THE BAT- EARED FOX

 

The bat-eared fox (Otocyon megalotis) is a species of fox found on the African savanna. It is the only extant species of the genus Otocyon^[1] and considered a basal canid species.^[4] Fossil records indicate this canid first appeared during the middle Pleistocene.^[5]

It is named for its large ears, which have a role in thermoregulation.^[3] The bat referred to in its colloquial name is possibly the Egyptian slit-faced bat (Nycteris thebaica), which is abundant in the region and has very large ears.^[6] Although not commonly used, other vernacular names include big-eared fox, black-eared fox, long-eared fox,^[7] Delalande's fox, cape fox,^{[note 1][8]} and motlosi.^[3]

 

Systematics and evolution

 

 

The bat-eared fox is the only living species of the genus Otocyon. Its scientific name, given by Anselme Gaëtan Desmarest, was initially Canis megalotis (due to its close resemblance to jackals), and later changed by Salomon Müller which placed it in its own genus, Otocyon; its huge ears and different dental formula warrant inclusion in a genus distinct from both Canis and true foxes (Vulpes).^[6] The generic name Otocyon is derived from the Greek words otus for ear and cyon for dog, while the specific name megalotis comes from the Greek words mega for large and otus for ear.^[3]

Due to its different dentition, the bat-eared fox was previously placed in a distinct subfamily of canids, Otocyoninae, as no relationship to any living species of canid could be established. However, according to more recent examinations, this species is regarded as having affinities with the vulpine line,^[9] and Otocyon was placed with high confidence as sister to the clade containing both the raccoon dog (Nyctereutes) and true foxes (Vulpes), occupying a basal position within Canidae.^[10][4]

 

Subspecies

Otocyon is poorly represented in the fossil record. It is suggested the genus forms a clade with Prototocyon, an extinct genus of canid. However, the generic distinction between Prototocyon and the extant Otocyon is doubtful.^[11][12] Fossils of an extinct fox-like canine known as Otocyon recki, have been found in sediments of the Olduvai Gorge, Tanzania, dating back to the late Pliocene or early Pleistocene.^[3] However, it is now often placed in Prototocyon.^[13][14]

 

Description

 

Bat-eared foxes are relatively small canids, ranging in weight from 3 kg to 5.3 kg. Head and body length is 46–66 cm, tail length is 23–34 cm, shoulder height is 30–40 cm,^[15] and the notably large ears are 11–13 cm long.^[16]

Generally, the pelage is tan-colored, with gray agouti guard hairs,^[15] giving its grizzled appearance, appearing more buff on the sides.^[9] The undersides and throat are pale. The limbs are dark, shading to dark brown or black at their extremities. The muzzle, the tip and upperside of the tail and the facial mask are black. The insides of the ears are white.^[3] Individuals of the East African subspecies, O. m. virgatus, tend toward a buff pelage with dark brown markings, as opposed to the black of O. m. megalotis. Proportionally large ears of bat-eared foxes, a characteristic shared by many other inhabitants of hot, arid climates, help to distribute heat. They also help in locating prey.^[16]

 

Range and distribution

 

The bat-eared fox has a disjointed range of distribution across the arid and semi-arid regions of Eastern and Southern Africa, in two allopatric populations (representing each of the recognized subspecies) separated by approximately 1,000 km. Subspecies O. m. virgatus extends from southern Sudan, Ethiopia and Somalia, through Uganda and Kenya to southwestern Tanzania; O. m. megalotis occurs in the southern part of Africa, ranging from Angola through Namibia and Botswana to South Africa, and extends as far east as Mozambique and Zimbabwe,^[2] spreading into the Cape Peninsula and toward Cape Agulhas. Home ranges vary in size from 0.3 to 3.5 km².^[3] There are no confirmed observations in Zambia.^[2]

 

Habitat

 

Bat-eared foxes are adapted to arid or semi-arid environments. They are commonly found in short grasslands, as well as the more arid regions of the savannas, along woodland edges, and in open acacia woodlands.^[16] They prefer bare ground and areas where grass is kept short by grazing ungulates^[3] and tend to hunt in these short grass and low shrub habitats. However, they do venture into areas with tall grasses and thick shrubs to hide when threatened.^[17]

In addition to raising their young in dens, bat-eared foxes use self-dug dens for shelter from extreme temperatures and winds. They also lie under acacia trees in South Africa to seek shade during the day.^[3]

