How Do Scientists Determine Whether Humpback Whale Songs Change From One Breeding Season to the Next in Samaná Bay?

Humpback whales produce some of the most complex vocal displays in the ocean. Their songs contain repeated sound units arranged into phrases and longer sequences, creating patterns that scientists can record and compare over time.

In the waters around Samaná Bay in the Dominican Republic, humpback whales are a major focus of seasonal wildlife observation. Long-term acoustic monitoring could help researchers investigate whether songs recorded during one breeding season differ from those recorded in another.

But detecting a difference is only the beginning. Scientists must determine whether the change reflects genuine variation in whale song, differences among individual singers, changes in recording equipment, or limitations in the available samples.

This guide explains how researchers compare humpback whale songs between breeding seasons, which acoustic features they examine, and why careful interpretation matters.

What Does It Mean for a Humpback Whale Song to Change?

A humpback whale song is not simply one sound repeated indefinitely. It can contain distinct units, phrases, and sequences organized into a broader structure.

Changes can occur at several levels:

Sound units: Individual vocal elements may differ in their frequency contours, duration, or other acoustic features.
Phrases: The order or composition of repeated sound units may change.
Song structure: Larger sequences may contain different arrangements of phrases.
Timing: The pauses between units or phrases may vary.
Song prevalence: Certain patterns may occur more often in one recording period than another.

These differences are not all equivalent. A whale may produce the same general song pattern with small variations in individual sounds, while a more substantial change may involve the addition, removal, or rearrangement of song elements.

Scientists therefore define what they mean by a song change before comparing recordings. This makes it easier to distinguish meaningful patterns from ordinary variation.

1. Collecting Recordings Across Multiple Breeding Seasons

The first requirement is a set of usable recordings from different seasons.

Researchers may deploy stationary hydrophones, record from research vessels, or use a combination of acoustic monitoring methods. Each recording session should include information about the date, location, equipment, recording settings, and environmental conditions.

For a potential study in Samaná Bay, a monitoring program could collect recordings during comparable periods of successive breeding seasons. Matching the observation periods helps reduce the risk of confusing seasonal timing with differences between years.

For example, comparing recordings collected during an early-season period in one year with late-season recordings from another may produce differences that are partly related to the stage of the season.

Researchers should also document gaps in monitoring. A year with only a few hours of usable audio cannot necessarily be compared fairly with a year containing continuous recordings.

Long-term consistency is essential because the purpose is to identify changes in whale songs rather than changes in how the recordings were collected.

2. Identifying Song Units and Phrases

Before researchers can compare songs, they need to identify the acoustic components within each recording.

Analysts commonly examine spectrograms, which display how the frequencies in a sound change over time. These visual representations can help reveal repeated units, tonal contours, pauses, and sequences.

Researchers may divide a song into smaller components using clearly defined classification rules. Depending on the project, these components might be labeled by their frequency contour, duration, shape, or position within a phrase.

For example, an analyst might identify a recurring sound unit that rises in frequency before descending. The analyst can then compare its appearance and acoustic measurements with similar units from recordings collected in another year.

However, similar-looking sounds are not automatically identical units, and different-looking examples may reflect natural variation within the same general category.

A reliable study uses consistent definitions and checks ambiguous classifications rather than assuming every difference represents a new song element.

3. Comparing Frequency Contours and Sound Duration

Two recordings may contain similar song structures but differ in the acoustic characteristics of individual units.

Scientists can measure features such as:

Starting and ending frequency.
Highest and lowest frequency.
Duration of each unit.
Direction and shape of frequency changes.
Distribution of acoustic energy.
Timing between repeated units.

These measurements can help determine whether a sound pattern has changed between recording periods.

For example, researchers might find that a particular category of sound tends to last longer in one dataset than in another. They would then need to investigate whether the difference is consistent, large enough to matter, and robust to recording conditions.

Microphone sensitivity, sample rate, background noise, and analysis settings can influence the measurements. Scientists must account for these factors before attributing an acoustic difference to the whales.

Frequency and duration measurements are useful indicators, but neither one alone establishes that the overall song has changed.

