Cultural transmission, the social learning of information or behaviors from conspecifics 1–5, is believed to occur in a number of groups of animals, including primates 1, 6–9, cetaceans 4, 10, 11, ...and birds 3, 12, 13. Cultural traits can be passed vertically (from parents to offspring), obliquely (from the previous generation via a nonparent model to younger individuals), or horizontally (between unrelated individuals from similar age classes or within generations) 4. Male humpback whales (Megaptera novaeangliae) have a highly stereotyped, repetitive, and progressively evolving vocal sexual display or “song” 14–17 that functions in sexual selection (through mate attraction and/or male social sorting) 18–20. All males within a population conform to the current version of the display (song type), and similarities may exist among the songs of populations within an ocean basin 16, 17, 21. Here we present a striking pattern of horizontal transmission: multiple song types spread rapidly and repeatedly in a unidirectional manner, like cultural ripples, eastward through the populations in the western and central South Pacific over an 11-year period. This is the first documentation of a repeated, dynamic cultural change occurring across multiple populations at such a large geographic scale.
► Humpback whale songs have repeatedly moved east across the South Pacific ► The songs moved across the region in a series of cultural waves ► The waves frequently caused complete “cultural revolution” of the song ► The scale, rate, and repetition of these cultural changes are unparalleled
Since June, 2018, the Gravity Recovery and Climate Experiment Follow‐On (GRACE‐FO) is extending the 15‐year monthly mass change record of the GRACE mission, which ended in June 2017. The GRACE‐FO ...instrument and flight system performance has improved over GRACE. Better attitude solutions and enhanced pointing performance result in reduced fuel consumption and gravity range rate post‐fit residuals. One accelerometer requires additional calibrations due to unexpected measurement noise. The GRACE‐FO gravity and mass change fields from June 2018 through December 2019 continue the GRACE record at an equivalent precision and spatiotemporal sampling. During this period, GRACE‐FO observed large interannual terrestrial water variations associated with excess rainfall (Central US, Middle East), drought (Europe, Australia), and ice melt (Greenland). These observations are consistent with independent mass change estimates, providing high confidence that no intermission biases exist from GRACE to GRACE‐FO, despite the 11‐month gap. GRACE‐FO has also successfully demonstrated satellite‐to‐satellite laser ranging interferometry.
Plain Language Summary
Mass change is a fundamental climate system indicator and provides an integrated global view of how Earth's water cycle and energy balance are evolving. The Gravity Recovery and Climate Experiment (GRACE) mission monitored mass changes every month from 2002 through 2017. Since June 2018, GRACE Follow‐On (GRACE‐FO) continues this data record, tracking and monitoring changes in ice sheets and glaciers, near‐surface and underground water storage, as well as changes in sea level and ocean currents. GRACE‐FO instruments have been successfully calibrated and are providing new monthly mass change observations at a consistent spatial resolution and data quality with GRACE. Since its launch, GRACE‐FO has measured record land water storage changes in 2018 and 2019 in response to extreme heat waves and droughts over Europe and Australia, as well as to extreme rainfall events over the United States and Middle East. In the summer of 2019, GRACE‐FO measured record‐level Greenland mass loss rates. A novel laser ranging interferometer was successfully demonstrated on GRACE‐FO, laying the groundwork for improved future satellite gravity observations.
Key Points
GRACE‐FO is extending the 15‐year GRACE record of global monthly mass change at an equivalent precision and spatiotemporal sampling
Since its launch in 2018, GRACE‐FO has observed large water storage and ice mass changes driven by interannual climate anomalies
GRACE‐FO's instrument/flight system performance has largely improved over GRACE. The novel laser ranging instrument works successfully
Cultural processes occur in a wide variety of animal taxa, from insects to cetaceans. The songs of humpback whales are one of the most striking examples of the transmission of a cultural trait and ...social learning in any nonhuman animal. To understand how songs are learned, we investigate rare cases of song hybridization, where parts of an existing song are spliced with a new one, likely before an individual totally adopts the new song. Song unit sequences were extracted from over 9,300 phrases recorded during two song revolutions across the South Pacific Ocean, allowing fine-scale analysis of composition and sequencing. In hybrid songs the current and new songs were spliced together in two specific ways: (i) singers placed a single hybrid phrase, in which content from both songs were combined, between the two song types when transitioning from one to the other, and/or (ii) singers spliced complete themes from the revolutionary song into the current song. Sequence analysis indicated that both processes were governed by structural similarity rules. Hybrid phrases or theme substitutions occurred at points in the songs where both songs contained “similar sounds arranged in a similar pattern.” Songs appear to be learned as segments (themes/phrase types), akin to birdsong and human language acquisition, and these can be combined in predictable ways if the underlying structural pattern is similar. These snapshots of song change provide insights into the mechanisms underlying song learning in humpback whales, and comparative perspectives on the evolution of human language and culture.
