Tess Gridley

University of Cape Town/ University of Stellenbosch

A signature whistle type is a learned, individually distinctive whistle type in a dolphin's acoustic repertoire that broadcasts the identity of the whistle owner. The acquisition and use of signature whistles indicates complex cognitive functioning that requires wider investigation in wild dolphin populations. Here we identify signature whistle typ...

The costs of predation may exert significant pressure on the mode of communication used by an animal, and many species balance the benefits of communication (e.g. mate attraction) against the potential risk of predation. Four groups of toothed whales have independently evolved narrowband high-frequency (NBHF) echolocation signals. These signals hel...

Robust abundance estimates of wild animal populations are needed to inform management policies and are often obtained through mark-recapture (MR) studies. Visual methods are commonly used, which limits data collection to daylight hours and good weather conditions. Passive acoustic monitoring offers an alternative, particularly if acoustic cues are...

Egyptian Geese Alopochen aegyptiaca are distributed across most of Africa. Their calls dominate the soundscape of many urban areas, yet their acoustic behaviour is poorly documented or understood. Using acoustic recordings made across a range of behavioural contexts, groups sizes and compositions, we identified a repertoire of eight distinct call t...

We use genomics to identify the natal origin of a grey whale found in the South Atlantic, at least 20 000 km from the species core range (halfway around the world). The data indicate an origin in the North Pacific, possibly from the endangered western North Pacific population, thought to include only approximately 200 individuals. This contributes...

Mother-young vocal recognition is widespread in mammals. The features of vocal recognition are known to be shaped by the ecological constraints faced by each species. In some species, a rapid establishment of mother-young vocal recognition is crucial for offspring's survival. However, knowledge of the precise features of this recognition system, es...

Morphological abnormalities in wild animals can be indicators of the underlying health of a population and may be determined through routine photographic surveys. Here we assess unusual rostrum conditions in Indian Ocean humpback dolphins (Sousa plumbea) inhabiting South African coastal waters to understand the rate of prevalence of abnormal rostru...

In-air sounds of pinnipeds are important for interactions with conspecifics and threat displays. However, little is known about the in-air acoustic repertoire and associated behaviour of crabeater seals Lobodon carcinophaga. We investigated the in-air acoustic repertoire and associated behaviour of two male and one female wild juvenile crabeater se...

The Atlantic sector of the Southern Ocean (ASSO) has one of the highest densities of Antarctic krill ( Euphausia superba ) compared to other polar and subpolar regions, which attracts migratory baleen whale species to aggregate in this area for feeding. Humpback whales ( Megaptera novaeangliae ) also sing extensively while on the Southern Ocean fee...

Vocal recognition is widespread in the animal kingdom, and a necessary tool for offspring survival in some groups. Temporal patterns of animal vocalisations can facilitate communication and convey information such as identity, emotional state, or motivation of the caller. While pinniped (i.e., walrus, eared and true seals) vocalisations are general...

Abundance estimates of cetaceans are often acquired through capture‐recapture analysis of photographically identified individuals. An alternative method, using capture‐recapture of individually distinct signature whistles detected from acoustic underwater recording units, has recently been demonstrated. Here we investigate the effect of array confi...

The Cape fur seal (Arctocephalus pusillus pusillus) is one of the most colonial mammal species in the world. Females exclusively nurse their pups for 9 to 11 months, during which they alternate frequent foraging trips at sea with suckling periods ashore. The survival of the pup thus depends on the ability of the mother–pup pair to relocate each oth...

Details about the upcoming African Bioacoustics Community Conference

Humpback whales are a cosmopolitan, highly vocal species. Investigated here are their vocalizations recorded at the Vema Seamount (31°38′S, 08°20′E) from moored hydrophones in the austral spring of 2019. During the 11-d recording period over 600 non-song calls were detected. Calls were predominantly detected at night over three consecutive days. Th...

The increase of anthropogenic noise in the environment is a global phenomenon occurring in various types of habitats. Its impact on wildlife is therefore a growing research concern for many taxa. Due to their amphibious lifestyle, pinnipeds are exposed to anthropogenic noise in both aquatic and terrestrial environments. Using playback experiments,...

