Birds of Seabrook Island

COAST BIRDS
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ANECDOTES

  Energetics
 
 

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Migration
 
Skip to:   
   
Annual Cycles Breeding Migration Migration in Captive birds
  Activity Cages
  Operations Recorder (Activity)
  Actual Count Data
  Zugunruhe
Energetics and the Annual Cycle
Estimates
A Model for Control
References
   
 


Energetics and the Annual Cycle

  Way back when, I held individuals of 8 species of emberizines captive and studied them over two years. This image shows the annual cycle of caged White-throated Sparrows housed outdoors in Central Pennsylvania.
 
White-throated Sparrow
  The top bar shows development of the cloacal protuberance (CP), an external index to gonadal development. The next set of bars shows the seasonally separated periods of molt (M) - prenuptial and postnuptial molts. The first solid line shows the nocturnal activity (NA) in counts/hour for the individuals averaged over two years.
   Body weight (mass) (BW) is the next solid line. It tends to be high in winter and low in summer with a marked peak before spring migration - Body fat (BF) is measured visually and parallels weight. Energetic adaptations for migration include fat deposition as a fuel - fat has twice the caloric density of carbohydrate or protein and is not osmotically active so it is an ideal "gas" for flight.
   BC (Balance Coefficient) simply indicates whether the bird is gaining or loosing weight (mass).
   UC (Utilization Coefficient) indicates the amount of ingested food that is metabolized. It stays relatively constant at 75% suggesting no gain in energy by more efficient utilization - this value would change with seasonal diets if the bird were living freely. 
  The bottom four traces on this graph show the amounts of energy (in kcal/bird/day) used throughout the year. GE - top - (Gross Energy) is the total food energy eaten. EE - bottom - (Excretory Energy) is the total energy in the feces and urine. The difference is ME (Metabolizable Energy) represented by the middle trace. CE (Catabolized Energy) takes into account changes in body mass (storing or withdrawing energy) and is represented by open circles.
    White-throated Sparrows need more energy in winter than summer and increase their energy intake during the period of fat deposition in the spring in preparation for migration. The lowest requirements are during molt and the warmest period of the year.
       
     Many analyses can be performed using data from captives. In the final analysis, I have been interested in correlating these data with field observations and a comparison of metabolism estimated by both approaches culminates the previous section on banding.
   
  Estimated Metabolizable Energy (ME) is partitioned into: (1) existence energy, including costs attributable to (a) standard metabolism and varying body weight, efficiency, and photoperiod (bottom portion of shaded bars), (b) varying cloud cover and wind velocity (upper portion of shaded bars), and (c) thermoregulation (white bars); and (2) productive energy, including expenditures for (a) nocturnal activity (stippled bars), and (b) molt (black bars). Estimates based on the following equation. Abscissa scaled in months. Phenology based on data from captive males housed in central Pennsylvania. Average values for the entire year are given in the right-hand bar labeled SPECIES. Annual energy budget
 

ME = -4.49 + 0.175UC + 0.589log10(NA + 1.0) + 0.466BW - 0.229AT - 2358NH + 0.286FF - 0.0364PP + 0.278M ± 1.88
df = 8, 520, 0.005 > P; R2 = 0.63
where ME - Metabolizable Energy, UC = Utilization Coefficient, NA = Nocturnal Activity, BW = body mass in g, AT = Air Temperature (°F), NH = Cloud Cover in tenths, FF = Wind Velocity (MPH), PP = photoperiod in hours.

 
 

Estimates

      For more numbers than you probably need, the following table brings together the important energetic estimates for spring migration in the White-throated Sparrow.
   
Estimates
   
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A Model for Control

   
Control
    This model adds information from some studies in our laboratory on circadian rhythms and the controls of feeding and drinking to try to explain how various features of the annual cycle are causally mediated by proximate factors and the neural and endocrine systems of the bird as of 1972. There is no general consensus on any such model (and this one remains unpublished)... At that point, I had a choice of becoming a neurophysiologist or department Head - and, for better or worse, chose the latter. Fortunately. I enjoy watching birds in nature so the birds may ultimately be better off...
       
   

References

    Alterstam, T. 1982. Bird Migration. Translated by D. A. Christie, 1990. Cambridge
  University Press, Cambridge
Berthold, P. 2001. Bird Migration, A General Survey. 2nd. ed. Translated by H-G. Bauer
  and V. Westhead. Oxford University Press, Oxford
Gauthreaux, S. A., Jr. A portable ceilometer technique for studying low-level nocturnal
   migration.Bird-Banding 40: 309-320
Gauthreaux, S. A., Jr. 1971. A radar and direct visual study of passerine spring
  migration in southern Lousiana. Auk 88: 343-365
Gauthreaux, S. A., Jr. 1972. Behavioral responses of migrating birds to daylight and
   darkness: A radar and direct visual study. Wilson Bull. 84: 136-148
Greenberg, R. and P. P. Marra. 2005. Birds of Two Worlds. Johns Hopkins University
   Press, Baltimore
Helms, C. W. 1968. Food, fat, and feathers. Amer. Zool. 8: 151-167. (Also cited earlier)
Zimmerman, J. L. 1998 (Revised, original by F. C. Lincoln, 1936). Migration of Birds. US
    Fish and Wildlife Service Circular 16 (Internet)
       
    Banner - metabolism estimates (above).