Dolphin Behavior, Sex and Reproduction

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common dolphin

Dolphins can be diurnal (active during the daytime), nocturnal (active at night), motile (move around as opposed to being stationary), nomadic (move from place to place, generally within a well-defined range), migratory (make seasonal movements between regions, such as between breeding and wintering grounds), sedentary (remain in the same area), solitary social colonial (living together in groups or in close proximity to each other), and have dominance hierarchies (ranking systems or pecking orders among members of a long-term social group, where dominance status affects access to resources or mates). [Source: Eric J. Ellis and Allison Poor, Animal Diversity Web (ADW) /=]

According to National Geographic: Dolphins seem to sleep with only half their brains resting at a time. Their eyes operate independently of each other. At water park shows they’ve been trained to corkscrew through the air on command, skate backward across the surface of the water while standing upright on their tails, and wave their pectoral fins at the tourists. They “see” with sonar and do so with such phenomenal precision that they can tell from a hundred feet away whether an object is made of metal, plastic, or wood. They can even eavesdrop on the echolocating clicks of other dolphins to figure out what they’re looking at. [Source: Joshua Foer, National Geographic, May 2015]

Craig Welch wrote in National Geographic: For decades we’ve packed marine theme parks, applauding bottlenose dolphins that sing or vault through hoops in giant pools. These feeble attempts to corral their skills barely scratch the surface of their talents. In 1972 a scientist studying a bottlenose dolphin calf named Dolly exhaled cigarette smoke onto the window of her enclosure during a break. “The observer was astonished when the animal immediately swam off to its mother, returned and released a mouthful of milk which engulfed her head, giving much the same effect as had the cigarette smoke,” researchers wrote at the time. [Source: Craig Welch, National Geographic, April 15, 2021]

Daily activity patterns of dolphins are poorly understood. Most activity is observed in the daytime as this when observations by scientists are most easily made. Spinner dolphins are known to feed at night. Dolphins sometimes ground themselves en masse on beaches and die like pilot whales. Scientist are not sure why they do this. They speculate that perhaps it is caused by disease or parasites. See Whales.

Dolphin One-Eyed Sleep

20120522-Species Rough_toothed_dolphin.jpg
Rough-toothed dolphin
Dolphins sleep only two or three hours day. Dr. Sam Ridgeway of the U.S. Naval Ocean System center says "curiously, they seem to be able to sleep with one eye open, and with half the brain still awake." Often they don't sleep at all.. Sometimes when they rest one side of the brain sleeps while the other is awake. When the one side wakes up the other side sleeps.

Among reasons why they don’t sleep or sleep so little seems to be the need to be on the alert for predators and the fact must surface to breathe every few minutes. When they do sleep they either drifting on the surface, where they can breath, or take a lung full of oxygen and dive to the seabed and lay down there. open. Those that rest or sleep on near surface swim slowly and rise to the surface every minute or so to breath. Spinner dolphins go to specific areas to rest and relax during the day, presumably so they are ready for hunting at night. [Source: Edward J. Linehan, National Geographic, April 1979]

Dolphins rest one side of their brains while decreasing their activity level. This allows them to rest and yet remain ‘conscious’ to breathe and carry on basic survival behaviors. By sleeping with only half of their brains at a time dolphins have the ability to stay constantly alert for at least 15 days in a row. Rachel Nuwer wrote in Even in this seemingly sleep-deprived condition, the aquatic mammals can perform with near-perfect accuracy when using echolocation to identify targets and monitor their environment, according to research from the journal PLoS One. Just two dolphins — a male and female — took part in the study. The pair showed no signs of fatigue for the first five days of the experiment, and the female powered through additional tasks for the entire 15-day period. The researchers cut the study off at that point, so it’s possible that the two dolphins could have continued to perform normally for an indefinite period of time without a full-brain rest. [Source: Rachel Nuwer,, October 19, 2012]

The researchers call the dolphins’ trick for staying alert unihemispheric sleep, or just shutting half of the brain down at a time. They think this technique evolved to allow dolphins to breathe at the surface of water, even when snoozing. “These majestic beasts are true unwavering sentinels of the sea,” said lead researcher Brian Branstetter of the National Marine Mammal Foundation, in a statement. “The demands of ocean life on air breathing dolphins have led to incredible capabilities, one of which is the ability to continuously, perhaps indefinitely, maintain vigilant behavior through echolocation.”