 

Diet

Bat-eared foxes are considered the only truly insectivorous canid,^[18] with a marked preference for harvester termites (Hodotermes mossambicus),^[19] which can constitute 80–90% of its diet.^[3]

When this particular species of termite is not available, their opportunistic diet allows a wide variety of food items to be taken:^[19] they can consume other species of termites, other arthropods such as ants, beetles (especially scarab beetles),^[20] crickets, grasshoppers, millipedes, moths, scorpions, spiders, and rarely birds, birds' eggs and chicks,^[21] small mammals, reptiles, and fungi (the desert truffle Kalaharituber pfeilii^[22]). Berries, seeds, and wild fruit also are consumed. The bat-eared fox refuses to feed on snouted harvester termites, likely because it is not adapted to tolerate termites' chemical defense.^[3]

Generally, bat-eared foxes meet their water requirements by the high water content of their diet, water constitutes a critical resource during lactation.

 

Dentition

 

The teeth of the bat-eared fox are much smaller and reduced in shearing surface formation than teeth of other canid species. This is an adaptation to its insectivorous diet.^[23] The bat-eared fox is an old species that was widely distributed in the Pleistocene era. The teeth are not the bat-eared fox's only morphological adaptation for its diet. On the lower jaw, a step-like protrusion, called the subangular process,^{[clarification needed]} anchors the large digastric muscle to allow for rapid chewing. The digastric muscle is also modified to open and close the jaw five times per second.^[3]

 

Foraging

 

Bat-eared foxes usually hunt in groups, often splitting up in pairs, with separated subgroups moving through the same general area.^[24] When termites are plentiful, feeding aggregations of up to 15 individuals from different families occur.^[25] Individuals forage alone after family groups break in June or July and during the months after cub birth.

Prey is located primarily by auditory means, rather than by smell or sight.^[24] Foraging patterns vary between seasons and populations, and coincide with termite availability. In eastern Africa, nocturnal foraging is the rule, while in southern Africa, nocturnal foraging during summer slowly changes to an almost solely diurnal pattern during the winter. Foraging techniques depend on prey type, but food is often located by walking slowly, nose close to the ground and ears tilted forward.^[9] It usually occurs in patches, which match the clumped prey resources, such as termite colonies, that also occur in patches. Groups are able to forage on clumps of prey in patches because they do not fight each other for food due to their degree of sociality and lack of territoriality.^[17]

Behavior

In the more northern areas of its range (around Serengeti), they are nocturnal 85% of the time. However, around South Africa, they are nocturnal only in the summer and diurnal during the winter.^[26]

Bat-eared foxes are highly social animals. They often live in pairs or groups, and home ranges of groups either overlap substantially or very little. In southern Africa, bat-eared foxes live in monogamous pairs with kits, while those in eastern Africa may live in pairs, or in stable family groups consisting of a male and up to three closely related females with cubs.^[27] Individuals forage, play, and rest together in a group, which helps in protection against predators. They engage in frequent and extended allogrooming sessions, which serve to strengthen group cohesion, mostly between mature adults, but also between young adults and mature adults^[3]

Threat display of bat-eared fox

Visual displays are very important in communication among bat-eared foxes. When they are looking intently at something, the head is held high, eyes are open, ears are erect and facing forward, and the mouth is closed. When an individual is in threat or showing submission, the ears are pulled back and lying against the head and the head is low. The tail also plays a role in communication. When an individual is asserting dominance or aggression, feeling threatened, playing, or being sexually aroused, the tail is arched in an inverted U shape. Individuals can also use piloerection, which occurs when individual hairs are standing straight, to make it appear larger when faced with extreme threat. When running, chasing, or fleeing, the tail is straight and horizontal. The bat-eared fox can recognize individuals up to 30 m away. The recognition process has three steps: First they ignore the individual, then they stare intently, and finally they either approach or attack without displays. When greeting another, the approaching individual shows symbolic submission which is received by the other individual with a high head and tail down. Few vocalizations are used for communication, but contact calls and warning calls are used, mostly during the winter. Glandular secretions and scratching, other than for digging, are absent in communication.^[3]

Reproduction

 

