Birds of Seabrook Island

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  Zugunruhe
 
 

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Migration
 
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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
 
 

Migration in Captive Birds

  Field studies of migration provide much information about timing and migratory behavior. It is also possible to study captive individuals...
 
 

Activity Cages

  Metabolism cage
An activity cage - two offset and counter weighted perches rest on microswitches that register each time a bird sits on the perch. In this enhanced cage setup, measured food is fed for a week after which feces and wastes are collected and separated and, using oxygen bomb calorimetry, the energetics of the individual can be determined. In the annual cycle diagram below, energetic results are presented for an entire year.
The graduated "Richter" tube on the right was used to measure water consumption in some studies.

Cage enclosure


This rack houses 10 cages and allows birds to be studied under different light regimes. Individuals can hear but not see other birds.

     
 

Operations Recorder (Activity)

 
 
Recorder
  At the end of the day, the 18" record from all 20 channels is cut and each channel separated. The appropriate strip is then mounted on a poster board below the record from the previous day. This gives an "actogram" like that to the right showing a considerable period of activity, including changing daylength and, during migration, the intense periods of nocturnal activity ("Zugunrhue") of each individual. Spring unrest
  An Esterline-Angus 20-channel event recorder. Each track is the record of a different bird. At its slowest speed (18"/day) individual hops cannot be determined but the time of activity and inactivity can be measured to about the nearest minute.
  Activity of a White-throated Sparrow between 8 March and 28 April, 1958. Each line is the activity for 24 hours beginning at noon and ending the following noon. Note that activity tends to be higher after sunrise and before sunset. On the night of 10-11 April, there is a period of activity around midnight and some a bit later. Then on the 13th, the individual begins to be active at night. This grows to include almost the entire night (with some decrease before sunset).
     
   

Actual Count Data

    Counters
Junco populations
Activity of two Dark-eyed Junco populations. Junco hyemalis hyemalis, latitudinal migrants (above), and J. h. carolinensis, an altitudinal migrant and resident of the southern Appalachians (below).
   Mean values are connected by lines. The dark bar extends three standard errors to each side of the mean and the open bar one standard deviation to each side of the mean. Non-overlap of the black bars suggests that the means are significantly different.
   This comparison shows that both populations show significant nocturnal activity but in the resident group (bottom) it is low at the beginning of the night and peaks later in the morning. Perhaps more importantly, the resident populations do not increase weight or fat during either migratory period and would have significant problems flying long distances without these reserves.
    A bank of counters, each connected to an activity cage. Pictures of the counter-bank can be used to determine hourly activity or total day/night counts, depending upon how the camera is set.
   Actual count data varies greatly. It is zero-limited on the low end (and zero-limited data are seldom distributed normally so statistical tests are difficult). The data are also highly variable - some birds crank out 50,000 counts/hour while most may show 1,000 or so counts/hour.
   In an attempt to normalize these data, we have use the [log (NA + 1)] transform (1 is added because there  is no log of 0).
   The results of count data are shown to the right from a study of resident and migratory junco populations done by Steve Calver in my laboratory in Georgia.
       
   

Zugunrhue

   
    Because nocturnal activity in caged birds begins at the same time wild birds are actually migrating in the spring, it is widely regarded as a manifestation of migratory drive and has been called Zugunruhe ("migratory restlessness"). Its intensity through the night is also reminiscent of flight patterns determined using radar or direct observation (above). However, this activity does continue beyond the end of both the normal spring and fall migratory periods. Nocturnal singing in breeding birds suggests that the patterns of wakefulness may, however, not be unusual. In the figure above showing the annual cycle, the inner circle suggests that these extensions may be adaptational - the bird would still be capable of moving at night if weather conditions become intolerable... My preference is to refer to the nocturnal activity of caged birds as nocturnal activity - begging the question of motivation.
       
    Banner - activity records of several birds (above).