Dolphin Pods and Social Behavior

20120522-NOAA_Photo_Library.jpg Dolphins are social animals that are generally found in groups called pods. They can be found alone and in groups that range from small, unstable associations to herds of hundreds or even thousands of animals. These social groups usually consist of larger number of females than males — typically with a ratio around 60 percent females to 40 percent males. In these pods there will be foraging individuals that hint for prey, and other individuals that care for the young. Some species such as bottlenose dolphins are known to form lasting social bonds with individuals of both sexes. Some cetacean species frequently travel in mixed-species groups. For example, Fraser's dolphins are often observed in association with melon-headed whales. [Source: Eric J. Ellis and Allison Poor, Animal Diversity Web (ADW) /=]

Mothers and their calves are the main components of large bottlenose dolphin social groups that often include three generations. These social groups are often part of large communities that include the roving males in a specific area. Males often pair off with unrelated males in early life and form bonds that last their entire lives. Theses males often surface and breath at the same time when swimming together.

Joshua Foer wrote in National Geographic: “Dolphins are extraordinarily garrulous. Not only do they whistle and click, but they also emit loud broadband packets of sound called burst pulses to discipline their young and chase away sharks. “A dolphin alone is not really a dolphin,” says Lori Marino, a biopsychologist and executive director of the Kimmela Center for Animal Advocacy. “Being a dolphin means being embedded in a complex social network. Even more so than with humans.”

“Richard Connor, who studies the social lives of dolphins in Shark Bay, Australia, has identified three levels of alliances within their large, open social network. Males tend to form pairs and trios that aggressively court females and then keep those females under close guard. Some of these pairs and trios are remarkably stable relationships that can last for decades. Males are also members of larger teams of 4 to 14, which Connor dubs second-order alliances. These teams come together to steal females from other groups and defend their own females against attacks, and they can remain intact for 16 years. Connor has observed even larger, third-order alliances that coalesce when there are big battles between second-order alliances.

“Two dolphins can be friends one day and foes the next, depending on which other dolphins are nearby. Primates tend to have a “you’re either with us or against us” mentality when it comes to making distinctions within and between groups. But for dolphins, alliances seem to be situational and extremely complicated. The need to keep track of all those relationships may help explain why dolphins possess such large brains.

Dolphin Emotion, Grief and Sorrow

Dolphins spend a lot of time each day caressing one another. Sometimes they even rub up against boats in a friendly way. Some say their social behavior is similar to that of lions. Joshua Foer wrote in National Geographic: “When dolphins are in trouble, they display a degree of cohesiveness rarely seen in other animal groups. If one becomes sick and heads toward shallow water, the entire group will sometimes follow, which can lead to mass strandings. It’s as if they have a singular focus on the stranded dolphin, Marino says, “and the only way to break that concentration may be to give them something equally strong to pull them away.” A mass stranding in Australia in 2013 was averted only when humans intervened, capturing a juvenile of the group and taking her out to the open ocean; her distress calls drew the group back to sea. [Source: Joshua Foer, National Geographic, May 2015]

Bottlenose dolphins demonstrate epimeletic behavior (assisted or staying near a distressed, injured, or dead individual). They have been observed helping injured dolphins recuperate. by protecting the injured dolphin from threats as well as holding the injured dolphin at the surface. Epimeletic behavior is most commonly found among mothers of calves that have died. [Source: Jessica Jenkins, Animal Diversity Web (ADW)]

Dolphins are said to feel sorrow. A Croatian newspaper reported that a dolphin appeared to beach itself near the southern Adriatic town of Ploce in an apparent suicide attempt after its offspring perished a few days before at the same spot. According to the newspaper fisherman found a dead baby striped dolphin, then a couple days later they observed an older striped dolphin trying to beach itself. Attempts to lead the dolphin back out to sea only resulted in the dolphin trying to beach itself again.