The bat-eared fox is predominantly socially monogamous,^[28] although it has been observed in polygynous groups. In contrast to other canids, the bat-eared fox has a reversal in parental roles, with the male taking on the majority of the parental care behavior. Gestation lasts for 60–70 days and females give birth to litters consisting of one to six kits. Beyond lactation, which lasts 14 to 15 weeks,^[3] males take over grooming, defending, huddling, chaperoning, and carrying the young between den sites. Additionally, male care and den attendance rates have been shown to have a direct correlation with cub survival rates.^[29] The female forages for food, which she uses to maintain milk production, on which the pups heavily depend. Food foraged by the female is not brought back to the pups or regurgitated to feed the pups.^[3]

Pups in the Kalahari region are born September–November and those in the Botswana region are born October–December. Young bat-eared foxes disperse and leave their family groups at 5–6 months old and reach sexual maturity at 8–9 months.^[3]

Conservation threats

The bat-eared fox has some commercial use for humans. They are important for harvester termite population control, as the termites are considered pests. They have also been hunted for their fur by Botswana natives.^[3] Additional threats to populations include disease and drought that can harm populations of prey; however, no major threats to bat-eared fox populations exist.^[2]

Notes

THE JAVA- MOUSE DEER

 

The Java mouse-deer (Tragulus javanicus)^[2] is a species of even-toed ungulate in the family Tragulidae. When it reaches maturity it is about the size of a rabbit, making it the smallest living ungulate. It is found in forests in Java and perhaps Bali, although sightings there have not been verified.^[1]

 Java mouse-deer at the Jerusalem Zoo

Taxonomy

 

The Java mouse-deer's common scientific name is Tragulus javanicus, although other classification names for it exist, including Tragulus javanica, Cervus javanicus, and the heterotypic synonym Tragulus fuscatus.^[1][3][4][5] The Java mouse-deer is also known by many common names, including Javan chevrotain, Javan mousdeer, or Java Mouse Deer.^[6] The taxonomic status of the Java mouse-deer is questionable, but recent craniometric analyses have begun to shed light on the taxonomic discrepancies. Previously, the Java mouse-deer, Tragulus javanicus, was commonly thought to represent the wider class of large chevrotains, but it was found that these, unlike the Java mouse-deer, do not likely reside on Java. Three species groups of Tragulus have been identified based on craniometric skull analyses and coat coloration patterns. These three species groups are Tragulus javanicus, Tragulus napu, and Tragulus versicolor. Based upon these craniometric analyses, Tragulus javanicus was then further separated based on the organisms’ known geographic locations: Tragulus williamsoni (found in northern Thailand and possibly southern China), Tragulus kanchil (found in Borneo, Sumatra, the Thai–Malay Peninsula, islands within the Greater Sunda region, and continental Southeast Asia), and Tragulus javanicus (found in Java).^[7] Thus, because of its uniqueness to the island of Java, the Java mouse-deer is now considered a distinct species, although this fact has not significantly affected its current classification.^[8]

 

Appearance and biology

 

Mouse-deer possess a triangular-shaped head, arched back, and round body with elevated rear quarters. The thin, short legs which support the mouse-deer are about the diameter of an average pencil. Although Java mouse-deer do not possess antlers or horns like regular deer, male Java mouse-deer have elongated, tusk-like upper canines which protrude downward from the upper jaw along the sides of their mouth. Males use these “tusks” to defend themselves and their mates against rivals.^[9] Females can be distinguished from males because they lack these prominent canines, and they are slightly smaller than the males.^[6] Java mouse-deer can furthermore be distinguished by their lack of upper incisors. The coat coloration of the Java mouse-deer is reddish-brown with a white underside. Pale white spots or vertical markings are also present on the animal's neck.^[6]

With an average length of 45 cm (18 in) and an average height of 30 cm (12 in), the Java mouse-deer is the smallest extant (living) ungulate or hoofed mammal, as well as the smallest extant even-toed ungulate.^[6][10][11] The weight of the Java mouse-deer ranges from 1 to 2 kilograms (2.2 to 4.4 lb), with males being heavier than females. It has an average tail length of about 5 cm (2.0 in). Mouse-deer are thought to be the most primitive ruminants based on their behaviour and the fossil record, thus they are the living link between ruminants and non-ruminants.^[12][11]

