Age-Related Testosterone Changes and Corresponding Song Patterns in Red-whiskered Bulbul (Pycnonotus jocosus Linnaeus, 1758)

Abstract

We monitored total testosterone profiles and song patterns of 12 males and 2 females Red-whiskered Bulbuls (Pycnonotus jocosus), aged 5-10 months. Each bird was maintained in a cage sized of 38 × 38 × 50 cm and raised in a 22 °C-controlled room-sized of 6 × 10 × 3.5 m. The song prototype was played during 0700-11.00 h, with an amplifier-connected loudspeaker placed at the center and the song was recorded during both 1100-1200 and 1300-1500 h, and then their sonograms were analyzed with Avisoft SAS Lab Pro, version 4.3. Feces were collected monthly and immediately following recording their songs to determine male and female total testosterone levels by radioimmunoassay. The results demonstrated that an average of a frequency that the male and the female birds produced was 4.27 ± 0.13 kHz with a frequency range of 1.50 - 5.18 kHz. The males aged 8-10 months old produced songs with an average of 25.83 syllables/10 s, similar to those found in the song prototype while the females produced those with an average of 18.33 syllables/10 s. The males produced songs consisting of more syllables and fewer intervals than those of the females. The coefficient of correlations between the mean total testosterone levels with the syllables/10 s and intervals/10 s were +0.68 and -0.69, respectively. Additionally, the male Red-whiskered Bulbuls created the complicated and various song types that corresponded well with the marked increases in the total testosterone levels at the age of 8 to 10 months old.