian participants with
  deuterium and 18O
  
• Allowed equilibration (1 hr.)
• Drew blood (6- 15µl samples) from brachial vein
  on wing (see picture)
  
• Weighed, banded, and released birds
• Recaptured same birds close to 24 hrs. (range
  19-27 hrs.)
  
• Rebled, reweighed, and released birds again
• Analyzed blood samples for ratios
• Deuterium (2H) Hydrogen (1H)
• 18O 16O
• Each sample run three times

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Least sandpiper
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Calculations
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Statistical Analysis

• Body mass of individual birds between initial and
  final capture was analyzed using a paired t-test
  
• Body mass between breeding and nonbreeding birds
  (mean body mass) was analyzed using a 2 sample
  t-test
  
• Water flux and energy expenditure
• Complicated by differing body weights (? in
  winter)
  
• Fat deposition
• Increased muscle mass
• Hypertrophy of organs (due to ? thermoregulatory
  demand)
  
• Reported as whole animal per day (day-1), per day
  per gram (day-1g-1), and per day per g-x
  (day-1g-0.67)
  
• 2 sample t-tests used to compare water flux, CO2
  production, and FMR between seasons

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Results

• 6 breeding season and 6 nonbreeding season birds
• Average daily temperatures
• Breeding 20.21.2C (68.4F)
• Nonbreeding 1.11.2C (34F)
• Time between 1st and 2nd capture was not
  significantly different between seasons (P0.84,
  mean 23.60.4 hr.)
  
• Body mass
• Overall body mass did differ between seasons-
  nonbreeding season birds were significantly
  heavier (P0.04)
  
• Mass change () between captures was not sig.
  different from zero during either season (P0.12)

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• Water flux
• Influx (ml/day) was greater in breeding birds
  than nonbreeding (P
  gram, or per gram-0.67
  
• For whole bird 54 less water used during
  nonbreeding season
  
• CO2 production
• Significantly lower during breeding season than
  during nonbreeding (P0.01)
  
• FMR significantly lower during the breeding
  season as well (P
• Per bird the CC used 42 more energy/day in
  nonbreeding season than during breeding season
  (recall CC were heavier during winter)
  
• Recalculate to correct for body mass
• Still used 50 less water and metabolized 32
  more energy/day/gram of body mass
  
• Using log-log regression exponent CC used 51
  less water and 35 more energy/day/gram-0.67
  

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Compared to other parids

• Mass explained most of the variation between
  species (ß0.88, P
• Season explained very little of the variation
  (ß0.06, P
• Energy expenditure seems to be greater in
  nonbreeding season than in breeding, but..
  
• Caution is warranted
• Mass and season had a high correlation (r0.74)
  and Carolina Chickadees are the only parid thus
  far with FMR measured using DLW
  
• Extrapolation/Interpretation of other parids will
  have to wait for more supporting data

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Discussion

• Theory suggests MR should be at a maximum during
  the breeding season (? fitness)
  
• FMR during breeding should meet (reallocation) or
  exceed (peak demand) FMR for nonbreeding
  
• Results from this study do not support either
  hypothesis
  
• Recall FMR was higher during nonbreeding
• 2 other studies which did not support either
  hypothesis
  
• Weathers et. al. (1999)
• No correction for body mass despite mass
  difference
  
• Cooper (2000)
• Not a direct measure of FMR (time-activity
  budget)
  

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Increased energy expenditure during nonbreeding
season

• Significant occurred with and without a
  correction for body mass
  
• Body mass is important when comparing FMR between
  seasons
  
• Larger body size alone could account for ? MR
• Body size ? usually believed to be inert fat
• Some spp. show central body organ ? due to
  different diet and colder temperatures
  
• Central organs more metabolically expensive to
  maintain
  
• Amount of organ ? in chickadees is unknown
• FMR increase during nonbreeding season would not
  occur if fat alone increased
  
• Seasonal differences to cause increase
• Predation and food availability
• Varying amount of peripheral and central organ
  tissue
  
• Northern extreme of range for CC
• High thermoregulatory stress

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In conclusion

• FMR only known for CC and Great Tit during
  breeding but tit nonbreeding FMR unknown
  
• Willow Tit was found to have increased FMR
  further north in range
  
• No differences found between species in same
  study area
  
• Not enough data available for generalization
  across Paridae
  
• More information needed across annual cycle and
  at varying temperatures
  
• FMR always higher during breeding season
  according to peak demand hypothesis
  
• It assumes a static pattern of energy
  expenditure
  
• Energy expenditure is not static over time
• Studies investigating energy use over different
  seasons will help disclose patterns of
  fluctuating energy expenditure over time