The Java mouse-deer is endothermic and homoeothermic, and has an average basal metabolic rate of about 4.883 watts.^[6] It also has the smallest red blood cells (erythrocytes) of any mammal, and about 12.8% of the cells have pits on them. The pits range in diameter from 68 to 390 nanometres. Red blood cells with pits are unique and have not been reported before either physiologically or pathologically.^[10]

 

Ecology

Tragulus javanicus is usually considered to be endemic to Java, Indonesia. There have been unverified reports of sightings on Bali.^[1]

 

Habitat

 

The Java mouse-deer prefers habitats of higher elevations and the tropical forest regions of Java, although it does appear at lower elevations between 400–700 metres (1,300–2,300 ft) above sea level.^[6][13] During the day, Java mouse-deer can be seen roaming in crown-gap areas with dense undergrowth of creeping bamboo, through which they make tunnels through the thick vegetation which lead to resting places and feeding areas.^[9] At night, the Java mouse-deer moves to higher and drier ridge areas.^[6] It has been argued that Java mouse-deer are an “edge” species, favoring areas of dense vegetation along riverbanks.^[6] Additionally, Java mouse-deer have been found to be more prevalent in logged areas than in the more mature forests, and their densities tended to decrease proportionately as the logged forests matured.

Behavior

Java mouse-deer are primarily herbivores, although in captivity they have been observed to eat insects as well as foliage. Their diet consists primarily of that which they find on the ground in the dense vegetation they inhabit, and they prefer the plants of the faster-growing gap species over the closed forest understory species, likely due to the increased richness of secondary protective compounds which the gap species provide.^[6] They are often classified as folivores, eating primarily leaves, shrubs, shoots, buds, and fungi, in addition to fruits which have fallen from trees.^[6][9] The fruits which Java mouse-deer commonly consume range from 1–5 grams (0.035–0.176 oz), while the seeds range from 0.01–0.5 g (0.00035–0.01764 oz).^[6]

 

Social behavior

 

Groups of Java mouse-deer are commonly referred to as “herds,” while females are termed “does,” “hinds,” or “cows.” Males are referred to as either “bucks,” “stags,” or “bulls,” and their young are commonly called “fawns,” or “asses”.^[9] It was previously believed that Java mouse-deer were nocturnal, but more recent studies have shown that they are neither truly nocturnal nor diurnal, but instead crepuscular, meaning they prefer to be active during the dim light of dawn and dusk.^[9] This behavior has been observed in both wild and captive Java mouse-deer.^[14] Although Java mouse-deer form monogamous family groups, they are usually shy, solitary animals. They are also usually silent; the only noise they make is a shrill cry when they are frightened.

Male Java mouse-deer are territorial, marking their territory and their mates with secretions from an intermandibular scent gland under their chin.^[9] This territorial marking usually includes urinating or defecating to mark their area. To protect themselves and their mates or to defend their territory, mouse-deer slash rivals with their sharp, protruding canine “tusks.” It has also been observed that, when threatened, the Java mouse-deer will beat its hooves quickly against the ground, reaching speeds of up to 7 beats per second, creating a “drum roll” sound.^[15] The territories of Tragulus javanicus males and females have been observed to overlap considerably, yet individuals of the same sex do not share their territories.^[6] When giving birth, however, females tend to establish a new home range. Female Java mouse-deer have an estimated home range of 4.3 hectares (11 acres), while males inhabit, on average, 5.9 hectares (15 acres). Additionally, male Java mouse-deer, in nature, were observed to travel distances of 519 metres (1,703 ft) daily on average, while females average 574 metres (1,883 ft) daily.^[6]

 

Reproduction

 

Java mouse-deer are capable of breeding at any time during the year, and this has been observed during captivity.^[6][13] However, some sources have observed that the breeding season for the Java mouse-deer in nature occurs from November to December.^[16] Additionally, female mouse-deer have the potential to be pregnant throughout most of their adult life, and they are capable of conceiving 85–155 minutes after giving birth.^[13] The Java mouse-deer's gestation period usually lasts 4.5 months, or 144 days.^[6][13] Typical litters consist of a single fawn, which resembles a miniature adult, although the tusk-like incisors prevalent in males are not visible in the young mouse-deer.^[6] The average mass of a newborn fawn is 370 grams (13 oz), and these precocial young are capable of standing within 30 minutes after birth. Fawns are capable of eating solid food within two weeks, yet it takes around 12 weeks to completely wean the fawns.^[9] On average, it takes the young, both male and female, 167 days (~5 months) to reach sexual maturity.^[17] Mouse-deer have been observed to live up to 14 years in captivity, but their lifespan in nature is still an open question.^[6]