Sexing cetaceans typically requires extended periods of observation or expensive molecular methods. An alternative approach using photo‐identification may provide a cost‐effective, noninvasive method for assigning a sex to free‐ranging individuals. We investigated two methods for predicting the sex of common bottlenose dolphins (Tursiops truncatus)...

The cape fur seal is one of the most colonial mammal species in the world. Breeding colonies are composed of harems held by mature males (older than 10 years) with up to 30 females and their pups, while roaming subadult males (younger and socially immature) are kept away from bulls’ territories. As in other pinnipeds, cape fur seals are highly voca...

Bioacoustics has emerged as a useful method of data collection and analysis for diverse animals in a wide range of environments and has helped to describe, monitor, and conserve some of Africa’s species biodiversity. However, little is known about how much it contributes to the continent’s research corpus. We report results from a systematic review...

Passive acoustic monitoring (PAM) involves recording the sounds of animals and environments for research and conservation. PAM is used in a range of contexts across terrestrial, marine and freshwater environments. However, financial constraints limit applications within aquatic environments; these costs include the high cost of submersible acoustic...

Communication is fundamental for the survival of animal species as signals are involved in many social interactions (mate selection, parental care, collective behaviours). The acoustic channel is an important modality used by birds and mammals to reliably exchange information among individuals. In group-living species, the propagation of vocal sign...

Marine pollution is increasing, and pinnipeds are commonly affected by entanglement in waste. We investigated entanglement rates, common materials, and the demographic profile of Cape fur seals (Arctocephalus pusillus pusillus) affected at two Namibian colonies. Overall, we identified 366 cases of entanglement, and present a global rate of entangle...

Human-controlled regimes can entrain behavioural responses and may impact animal welfare. Therefore, understanding the influence of schedules on animal behaviour can be a valuable tool to improve welfare, however information on behaviour overnight and in the absence of husbandry staff remains rare. Bottlenose dolphins ( Tursiops spp.) are highly so...

The Indian Ocean humpback dolphin (Sousa plumbea) is "endangered" with likely less than 500 animals remaining in South African waters. Established in 2016, the SouSA Consortium is a formalised network of scientists and conservationists to combine knowledge and research efforts, and make coordinated decisions with the aim of conserving the species....

The ability to recognize the identity of conspecifics is a key component for survival of many animal species and is fundamental to social interactions such as parental care, intra-sexual competition or mate recognition. In group-living species, the simultaneous co-existence of many individuals increases the number of interactions and reinforces the...

Acoustical geographic variation is common in widely distributed species and it is already described for several taxa, at various scales. In cetaceans, intraspecific variation in acoustic repertoires has been linked to ecological factors, geographical barriers, and social processes. For the common bottlenose dolphin ( Tursiops truncatus ), studies o...

Defining the trophic relationships of marine predators and their dietary preferences is essential in understanding their role and importance in ecosystems. Here we used stable isotope analysis of skin samples (δ ¹⁵ N values reflecting trophic level and δ ¹³ C values reflecting foraging habitat) to investigate resource partitioning and spatial diffe...

Human-controlled regimes can entrain behavioural responses and may impact animal welfare. Therefore, understanding the impact of schedules on animal behaviour can be a valuable tool to improve welfare, however information on overnight behaviour and behaviour in the absence of husbandry staff remains rare. Bottlenose dolphins ( Tursiops spp.) are hi...

Dwarf sperm whales (Kogia sima) are small toothed whales that produce narrow-band high-frequency (NBHF) echolocation clicks. Such NBHF clicks, subject to high levels of acoustic absorption, are usually produced by small, shallow-diving odontocetes, such as porpoises, in keeping with their short-range echolocation and fast click rates. Here, we soug...

Whistlers of the waves NASA From the day they are born, dolphins produce high-pitched whistles. At first the whistle contours are quite varied and unclear, but within a few months calves develop an individually distinctive whistle contour, through learning and practice. These whistle contours are used by each dolphin when communicating with other d...

