Red Shift, Blue Shift: Investigating Doppler Shifts, Blubber Thickness, and Migration as Explanations of Seasonal Variation in the Tonality of Antarctic Blue Whale Song

Abstract

The song of Antarctic blue whales (Balaenoptera musculus intermedia) comprises repeated, stereotyped, low-frequency calls. Measurements of these calls from recordings spanning many years have revealed a long-term linear decline as well as an intra-annual pattern in tonal frequency. While a number of hypotheses for this long-term decline have been investigated, including changes in population structure, changes in the physical environment, and changes in the behaviour of the whales, there have been relatively few attempts to explain the intra-annual pattern. An additional hypothesis that has not yet been investigated is that differences in the observed frequency from each call are due to the Doppler effect. The assumptions and implications of the Doppler effect on whale song are investigated using 1) vessel-based acoustic recordings of Antarctic blue whales with simultaneous observation of whale movement and 2) long-term acoustic recordings from both the subtropics and Antarctic. Results from vessel-based recordings of Antarctic blue whales indicate that variation in peak-frequency between calls produced by an individual whale was greater than would be expected by the movement of the whale alone. Furthermore, analysis of intra-annual frequency shift at Antarctic recording stations indicates that the Doppler effect is unlikely to fully explain the observations of intra-annual pattern in the frequency of Antarctic blue whale song. However, data do show cyclical changes in frequency in conjunction with season, thus suggesting that there might be a relationship among tonal frequency, body condition, and migration to and from Antarctic feeding grounds.

Long‐Term and Seasonal Changes of Large Whale Call Frequency in the Southern Indian Ocean

“…As mentioned in section 1, there is no satisfactory explanation for this seasonal frequency change (Gavrilov et al, ; Miller et al, ), other than that it may have a different cause from the long‐term decline. Here we notice that the ambient noise, especially in the 10‐ to 13‐Hz and 30‐ to 33‐Hz frequency bands, displays seasonal variations, similar to the frequency variations seen in blue whale Z‐calls (Figures a and b).…”

“…The consistency of the observed seasonal shifts at six distant sites, based on more than a million samples, covering six continuous years (Figure ), suggests that the frequency changes over time are not measurement artifacts; the largest dispersion occurs in the austral late spring and summer, when the Antarctic blue whale presence is the lowest at the site latitudes. In addition, different approaches provided independent evidence for this seasonal shift (Gavrilov et al, ; Miller et al, ).…”

Seasonal and Diel Vocalization Patterns of Antarctic Blue Whale (Balaenoptera musculus intermedia) in the Southern Indian Ocean: A Multi-Year and Multi-Site Study

“…The frequency parameters U and L are adapted depending on the year of the treated recordings. Indeed, the frequency of the unit A of Z-calls appears to be decreasing in the past decades [17–20], at an estimated rate of 0.135 Hz per year [19]. The Z-detector is robust to frequency variations between calls and to intra-annual changes, but to ensure this flexibility while limiting the number of false detections, the frequency interval into which the model can vary is limited to 0.5 Hz.…”

“…Z-calls are constituted of three parts: a tonal unit A, lasting about 7 to 12 s at a frequency near 28 Hz [6, 15, 16], a short downsweep of 1 to 2 s, and a tonal unit B, lasting between 7 and 12 s, at a frequency around 18 Hz. Frequency of unit A appears to be decreasing in the past decades [17–20]. Z-calls are repeated in sequences, every 40 to 70 s during several minutes to hours [6, 10, 15, 21, 22].…”

Copper-paracetamol complexes: Promising lead antibacterial drug candidates

“…There was a blue shift when DMSO quenched the absorption of the reaction products at other wavelengths except 260 nm. Absorption within the visible range is directly affected by DMSO and results in a red shift (a shift in frequency towards lower energy or longer wavelength) and a blue shift (shift in the frequency towards a higher energy or a shorter wavelength) (Diana et al, 2012;Miller et al, 2014). It is therefore indicative from the results that, there was a blue shift in the sample 1, sample 2 and yellow extract.…”