Miksis-Olds Jennifer L, Nieukirk Sharon L, Harris Danielle V
School of Marine Science and Ocean Engineering, University of New Hampshire, 24 Colovos Road, Durham, New Hampshire 03824, USA.
Oregon State University and NOAA Pacific Marine Environmental Laboratory, Hatfield Marine Science Center, 2030 South East Marine Science Drive, Newport, Oregon 97365, USA.
J Acoust Soc Am. 2018 Dec;144(6):3618. doi: 10.1121/1.5084269.
Sri Lankan pygmy blue whale song consists of three repeated units: (1) low frequency pulsive unit, (2) frequency modulated (FM) upsweep, and (3) long tonal downsweep. The Unit 2 FM unit has up to three visible upsweeps with energy concentrated at approximately 40, 50, and 60 Hz, while the Unit 3 (∼100 Hz) tonal downsweep is the most distinct unit lasting 20-30 s. Spectral characteristics of the Units 2 and 3 song elements, along with ocean sound levels, were analyzed in the Indian Ocean from 2002 to 2013. The peak frequency of the tonal Unit 3 calls decreased from approximately 106.5 to 100.7 Hz over a decade corresponding to a 5.4% decrease. Over the same time period, the frequency content of the Unit 2 upsweeps did not change as dramatically with only a 3.1% change. Ambient sound levels in the vocalization bands did not exhibit equivalent patterns in amplitude trends. Analysis showed no increase in the ambient sound or compensated peak amplitude levels of the tonal downsweeps, eliminating the presence of a Lombard effect. Here it is proposed that each song unit may convey different information and thus may be responding to different selective pressures.
（1）低频脉冲单元，（2）调频（FM）上升扫描，以及（3）长音调下降扫描。单元2的调频单元有多达三个可见的上升扫描，能量集中在约40、50和60赫兹，而单元3（约100赫兹）的音调下降扫描是最明显的单元，持续20 - 30秒。2002年至2013年期间，在印度洋对单元2和单元3歌声元素的频谱特征以及海洋声级进行了分析。在十年间，音调单元3叫声的峰值频率从约106.5赫兹降至100.7赫兹，降幅为5.4%。在同一时期，单元2上升扫描的频率内容变化没有那么显著，仅变化了3.1%。发声频段的环境声级在振幅趋势上没有呈现出相同的模式。分析表明，环境声或音调下降扫描的补偿峰值振幅水平没有增加，排除了伦巴德效应的存在。在此提出，每个歌声单元可能传达不同的信息，因此可能对不同的选择压力做出反应。