The genus Cephalorhynchus contains four dolphin species, of which three are classified as Near Threatened or Endangered and one subspecies is close to extinction. Understanding the species' abundance, distributions and habitat preferences is necessary for effective management to prevent further population declines. Heaviside's dolphin C. heavisidii...

Knowledge of a population's abundance is of primary importance for conservation management. However, robust estimates of abundance are often difficult to obtain, especially for cetaceans which spend most of their lives submerged. Cetacean abundance is commonly estimated using aerial or vessel-based line transect surveys and distance sampling method...

Humpback whales are known for their complex and well-structured song that is typically produced on low-latitude breeding grounds. However, there is increasing evidence of song production on migration routes and high-latitude feeding grounds. Within a breeding ground and season, males share songs that progressively change over time. Song production...

The Importance of Volunteer Funded Research amid current global challenges

In light of the global COVID-19 crisis, the ABC has decided to push forward with a hybrid conference, moving all presentations to an online space with the option of attending in-person at the University of Stellenbosch in South Africa if government restrictions allow. This conference will show-case the diverse field of bioacoustics and bring togeth...

Extended nursing periods have been observed in some pinniped species. Here, we document multiple cases of such prolonged nursing in Cape fur seals in Namibia. Over three separate visits to the Cape Cross breeding colony, we observed five unusual nursing interactions. These included animals of estimated age from one to over three years suckling on a...

The four currently recognised species of Sousa are all threatened on the IUCN Red List. To date they have not been included in any of the available software platforms that have been developed for the automated matching of cetaceans from photo-ID data. Because of their unique morphology, existing algorithms are unlikely to be successful and new algo...

Humpback whales (Megaptera novaeangliae) are highly vocal, producing a wide repertoire of sounds often organised into song. Song is prolific at breeding sites but also documented along migration routes and at feeding sites, including along the west coast of South Africa (28°–34°S). Here we examine the occurrence of humpback whale song within False...

Conveying identity is important for social animals to maintain individually based relationships. Communication of identity information relies on both signal encoding and perception. Several delphinid species use individually distinctive signature whistles to transmit identity information, best described for the common bottlenose dolphin (Tursiops t...

Humpback whale is known for the complex songs performed by the males to attract females, during the migration and mating season. The south western of Indian ocean is a breeding area from July to September for tis species. This is the first interregional acoustic study of this area which aim to better understand the cultural song transmission of hum...

Knowledge of the occurrence and distribution of cetaceans is particularly important for conservation and management, but is still limited within Namibian waters. We collated 3211 cetacean records from the Namibian Exclusive Economic Zone (EEZ) for the period 2008 to 2016 and applied the principle of minimum cross entropy (MinxEnt) to predict habita...

An infographic on humpback dolphins developed by Coen Soeteman as part of his undergraduate work in GeoMedia and Design through HAS University (Netherlands) under the supervision of S Elwen and T Gridley

The coastal population of common bottlenose dolphins Tursiops truncatus found in Namibia is regionally isolated and unique. This population faces several potential anthropogenic threats, especially in Walvis Bay, including boat-based tourism, a commercial harbour undergoing expansion, and aquaculture for oysters and mussels. Between 2008 and 2012,...

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Four groups of toothed whales have independently evolved to produce narrowband high-frequency (NBHF) echolocation signals (i.e. clicks) with a strikingly similar waveform and centroid frequency around 125 kHz. These signals are thought to help NBHF species avoid predation by echolocating and communicating at frequencies inaudible to predators, a fo...

Humpback whales (Megaptera novaeangliae) are a very vocal species, using a variety of sounds during their lifetime. It has recently been determined that these whales are not only present along the western coast of South Africa during two peaks (May - July and September - December) as they migrate to and from their breeding and feeding grounds, but...

The bottlenose dolphin, genus Tursiops is one of the best studied of all the Cetacea with a minimum of two species widely recognised. Common bottlenose dolphins (T. truncatus), are the cetacean species most frequently held in captivity and are known to hybridize with species from at least 6 different genera. In this study, we document several intra...

