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An observational study of the social and solitary behaviors of three pairs of Bali mynahs (Leucopsar rothschildi) at two breeding facilities in Bali, Indonesia
Results & Discussion
The nest-box scans are an important place to start since there was one particularly significant result that effected how all of the other graphs were calculated. The female in D27 spent significantly more time in her nest-box than any other bird, so to validate comparisons of other scans, they were calculated as average percentages of scans out of those where each bird was visible, rather than simply the average number of scans per hour. She could still have been adjusting to her new environment, or to her relatively new partner. The male, who did not spend nearly as much time in the nest-box, had been paired in that same cage previously. In addition, the D27 birds may have been either breeding or nesting.
Allogrooming bouts showed significant differences between cages and between males and females (Figure 4). In every cage for which bouts were recorded, females initiated bouts of allogrooming more than males, and overall this difference between the sexes was significant. Cage D27 birds also groomed each other far less than the other pairs, once again possibly as a result of the birds still adjusting to one another, or possibly just not getting along.
Head-bobbing bouts showed very different results. The males from each cage head-bobbed at almost exactly the same rate. The amount of head-bobbing shown by the females, however, was dramatically different for each cage. In addition, the relative amount of head-bobbing for the males and females in each cage was different. It is unlikely that the differences have anything to do with rearing or environment, so perhaps the behavior serves some other purpose aside from or in addition to courtship, or is just more of a personality trait, particularly for the females where the frequency of the behavior is so dramatically varied from one to the next.
Proximity scans are interesting because birds in the flight cage, containing more birds, but also having more available space per bird than any other cage, spent so much more time proximate to other birds compared to any of the other cages (Figure 2). Even the released birds, of which there were only five and which had an infinite number of places they could be, still chose to spend nearly 20% of their time proximate to other birds. Large group cages such as the flight cage also seemed to help bring out flocking behavior in the birds, once a characteristic of wild Bali mynahs.
Flocks for juvenile birds, also once a characteristic of wild Bali mynah populations, may also play a role in helping to reduce feather loss in captive birds. The present enclosures of grown birds did not appear to play a role, being that birds sharing nearly identical facilities still showed very different amounts of the feather loss condition, and the primary difference that existed between birds with and without the condition must then have been a consequence of rearing. The most plausible difference in rearing conditions had to do with whether or not the birds would have been incorporated into a flock as juveniles. Birds at Begawan Giri were placed into a flight cage, and even birds reared under the relatively poor conditions at the TNBB were also placed in large groups at a young age, and almost none showed obvious feather loss. Birds whose origins were from other places such as England or the Netherlands, where large scale breeding would not occur and juvenile flocks were less likely, more frequently exhibited feather loss.
Figure 2. This graph shows the average percent of scans that the birds were within 1.5 feet of another bird. The D27 pair spent less time proximate to each other compared to any other cage (t=9.59, df=74, p=.000). The flight cage birds spent more time proximate to other birds than the birds of any other cage (t=2.43, df=41, p=.019). Released birds spent significantly more time proximate to other birds than the D27 pair, and significantly less time than all other groups (t=4.56, df=53, p=.000; t=2.84, df=54, p=.006).
Figure 4. This graph shows the average number of allogrooming bouts initiated by males and females from each cage per hour. Females initiated allogrooming behaviors more than males (t=4.74, df=114, p=.000), and Cage D27 birds initiated significantly fewer bouts than Cage 4 and 16 birds (t=5.24, df=114, p=.000), which were not significantly different from each other (t=1.90, df=76, p=.061).