Dark Side of Dolphins

Bottlenose dolphins often scrape each other with their teeth and occasionally inflict broken jaws. Dolphins are one of the few large animals that seems to kill for the fun of it and commit acts of infanticide. Off Scotland, a scientist once watched in horror as an adult dolphin picked up an infant dolphin in its mouth and beat it against the water repeatedly for an hour. Off Virginia, researchers found nine dead baby dolphins, with their skulls and ribs smashed and teeth marks matching those of adult dolphins. Many dolphins bear scars from encounters with sharks. Sometimes sharks attack dolphins and sometimes dolphins attach sharks, but most of the time they ignore each other. Scientist have seen a pilot whale helping a sick Dall's porpoise. [Source: Edward J. Linehan, National Geographic, April 1979]

At Strangford Lough in Northern Ireland, drone footage seemed show two bottlenose playing with a third dolphin. "But they weren't playing with another dolphin, they were attacking and killing a harbour porpoise and this is something that bottlenose dolphins do quite routinely," Pádraig Whooley, of the Irish Whale and Dolphin Group (IWDG), told the BBC. "People are absolutely horrified because they think, dolphins - aren't they supposed to be cute and cuddly? We've been saying for 30 years, dolphins and in particular bottlenose dolphins, are definitely a species whcih have a dark side...They're big mammals and like lots of big mammals they kill lots of things and they're not even going to eat it." [Source: Niall Glynn, BBC News, April 29, 2023]

Some threats they face are natural. A number of porpoise carcasses found in Scotland all had similar puncture and bruise wounds, with most of them dying as a result of internal injury. In addition to these injuries some of the specimens also had teeth gouges in their flesh. After analyzing these bite patterns, the researchers determined that common bottlenose dolphin were responsible for inflicting these wounds.

In 2023, there were reports of a dolphin 'bullied' by other dolphins that refused to leave a freshwater creek in Virginia. Scientists said the gray bottlenose dolphin was "probably" getting beat up by other dolphins and lived for at least three weeks in a freshwater creek, where it was at risk of dying. Dolphin skin is not designed to be in fresh water and eventually it starts to break down and diseases and bacteria starts to colonize its skin. [Source: Hannah Getahun, Business Insider, April 3, 2023]

Dolphin Playfulness

Dolphins are well known their playfulness. Dolphins are often seen leaping high out of the water and doing flips. The can reach heights of over 15 feet and also "tail-walk" across the water by beating their fluke back and forth near the surface of the water. Some dolphins spyhop — rear up out of the water to look around — presumably to see if predators or prey is around. Trained dolphins have been taught do multiple flips and twirls, and wave at the audience with their flukes and fins.

Dolphins often ride and leap out from bow waves created by large ships. Their superb swimming and navigation skills keeps them from hitting the ships. Some dolphins like to do this and some don't. Dolphin scientist Randall Wells told Discover, "They're definitely individuals; they have their own ways of doing things. Some will quickly come up to the boat and some never do. Some will look at you and others don’t seem to care."