 

Predators

 

One of the main predators which the Java mouse-deer face is humans. Through the destruction of their habitat, as well as from hunting and trapping the mouse-deer for food, their pelts, and for pets, humans have considerably reduced the Java mouse-deer population. Mouse-deer are particularly vulnerable to being hunted by humans at night because of their tendency to freeze when illuminated by having a spotlight shone on them.^[1] Because of the small size of the Java mouse-deer, dogs are also a common predator for them, as well as crocodiles, big cats, birds of prey, and snakes.^[15]

 

Diseases

 

Although research into the diseases and parasites which affect the Java mouse-deer are still nascent, bovine viral diarrhea virus (BVDV 1), a pestivirus of the family flaviviridae has been detected in Java mouse-deer. Mouse-deer acquire this virus through fetal infection during early pregnancy. Once acquired, individuals with BVDV can gain lifelong immune tolerance.^[18]

 

Conservation status

 

Java mouse-deer is currently categorized as “Data Deficient” on the International Union for Conservation of Nature's Red List.^[1] This data deficiency is due to the inconclusiveness regarding the distinct separation of Tragulus species, in addition to the lack of information on Tragulus javanicus. Even comparison of past observed numbers of Java mouse-deer with those presently observed does not greatly aid researchers because of the high likelihood of inaccuracy in past observations. Although listed as “Data Deficient,” it is highly probable that a decline in the numbers of Java mouse-deer is occurring, and upon further investigation of this issue, the Red List status of Tragulus javanicus could easily change to “Vulnerable”.^[1] Some conservation actions which have been implemented include legally protecting the species, which, although it has been in effect since 1931, makes no significant difference since hunting of Java mouse-deer still occurs.^{[citation needed]} Additionally, some areas of Java which the Java mouse-deer frequents have been protected, yet enforcement of these regulations is still needed. One of the greatest conservation efforts needed is simply more information about the species: a more complete definition of its taxonomy, as well as more information on its habitat and behavior.

 

Indonesian folklore

 

Historically, the mouse-deer has featured prominently in Malay and Indonesian folklore, where it is considered a wise creature. This character, Sang Kancil (pronounced “Kahn-cheel”), is a diminutive but wise mouse-deer. Sang Kancil is a tiny and cunning hero who, through his intelligence, is able to prevail over his larger tyrants and foes.^[19][20]

 

 

 

THE BEAKEKED WHALE AND WHITE BEAKED DOLPHIN

 

Beaked whales (systematic name Ziphiidae) are a family of cetaceans noted as being one of the least known groups of mammals because of their deep-sea habitat and apparent low abundance.^[1] Only three or four of the 24 species are reasonably well-known. Baird's beaked whales and Cuvier's beaked whales were subject to commercial exploitation, off the coast of Japan, while the northern bottlenose whale was extensively hunted in the northern part of the North Atlantic late in the 19th and early 20th centuries.^[2]

Reports emerged in late 2020 of the possible discovery of a new beaked whale species off the coast of Mexico, the taxonomy of which had not been determined as of December 2020.^[3][4][5][6]

 

Physical characteristics

Blainville's beaked whale

Beaked whales are moderate in size, ranging from 4.0 to 13 metres (13.1 to 42.7 ft) and weighing from 1.0 to 15 tonnes (0.98 to 14.76 long tons; 1.1 to 16.5 short tons). Their key distinguishing feature is the presence of a 'beak', somewhat similar to many dolphins. Other distinctive features include a pair of converging grooves under the throat, and the absence of a notch in the tail fluke. Although Shepherd's beaked whale is an exception, most species have only one or two pairs of teeth, and even these do not erupt in females. Beaked whale species are often sexually dimorphic – one or the other sex is significantly larger. The adult males often possess a large bulging forehead,^[7] some to an extreme feature.^[8] However, aside from dentition and size, very few morphological differences exist between male and female beaked whales.^[9]

Individual species are very difficult to identify in the wild, since body form varies little from one species to another. The observer must rely on often subtle differences in size, color, forehead shape, and beak length. In the skull, the expansion of the prexamillary process can be a key feature to indentification.^[8]