African Bioacoustics Community conference: Call for Abstracts And Registration now open! 3-7 December 2018 Cape Town We are excited to announce that the first African Bioacoustics Community conference will be held in Cape Town on the 3rd-7th December 2018. Individuals interested in all aspects of Bioacoustic research on any taxa are invited to pa...

In a data poor area such as the Namibian coastline, archived newspapers can be a priceless source of information. In search of historical records about the marine life off the Namibian coast, especially recordings of whale and dolphin strandings, the Namibian Dolphin Project (NDP) looked at the archives of the Namib Times newspaper held at Walvis B...

Humpback whales (Megaptera novaeangliae) are well known for their complex song which is culturally transmitted and produced by males. However, the function of singing behavior remains poorly understood. Song was observed from 57 min of acoustic recording in the presence of feeding humpback whales aggregated in the near-shore waters on the west coas...

Passive acoustic monitoring (PAM) is commonly used to generate information on the distribution, abundance, and behavior of cetacean species. In African waters, the utilization of PAM lags behind most other continents. This study examines whether the whistles of three coastal delphinid species (Delphinus delphis, Tursiops truncatus, and Tursiops adu...

Cetacean watching from tour boats has increased in recent years and has been promoted as an ethically viable alternative to cetacean viewing in captive facilities or directed take. However, short- and long-term impacts of this industry on the behaviour and energetic expenditure of cetaceans have been documented. Although multiple studies have inves...

Cetacean watching from tour boats has increased in recent years. However, short- and long-term impacts of this industry on the behavior and energetic expenditure of cetaceans have been documented. Although multiple studies have investigated the acoustic response of dolphins to marine tourism, there are several covariates that could also explain som...

The use of active acoustic tags to study the movements and behavior of marine animals (mostly teleosts and elasmobranchs) has increased exponentially in the last two decades with over 40 000 tags deployed worldwide. Tags typically produce narrow band time-coded pulses in the 69 or 180 kHz frequency range. There is a growing concern of the impact of...

Marine mammals are important ecological role players in the marine ecosystem that are vulnerable to different pressures that threaten their mere existence. The successful conservation and management of populations of marine mammals depend on the availability of basic knowledge about their population numbers, distribution and/ or migratory patterns,...

Describing the repertoire of sounds produced by wild cetaceans is necessary for understanding their function, for acoustic population monitoring and for measuring the potential influence of anthropogenic impact. Geographic variation in the types and parameters of sounds makes regional assessment of vocal behaviour necessary. We describe the acousti...

Humpback whales (Megaptera novaeangliae) from a breeding ground off Gabon (0–4°S) and a migratory corridor/feeding ground on the west coast of South Africa (WSA; 33°S) differ genetically and in catch histories. Interpretation of the population structure is hampered by the lack of data from the intervening 3,500 km of coastline or to the north of Ga...

Common bottlenose dolphins (Tursiops truncatus) use individually distinctive signature whistles which are highly stereotyped and function as contact calls. Here we investigate whether Indo-Pacific bottlenose dolphins (T. aduncus) use signature whistles. The frequency trace of whistle contours recorded from three genetically distinct free-ranging po...

Dwarf (Kogia sima) and pygmy (K. breviceps) sperm whales occur in pelagic waters around southern Africa. Here we report the first record of K. sima from Namibia and provide information on the basic morphometrics and diet of that record and of two recent strandings of K. breviceps. All known records (N = 29) of K. breviceps from Namibia are also col...

Records of kogiid whales in Namibia, including the first record of the dwarf sperm whale (Kogia sima)—CORRIGENDUM - Volume 6 - S.H. Elwen, T. Gridley, J.-P. Roux, P.B. Best, M.J. Smale

Populations of Indo-Pacific bottlenose dolphin (Tursiops aduncus) are distributed along coastal regions of the south-west Indian Ocean (SWIO), from South Africa to Kenya. An account of whistles from wild T. aduncus inhabiting the SWIO is provided here. Recordings were made at Plettenberg Bay (South Africa) and Zanzibar Island (Tanzania) and the fre...