Dolphins Hold Grudges — Only Help Those Who Have Helped Them

Dolphins hold grudges, scientists argue, as they will only help those who have come to their aid in the past. The Telegraph reported: Dolphins form social groups and friendships based on a history of co-operative behaviour which is similar to humans, according to University of Bristol researchers. If a dolphin helps a fellow group member when it's in danger, that comrade is likely to return the favour, they found. This goodwill extends to dolphins which have helped a fellow group member. “However, if a dolphin shirks their responsibility and swims away, and the dolphin in danger survives to remember the incident, they will not help that negligent member in the future — suggesting they hold a grudge. [Source: Phoebe Southworth, The Telegraph, April 23, 2021]

“The findings are based on 30 years of observations of Bottlenose dolphins living in Shark Bay, Western Australia. Drones were flown above dolphin groups and their behaviour was recorded. Dr Stephanie King, from Bristol's School of Biological Sciences, said: "Social animals can possess sophisticated ways of classifying relationships with members of the same species. In our own society, we use social knowledge to classify individuals into meaningful groups, like sports teams and political allies. Bottlenose dolphins form the most complex alliances outside humans, and we wanted to know how they classify these relationships."

“Biologists used sound playback experiments to assess how male dolphins responded to the calls of other males in what they call their "alliance network". The animals work together for a number of reasons, including teaming up to attack or protect themselves from opposing groups, the study found. The research team discovered males responded strongly to all of the allies that had consistently helped them out in the past, even if they weren't currently close friends. However, they didn't respond strongly to males who hadn't come to help in the past, even if they were friends.

“Dr King added: "Such concepts develop through experience and likely played a role in the co-operative behaviour of early humans. "Our results show that cooperation-based concepts are not unique to humans, but also occur in other animal societies with extensive co-operation between non-kin." The findings were published in the journal Nature Communications.

Dolphin Greetings and Friendship

Dolphins have unique whistles for their friends. National Geographic reported: In the animal kingdom it’s common for creatures in the same social circles to adopt similar calls. For years researchers assumed dolphins did the same. But as Stephanie King, a biologist at the University of Western Australia, spent time recording male bottlenose dolphin vocalizations in Shark Bay, she realized that individuals were using unique whistles, even within tight-knit groups. King deduced in a recent study that these calling cards, or “names,” help dolphins keep track of “who their friends are, who are their friends’ friends, and who are their competitors,” she says. Next King will use these calls to learn how male dolphins form and maintain individual social relationships. A lot of this feels familiar to her. “There are a number of striking similarities between human and dolphin societies,” she says. [Source: Nina Strochlic, National Geographic, November 2018]

Bottlenose dolphins exchange signature whistles with each other when they meet in the open sea, which some scientists have described as a greeting or form of conversation. Jennifer Viegas wrote: Earlier research found that signature whistles are unique for each dolphin, with the marine mammals essentially naming themselves and communicating other basic information. A signature dolphin whistle in human speak, might be comparable to, "Hi, I'm George, a large, three-year-old dolphin in good health who means you no harm." [Source: Jennifer Viegas, Discovery Channel, NBC News, Feb. 29, 2012]

The latest study, published in the Proceedings of the Royal Society B, is the first to show how free-ranging dolphins in the wild use these whistles at sea. The findings add to the growing body of evidence that dolphins possess one of the most sophisticated communication systems in the animal kingdom, perhaps even surpassing that of humans. "In my mind, the term 'language' describes the human communication system; it is specific to us," co-author Vincent Janik of the University of St. Andrews Sea Mammal Research Unit, told Discovery News. "It is more fruitful to ask whether there are communication systems with similar complexity. I think the dolphin system is probably as complex as it gets among animals."

Dolphin Sex

Dolphins are viviparous, meaning they give birth to live young that developed in the body of the mother, and engage mostly in seasonal breeding but sometimes breed year-round Females have an estrous cycle, which is similar to the menstrual cycle of human females.Most dolphins species have just one mating season per year. Females each give birth to a single calf every one to six years, after a 10 to 17 month gestation. Dolphins are difficult animals to study, especially their mating practices, and for this reason much about their reproduction remains a mystery. Most species are polygynandrous (promiscuous), with both males and females having multiple partners. [Source: Eric J. Ellis and Allison Poor, Animal Diversity Web (ADW)]

Dolphins can be horny creatures. They often seen mating and engaging in other sexual activities. Maybe that is the real reason they have such big smiles. In Britain a swimmer was once accused of molesting a dolphin. But later biologist explained that male dolphins often rub their penis against other dolphins as a greeting.