The blubber of these whales is almost entirely (94%) composed of wax ester, a unique characteristic of this family.^[10]

Dentition

 

Beaked whales are unique among toothed whales in that most species only have one pair of teeth. The teeth are tusk-like, but are only visible in males, which are presumed to use these teeth in combat for females for reproductive rights. In females, the teeth do not develop and remain hidden in the gum tissues.^[11]

In December 2008, researchers from the Marine Mammal Institute at Oregon State University completed a DNA tree of 13 of 15 known species of Mesoplodon beaked whales (excluding the spade-toothed whale, which was then only known from a skeletal specimen and a few stranded specimens). Among the results of this study was the conclusion that the male's teeth are actually a secondary sexual characteristic, similar to the antlers of male deer. Each species' teeth have a characteristically unique shape. In some cases, these teeth even hinder feeding; in the strap-toothed whale, for example, the teeth curve over the upper jaw, effectively limiting the gape to a few centimeters. Females are presumed to select mates based on the shape of the teeth, because the different species are otherwise quite similar in appearance.^[11]

The social structure is not well known, but sightings of single males accompanying multiple females suggest a polygynous mating system, which would considerably limit the number of males a female can choose.^[11]

 

Taxonomy

 

Beaked whales comprise at least 22 species. Several species have been described only in the last two decades. Six genera have been identified.

The beaked whales are the second-largest family of cetaceans (after the dolphins). They were one of the first groups to diverge from the ancestral lineage. The earliest known beaked whale fossils date to the Miocene, about 15 million years ago.^[12]

Arnoux's beaked whale

 

 

Evolutionary history

 

As many as 26 genera antedate humans.^[1][16] These include ancestors of giant beaked whales (Berardius), such as Microberardius, and ancestors of Cuvier's beaked whale (Ziphius); they had many relatives, such as Caviziphius, Archaeoziphius, and Izikoziphius. They were probably preyed upon by predatory whales and sharks, including Carcharocles megalodon. Recently,^[when?] a large fossil ziphiid sample was discovered off the South African coast, confirming the extant ziphiid diversity might just be a remnant of a higher past diversity. After studying numerous fossil skulls off the shore of Iberia^[8] and South Africa, researchers discovered the absence of functional maxillary teeth in all South African fossil ziphiids, which is evidence that suction feeding had already developed in several beaked whale lineages during the Miocene. Researchers also found fossil ziphiids with robust skulls, signaling that tusks were used for male-male interactions (speculated with extant beaked whales).^[1]

 

Ecology

 

Diving

 

 

Beaked whales are deep divers with extreme dive profiles.^[17] They regularly dive deeper than 500 m (1,600 ft) to echolocate for food, and these deep dives are often followed by multiple shallower dives less than 500 m.^[18] This pattern is not always followed, however. Animals have been observed spending more than an hour at or near the surface breathing. Beaked whales are often seen surfacing synchronously, but asynchronous surfacing has also been observed.^[19] In March 2014, a study by Cascadia Research revealed that Cuvier's beaked whales were recorded to dive at least 2992 m in depth, a mammalian record.^[20] Another study, published in 2020, reported a Cuvier's beaked whale making a dive that lasted 222 minutes, another mammalian record.^[21]

Deep-diving mammals face a number of challenges related to extended breath-holding and hydrostatic pressure. Cetaceans and pinnipeds that prolong apnea must optimize the size and use of their oxygen stores, and they must deal with the accumulation of lactic acid due to anaerobic metabolism.^[17] Beaked whales have several anatomical adaptations to deep diving: large spleens, livers, and body shape. Most cetaceans have small spleens. However, beaked whales have much larger spleens than delphinids, and may have larger livers, as well. These anatomical traits, which are important for filtering blood, could be adaptations to deep diving. Another notable anatomical adaptation among beaked whales is a slight depression in the body wall that allows them to hold their pectoral flippers tightly against their bodies for increased streamlining.^[9] However, they are not invulnerable to the effects of diving so deep and so often. Cascadia Research shows that the deeper the whales dive, the less often they dive per day, cutting their efforts by at least 40%.^[20]