4. Comparing the Sequence of Song Elements

A song's organization can be as informative as its individual sounds.

Researchers can examine whether phrases occur in a similar order, whether certain units repeatedly appear together, and whether the sequence of phrases differs across recording periods.

One approach is to create a sequence of labeled units for each song and compare the order of those labels. This allows analysts to investigate whether songs share the same general structure or contain different arrangements.

For instance, two recordings may contain many of the same sound units, but one may show a different phrase sequence. Another recording may contain a new unit or lack a previously common element.

Scientists should distinguish between a genuinely different sequence and a recording that captured only part of a song. An incomplete recording can make a familiar song appear structurally different.

A comparison is more reliable when the available recordings are long enough to capture the relevant sequence and when the same classification procedures are applied to both datasets.

5. Using Acoustic Software to Compare Songs

Large acoustic datasets can be difficult to compare manually. Researchers may use audio-analysis software to visualize sound patterns, measure acoustic features, and organize recordings into comparable categories.

Depending on the research question, methods may include:

Spectrogram inspection.
Acoustic feature extraction.
Similarity measurements between sound units.
Sequence-alignment techniques.
Clustering of acoustically similar sounds.
Machine-learning tools for classifying vocalizations.

These methods can help scientists identify patterns that would be difficult to detect consistently by listening alone.

However, automated similarity does not necessarily equal biological similarity. A model may classify two sounds as different because of recording noise or as similar because they share broad acoustic features.

Researchers should validate automated results against representative recordings, check uncertain classifications, and document the analysis settings.

The best method depends on the type of change being investigated. Comparing individual sound units requires a different approach from comparing entire song sequences.

6. Separating Song Changes From Recording Differences

A major challenge in multi-year research is ensuring that differences between recordings are not caused by changes in the measurement process.

Suppose a study uses one hydrophone in the first year and a different model in the next. If the equipment has different frequency sensitivity, the resulting recordings may not be directly comparable without appropriate calibration or correction.

7. Distinguishing Changes Within Songs From Changes Between Whales

Not every difference between recordings means that the same whales have changed their songs.

One season may include a different mixture of singers from another season. If different individuals produce different song patterns, the overall dataset can change even when individual whales have not changed their own vocal behavior.

To investigate this problem, researchers may combine acoustic recordings with photo-identification, visual observations, or other evidence that helps characterize the animals present.

When the same individual can be linked reliably to recordings collected at different times, scientists may be able to investigate changes in that individual's vocal patterns more directly.

However, linking a specific song to an individual whale can be difficult, particularly when several whales are vocalizing within the same area.

Without evidence identifying the singers, researchers should be cautious about claiming that a particular whale changed its song. They may instead report that the recorded song patterns differed between sampling periods.

8. Understanding Song Changes and Cultural Transmission

Humpback whale songs have attracted scientific interest partly because song patterns can change and spread among singers.

In some studied humpback whale populations, researchers have documented substantial changes in song patterns over time, including changes consistent with cultural transmission between groups.

This broader research provides a reason to compare songs across years. Scientists can investigate whether particular units or sequences persist, disappear, or become more common.

Nevertheless, not every acoustic difference demonstrates cultural transmission. A new pattern in a recording could reflect an unfamiliar singer, a previously undetected variation, or differences in sampling.

To investigate how a song pattern spreads, researchers need more than evidence that it changed. They also need information about the timing and distribution of the pattern and, where possible, the relationships among the whales or groups involved.

A study in Samaná Bay would need appropriate local data before drawing conclusions about how song patterns change or spread in that region.

9. Comparing Multiple Years Instead of Only Two Seasons

Comparing two breeding seasons can reveal a difference, but additional years help scientists determine whether the pattern persists.

A song feature might appear in one year and disappear in the next. It could also become progressively more common over several years or fluctuate without a clear long-term trend.

Researchers can investigate these possibilities by organizing recordings into a multi-year dataset and tracking the occurrence of defined acoustic features.

For example, a study could measure the proportion of analyzed song sequences containing a particular unit in each season. The results could show whether the unit remains common, becomes less frequent, or appears only during certain periods.