Dolphins usually mate to produce calves in the spring, with females often linking up with a roving male. Adult males often enter the territories of other males to make mischief and mate with new females. According to one study about 30 percent of calves are fathered by males that are not part of the community.

Males sometimes appear to gang rape females. Describing one pair of males around a female dolphin researcher Ester Quintana told Discover, "One was under the female and the other was trying to mount her — like a sandwich. They tried for 20 minutes." She doesn't think it was an isolated case. "We see pairs of males isolating a female from the group and flanking her, a male on each side. Sometimes they flank her for hours to a week.”

Dolphins have a very irregular ovulations cycle. Using ultrasound technology scientist at aquariums have been able to predict ovulation and produce dolphin offspring through artificial insemination. Females can reproduce for a long time. The oldest known reproducing female was still making babies at the age of 49.

Dolphin Mothers and Their Calves

Dolphin young are precocial. This means they are relatively well-developed when born. During the pre-fertilization, pre-birth, pre-weaning and pre-independence stages provisioning and protecting are done by females. The post-independence period is characterized by the association of offspring with their mother. There is an extended period of juvenile learning. Parental care provided by males. is rare, but males have been reported anecdotally to show interest in their offspring and bring them food. [Source: Eric J. Ellis and Allison Poor, Animal Diversity Web (ADW) /=]

Bottlenose dolphin with young
After a gestation period of around one year a three-foot-long calf is born tail first and has to be able to swim from the moment they are born.. If it was born headfirst it might drown. After the calf is born the mother darts away quickly to break the umbilical chord and allow the calf to swim to surface for is first breaths of air. Often, swimming by the mother is a "midwife" female who helps the calf to the surface for its first breath and then sticks with the mother for several weeks to help protect the calf and babysits when the mother fetches food. [Source: Robert Leslie Conley, National Geographic, September 1966 ┵]

Females provide their young with milk extremely rich in protein and fat for at least six months. They are attentive mothers, helping their calves reach the surface to take their first breaths after they are born and keeping an eye out for predators. Among some species mothers and calves form associations that last long after calves are weaned. First time mothers need some time to develop their mothering skills it appears. According to one study 85 percent of first born dolphins only survive until adulthood. Offspring born later have a better chance of survival.

Females often nurse their calves over two years and may nurse them for several years. The female has a special set of muscles near her milk-producing glands. When her calf nuzzles the female squirts milk into the baby's mouth. The squirt only last for a few seconds to give the calve time to rise to the surface for air. The process is repeated several times until the calf is full. ┵

Dolphin Young

Calves grow quickly but do not reach sexual maturity for at least two years. Even after sexual maturity, dolphins may have to wait several years before they are socially mature enough to breed.

Young dolphins usually begin eating fish at about the age of six months, sometimes taking large prey and hitting it against the sea floor or smacking it on the ocean surface to break it into small easy-to-digest pieces. Young dolphins also catch and release their prey, apparently for the fun for it and to improve their hunting skills.

Dolphin fetus
Calves don’t sleep their first month of life. After that they sleep only for short periods of time. Their mothers too get little sleep because they are almost constantly tending or watching over their young. It is believed that prolonged wakefulness by the mother: 1) protects the newborn from predators; 2) ensures the calf doesn’t drown while sleeping; and 3) keeps the calf warm until it has amassed enough blubber to warm itself.

Young dolphins play by chasing one another through the water. Adolescent dolphins of both sexes join juvenile groups that goof around, have sex and act rowdy like human teenagers. When females become pregnant they join a group made up of female-calf pairs.

Image Sources: 1) Wikimedia Commons; 2) NOAA; 3) Mikurashima tourism

Text Sources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated June 2023

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