The challenges of deep diving are also overcome by the unique diving physiology of beaked whales. Oxygen storage during dives is mostly achieved by blood hemoglobin and muscle myoglobin.^[18] While the whale is diving, its heart rate slows and blood flow changes. This physiological dive response ensures oxygen-sensitive tissues maintain a supply of oxygen, while those tissues tolerant to hypoxia receive less blood flow. Additionally, lung collapse obviates the exchange of lung gas with blood, likely minimizing the uptake of nitrogen by tissues.^[9]

 

Feeding

 

The throats of all beaked whales have a bilaterally paired set of grooves that are associated with their unique feeding mechanism, suction feeding.^[9] Instead of capturing prey with their teeth, beaked whales suck it into their oral cavity. Suction is aided by the throat grooves, which stretch and expand to accommodate food. Their tongues can move very freely. By suddenly retracting the tongue and distending the gular (throat) floor, pressure immediately drops within the mouth, sucking the prey in with the water.

Dietary information is available from stomach contents analyses of stranded beaked whales and from whaling operations. Their preferred diet is primarily deep-water squid,^[11] but also benthic and benthopelagic fish and some crustaceans, mostly taken near the sea floor.^[19] In a recent study, gouge marks in the sea floor were interpreted to be a result of feeding activities by beaked whales.^[22]

To understand the hunting and foraging behavior of beaked whales, researchers used sound and orientation recording devices on two species: Cuvier's beaked whale (Ziphius cavirostris) and Blainville's beaked whale (Mesoplodon densirostris). These whales hunt by echolocation in deep water (where the majority of their prey is located) between about 200 and 1,885 m (656 and 6,184 ft) and usually catch about 30 prey per dive. Cuvier's beaked whales must forage on average at 1,070 m (3,510 ft) for 58 minutes and Blainville's beaked whales typically forage at 835 m (2,740 ft) deep for an average of 47 minutes.^[17]

 

Range and habitat

 

The family Ziphiidae is one of the most widespread families of cetaceans, ranging from the ice edges at both the north and south poles, to the equator in all the oceans.^[23] Specific ranges vary greatly by species, though beaked whales typically inhabit offshore waters that are at least 300 m deep.

Beaked whales are known to congregate in deep waters off the edge of continental shelves, and bottom features, such as seamounts, canyons, escarpments, and oceanic islands, including the Azores and the Canary Islands,^[19] and even off the coasts of Hawaii.^[20]

 

Life history

 

Very little is known about the life history of beaked whales. The oldest recorded age is 84 years for a male Baird's beaked whale and 54 years for a female. For all other beaked whale species studied, the oldest recorded age is between 27 and 39 years. Sexual maturity is reached between seven and 15 years of age in Baird's beaked whales and northern bottlenose whales. Gestation varies greatly between species, lasting 17 months for Baird's beaked whales and 12 months for the northern bottlenose whale.^[24] No data are available on their reproductive rates.

Determining group size for beaked whales is difficult, due to their inconspicuous surfacing behavior. Groups of beaked whales, defined as all individuals found in the same location at the same time, have been reported as ranging from one to 100 individuals. Nevertheless, some populations' group size has been estimated from repeated observations. For example, northern and southern bottlenose whales (H. ampullatus and H. planifrons), Cuvier's beaked whales, and Blainville's beaked whales (Mesoplodon densirostris) have a reported maximum group size of 20 individuals, with the average ranging from 2.5 to 3.5 individuals. Berardius species and Longman's beaked whales (Indopacetus pacificus) are found in larger groups of up to 100 individuals.^[19]

Not much information is available about group composition of beaked whales. Only three species have been studied in any detail: northern bottlenose whales, Blainville's beaked whales, and Baird's beaked whales. Female northern bottlenose whales appear to form a loose network of social partners with no obvious long-term associations. In contrast to females, some male northern bottlenose whales have been repeatedly recorded together over several years, and possibly form long-term associations. Studies of Blainville's beaked whales have revealed groups usually consist of a number of females, calves, and/or juvenile animals. These whales are assumed to live in "harem-like" groups, where several females and young are accompanied by a single male.^[11] Baird's beaked whales are known to occur in multiple male groups, and in large groups consisting of adult animals of both sexes. Arnoux's beaked whales have also been observed to form large pods of up to 47 individuals off the Southern Ocean off the coast of Kemp Land, Antarctica.^[25]

 

Conservation

 

For many years, most beaked whale species were insulated from anthropogenic impacts because of their remote habitat. However, now several issues of concern include:

• Studies of stranded beaked whales show rising levels of toxic chemicals in their blubber.^[26]
• As a top predator, beaked whales, like raptors, are particularly vulnerable to build-up of biocontaminants. They can ingest plastic (which can be lethal).^[19]
• They more frequently become trapped in trawl nets, due to the expansion of deepwater fisheries.^[27]
• Decompression sickness

A major conservation concern for beaked whales (family Ziphiidae) is they appear to be vulnerable to modern sonar operations, which arises from recent strandings that temporally and physically coincide with naval sonar exercises.^[28] Mid-frequency active sonar (MFAS), developed in the 1950s for submarine detection, is thought to induce panic when experienced by whales at depth.^[29] This raises their heart-rates, forcing them to attempt to rapidly ascend toward the surface in search of air. This artificially-induced rapid ascent can cause decompression.^[29]

Post mortem examinations of the stranded whales in concurrence with naval exercises have reported the presence of hemorrhaging near the ears or gas and fat emboli, which could have a deleterious impact on beaked whales that is analogous to decompression sickness in humans.^[18] Gas and fat emboli have been shown to cause nervous and cardiovascular system dysfunction, respiratory distress, pain, and disorientation in both humans and animals.^[28] In the inner ear, gas embolism can cause hemorrhages, leading to disorientation or vestibular dysfunction.

Breath-holding divers, like beaked whales, can develop decompression-related problems (the "bends") when they return to the surface after deep dives.^[17] This is a possible hypothesis for the mass strandings of pelagic beaked whales associated with sonar-related activities. To illustrate, a diving beaked whale may be surfacing from a deep dive and must pass vertically through varying received sound levels. Since the whale has limited remaining oxygen supplies at the end of a long dive, it probably has limited abilities to display any normal sound avoidance behavior. Instead, the whale must continue to swim toward the surface to replenish its oxygen stores.^[19] Avoiding sonar inevitably requires a change in behavior or surfacing pattern. Therefore, sonar in close proximity to groups of beaked whales has the potential to cause hemorrhaging or to disorient the animal, eventually leading to a stranding.

Current research reveals two species of beaked whales are most affected by sonar: Cuvier's (Z. cavirostris) and Blainville's (M. densirostris) beaked whales. These animals have been reported as stranding in correlation with military exercises in Greece, the Bahamas, Madeira, and the Canary Islands.^[30] The livers of these animals had the most damage.^[31]

In 2019, a review of evidence on the mass strandings of beaked whale linked to naval exercises where sonar was used was published. It concluded that the effects of mid-frequency active sonar are strongest on Cuvier's beaked whales but vary among individuals or populations, and the strength of their response may depend on whether the individuals had prior exposure to sonar. The report considered that the most plausible explanation of the symptoms of decompression sickness such as gas embolism found in stranded whales to be the whales' response to sonar. It noted that no more mass strandings had occurred in the Canary Islands once naval exercises where sonar was used were banned there, and recommended that the ban be extended to other areas where mass strandings continue to occur.^[32][33]

Four species are classified by the IUCN as "lower risk, conservation dependent": Arnoux's and Baird's beaked whales, and the northern and southern bottlenose whales. The status of the remaining species is unknown, preventing classification.^[34]

 

Captivity

 

Beaked whales live very short lives in captivity when compared to other cetaceans such as common bottlenose dolphins and short-finned pilot whales,^[35] most surviving only a few days out of the ocean.^{[36][better source needed]} The longest time period for a beaked whale living in captivity was 25 days. Alexander and Nicholas, two male beaked whales—their species unknown, though they were thought to be either Hubbs' beaked whale or Blainville's beaked whale—had become stranded in California on 24 August 1989. They were taken to Marine World California.^[37] Both of the whales would die of pneumonia; Nicholas died on 8 September and Alexander died 10 days later.^[38]

A handful of other beaked whales have been briefly kept in captivity. A juvenile female Cuvier's beaked whale was found stranded on a kelp bed off of Santa Catalina Island on 23 February 1956. She was taken to Marineland of the Pacific, where she was named Martha Washington.^[39] On 16 June 1969, a Cuvier's beaked whale live stranded in St. Augustine. The whale, thought to be a male, was then transported to Marineland of Florida. It is unknown what happened to the whale, but it was still alive on 18 June 1969.^[40]

 

References