In the context of a changing climate, understanding the environmental drivers of marine megafauna distribution is important for conservation success. The extent of humpback whale breeding habitats ...and the impact of temperature variation on their availability are both unknown. We used 19 years of dedicated survey data from seven countries and territories of Oceania (1,376 survey days), to investigate humpback whale breeding habitat diversity and adaptability to climate change. At a fine scale (1 km resolution), seabed topography was identified as an important influence on humpback whale distribution. The shallowest waters close to shore or in lagoons were favored, although humpback whales also showed flexible habitat use patterns with respect to shallow offshore features such as seamounts. At a coarse scale (1° resolution), humpback whale breeding habitats in Oceania spanned a thermal range of 22.3–27.8°C in August, with interannual variation up to 2.0°C. Within this range, both fine and coarse scale analyses of humpback whale distribution suggested local responses to temperature. Notably, the most detailed dataset was available from New Caledonia (774 survey days, 1996–2017), where encounter rates showed a negative relationship to sea surface temperature, but were not related to the El Niño Southern Oscillation or the Antarctic Oscillation from previous summer, a proxy for feeding conditions that may impact breeding patterns. Many breeding sites that are currently occupied are predicted to become unsuitably warm for this species (>28°C) by the end of the 21st century. Based on modeled ecological relationships, there are suitable habitats for relocation in archipelagos and seamounts of southern Oceania. Although distribution shifts might be restrained by philopatry, the apparent plasticity of humpback whale habitat use patterns and the extent of suitable habitats support an adaptive capacity to ocean warming in Oceania breeding grounds.
Cultural transmission of behaviour is important in a wide variety of vertebrate taxa from birds to humans. Vocal traditions and vocal learning provide a strong foundation for studying culture and its ...transmission in both humans and cetaceans. Male humpback whales (
Megaptera novaeangliae
) perform complex, culturally transmitted song displays that can change both evolutionarily (through accumulations of small changes) or revolutionarily (where a population rapidly adopts a novel song). The degree of coordination and conformity underlying song revolutions makes their study of particular interest. Acoustic contact on migratory routes may provide a mechanism for cultural revolutions of song, yet these areas of contact remain uncertain. Here, we compared songs recorded from the Kermadec Islands, a recently discovered migratory stopover, to multiple South Pacific wintering grounds. Similarities in song themes from the Kermadec Islands and multiple wintering locations (from New Caledonia across to the Cook Islands) suggest a location allowing cultural transmission of song eastward across the South Pacific, active song learning (hybrid songs) and the potential for cultural convergence after acoustic isolation at the wintering grounds. As with the correlations in humans between genes, communication and migration, the migration patterns of humpback whales are written into their songs.
Humpback whales have a continually evolving vocal sexual display, or "song," that appears to undergo both evolutionary and "revolutionary" change. All males within a population adhere to the current ...content and arrangement of the song. Populations within an ocean basin share similarities in their songs; this sharing is complex as multiple variations of the song (song types) may be present within a region at any one time. To quantitatively investigate the similarity of song types, songs were compared at both the individual singer and population level using the Levenshtein distance technique and cluster analysis. The highly stereotyped sequences of themes from the songs of 211 individuals from populations within the western and central South Pacific region from 1998 through 2008 were grouped together based on the percentage of song similarity, and compared to qualitatively assigned song types. The analysis produced clusters of highly similar songs that agreed with previous qualitative assignments. Each cluster contained songs from multiple populations and years, confirming the eastward spread of song types and their progressive evolution through the study region. Quantifying song similarity and exchange will assist in understanding broader song dynamics and contribute to the use of vocal displays as population identifiers.
Cultural transmission of behaviour is an important aspect of many animal communities ranging from humans to birds. Male humpback whales (
) sing a repetitive, stereotyped, socially learnt and ...culturally transmitted song display that slowly evolves each year. Most males within a population sing the same, slow-evolving song type; but in the South Pacific, song 'revolutions' have led to rapid and complete replacement of one song type by another introduced from a neighbouring population. Songs spread eastwards, from eastern Australia to French Polynesia, but the easterly extent of this transmission was unknown. Here, we investigated whether song revolutions continue to spread from the central (French Polynesia) into the eastern (Ecuador) South Pacific region. Similarity analyses using three consecutive years of song data (2016-2018) revealed that song themes recorded in 2016-2018 French Polynesian song matched song themes sung in 2018 Ecuadorian song, suggesting continued easterly transmission of song to Ecuador, and vocal connectivity across the entire South Pacific Ocean basin. This study demonstrates songs first identified in western populations can be transmitted across the entire South Pacific, supporting the potential for a circumpolar Southern Hemisphere cultural transmission of song and a vocal culture rivalled in its extent only by our own.
For cetaceans, population structure is traditionally determined by molecular genetics or photographically identified individuals. Acoustic data, however, has provided information on movement and ...population structure with less effort and cost than traditional methods in an array of taxa. Male humpback whales (Megaptera novaeangliae) produce a continually evolving vocal sexual display, or song, that is similar among all males in a population. The rapid cultural transmission (the transfer of information or behavior between conspecifics through social learning) of different versions of this display between distinct but interconnected populations in the western and central South Pacific region presents a unique way to investigate population structure based on the movement dynamics of a song (acoustic) display. Using 11 years of data, we investigated an acoustically based population structure for the region by comparing stereotyped song sequences among populations and years. We used the Levenshtein distance technique to group previously defined populations into (vocally based) clusters based on the overall similarity of their song display in space and time. We identified the following distinct vocal clusters: western cluster, 1 population off eastern Australia; central cluster, populations around New Caledonia, Tonga, and American Samoa; and eastern region, either a single cluster or 2 clusters, one around the Cook Islands and the other off French Polynesia. These results are consistent with the hypothesis that each breeding aggregation represents a distinct population (each occupied a single, terminal node) in a metapopulation, similar to the current understanding of population structure based on genetic and photo‐identification studies. However, the central vocal cluster had higher levels of song‐sharing among populations than the other clusters, indicating that levels of vocal connectivity varied within the region. Our results demonstrate the utility and value of using culturally transmitted vocal patterns as a way of defining connectivity to infer population structure. We suggest vocal patterns be incorporated by the International Whaling Commission in conjunction with traditional methods in the assessment of structure.
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