A Preliminary Study On The Change Mechanism Of Plumage In Breeding Period

From December,2013 to July,2014 and December,2014 to February,2015, the process of plumage color change of the Crested Ibis (Nipponia nippon) in capativity during the breeding season was observed in Reintroduction Base of the Crested Ibis in Ningshan County of Shaanxi province. We chose 15 healthy and one foot-disabled caged individuals as the target samples. Instantaneous scanning sampling and focal sampling methods were used to collect data on the bathing and daubing behaviour, as well as on the plumage color changes. At the same time, the concentrations of the fecal steroid including testosterone, progesterone and estradiol, in which the feces was collected from two breeding pairs ( ♂ 329x♀ 714 and ♂ 315x♀739), were analyzed with enzyme-linked immunosorbent assay (ELISA) method. Microstructures of the skin in parts of particular area on neck was examined using paraffin sections to explore the source of the special black substance resulting in the plumage coloring. We aimed to detect the physiological mechanisms in color change by examining the microstructure of the neck skin and the relationship between the special behavior of bathing and daubing and concentrations of the fecal steroid. By understanding the process of the changes of plumage color, we can predict the start time of breeding season to take concervation measures for improving the reproductive success. The main results of our study are listed as follows.1. The diurnal activity time span in the breeding season of the caged Crested Ibis averaged at 14.27 ±1.04h, in which the resting behavior makes the maximum percentage (48.91%), then followed by foraging (20.36%), breeding (13.48%), movements (8.08%), preening (7.69%) and other behavior (1.48%). While the preening behavior consist of general (6.78%) and special preening (0.91%).2. The caged Crested Ibis present an unobvious rhythm of diurnal activity during the breeding season. A short feeding peak occur at 6:00-7:00, then followed by a slight fluctuation, gradual increase after 11:00, and reach a peak at 17:00-18:00. The reproductive behavior with lower proportion occurs more frequenly in the morning. Regardless of frequently, the preening account for a relatively low proportion and the fluctuation is unobvious.3. The bathing and daubing behavior was observed as soon as early in December. Plumage coloring was approximately at 70% by the end of January and was accomplished in March, while the special behavior last in the breeding season until June to maintain the grey plumage. The special behavior usually occurs at 13:00-17:00 every day, occasionally in the morning in a warm day. The bathing last at 7.00±2.69 min, and the daubing behavior including inside-post-bathing persist at 30.00±8.61min. The reason of why the ibises stay in a fixed area when bathing remains unknown.4. Pearson correlation analysis showed that the presence of bathing and daubing behavior of the females correlated significantly with the estradiol level (Pearson r= 0.823, P= 0.006< 0.01), and negative significanly correlated with the testosterone levels of the males (Pearson r= 0.692, P= 0.692< 0.05), whereas with no correlations with the level of progesterone. The presence of the special behavior of the male was not significantly associated with the levels of testosterone, but significantly correlated with of the level of estradiol (Pearson r= 0.934, P= 0.934< 0.01).5. Microstructures of the neck skin examined using paraffin sections indicated that there are some polygonal melanocyte-like cells underneath the epidermis. The physical trait, chemical character and structure of the black substance secreted by the neck skin has not been examined due to difficult sample collection. Hence, the mechanism of the production and secretion of the black substance is still unclear. Our results showed that the black substance is a kind of powdered instead of sebaceous material which is a fat-soluble matrix (wax, oil) that contained melanin. Therefore, we speculate that there may be wax gland in the neck skin where the black substance immersed into the feathers through matrix secreted by wax gland, and was extended to head, neck and back by emulsification in bathing.