The interpretation depends on the quality and representativeness of the recordings. A pattern that appears absent from one year's dataset may simply have been missed because of limited sampling.

Multi-year monitoring provides stronger context than a single comparison, but it does not remove every source of uncertainty.

10. Measuring Uncertainty in Song Comparisons

Scientists should evaluate how confident they can be that an observed difference is meaningful.

Some song units may be difficult to classify, while others may be obscured by vessel noise or overlapping vocalizations. A recording may also be too short to establish the complete structure of a song.

Researchers can address these problems by reviewing uncertain samples, applying consistent classification criteria, and reporting the limitations of their data.

Statistical analysis may help determine whether observed differences are larger or more consistent than expected from ordinary variation. The appropriate method depends on the dataset and the specific acoustic features being compared.

Results should include information about sample sizes, recording coverage, and uncertainty wherever possible.

An honest report may conclude that the evidence is insufficient to determine whether a song has changed. Such a conclusion is scientifically valuable because it identifies what additional monitoring is needed.

11. Why Song Changes Matter for Whale Research

Studying changes in humpback whale songs can contribute to a broader understanding of communication, behavior, and population-level patterns.

Researchers may investigate whether song elements persist across years, whether particular patterns appear in different locations, or whether changes coincide with shifts in the composition of the observed whales.

Acoustic data can also support long-term monitoring when visual observations are limited. Underwater recordings may capture vocal activity even when whales are not visible at the surface.

However, song changes should not be treated as direct measurements of whale abundance, reproductive success, or population health. Those questions require additional evidence and suitable research designs.

For conservation planning, the value of acoustic monitoring comes from combining reliable sound analysis with other observations rather than relying on song patterns alone.

12. What Researchers Could Investigate in Samaná Bay

A long-term acoustic study in Samaná Bay could compare song units and phrase sequences across successive breeding seasons.

Researchers could ask several focused questions:

Which song units recur across multiple seasons?
Do the frequency contours or durations of selected units change?
Does the sequence of phrases remain similar from year to year?
Are some patterns detected in one period but not another?
Can observed differences be explained by changes in the singers or recording conditions?

Answering these questions would require a consistent monitoring program, clear acoustic classification methods, and recordings that represent the periods being compared.

Researchers could also compare local results with suitable reference datasets from other regions, provided that differences in equipment, sampling, and analysis are taken into account.

These are research possibilities, not claims that a particular song change has already been documented in Samaná Bay. Region-specific findings must be supported by verified local evidence.

Conclusion

Scientists investigate changes in humpback whale songs between breeding seasons by collecting comparable recordings, identifying song units and phrases, measuring acoustic features, and examining how song sequences are organized.

Reliable comparisons require researchers to account for recording equipment, background noise, incomplete samples, and differences among individual singers. Multi-year datasets can help reveal whether patterns persist, disappear, or change over time.

For Samaná Bay, long-term acoustic monitoring could provide valuable information about humpback whale communication. The strongest conclusions will come from consistent methods, transparent reporting, and careful separation of measured differences from explanations that require further evidence.

Frequently Asked Questions

Do humpback whale songs change every year?

Song patterns can change over time, but the extent and timing of changes vary. Researchers need recordings from comparable periods to determine what changed in a particular population or location.

How do scientists compare whale songs from different years?

They analyze acoustic recordings, identify song units and phrases, compare frequency and duration measurements, and examine the sequence of song elements using consistent methods.

Can scientists prove that the same whale changed its song?

Only when the available evidence supports linking recordings to the same individual. Otherwise, differences may reflect changes in which whales were recorded.

What is the role of spectrograms in studying song changes?

Spectrograms help scientists visualize sound frequencies over time. They make it easier to compare contours, repeated units, and phrase structure across recordings.

Does a different song mean a new whale population is present?

Not necessarily. Song differences can have multiple explanations. Researchers need independent evidence before drawing conclusions about population identity or movement.

Have scientists documented specific annual song changes in Samaná Bay?

Any claim about a particular change in Samaná Bay should be supported by verified local recordings or published research. General knowledge about humpback whale song evolution does not establish a specific local trend.

How Humpback Whale Songs Change Between Seasons