The variety of mammal species in the Galapagos Islands is rather limited, as is typical for most islands located far from mainland continents. In fact, there are only 6 mammal species (that can be found on land) that are considered native to the islands, plus a number of aquatic mammals that swim in and out of the Galapagos Marine Reserve.
With a population size of about 50,000, the Galapagos Sea Lion (Zalophus californianus, subspecies: wollebacki) is one of the first animals that visitors to the Galapagos Islands encounter. They can often be found sprawled on the docks or benches where tourists board their cruise boats, and are found lounging on beaches or low rocky shorelines throughout the islands. Their playful and inquisitive behavior makes them a tourist favorite, and lucky divers or snorkelers may be treated to underwater gymnastic displays from these graceful creatures. Despite their curiosity, sea lions are wild animals and can be unpredictable in their behavior – especially the males – and people will occasionally be bitten for not respecting their space and privacy.
Sea Lions are the largest animals found in Galapagos – full-grown males (bulls) can weigh up to 550 pounds. Besides their larger size, males differ from females in that they have a large “bump” on their foreheads and have extremely thick necks that provide protection.
Sea Lions mainly eat fish that they catch out in ocean on extended foraging trips. When on land, they congregate in harems (a group of females with one dominant male bull) or in bachelor colonies (males without harems to defend). However, females are free to move from harem to harem, as it is the territory where the females lie that a dominant bull defends, more so than the actual females in the territory. A dominant bull will spend the majority of his day patrolling the shallow coastal waters along his territory, ensuring that other bulls do not come near. It is exhausting to defend a harem, and for this reason, defense of a harem generally only lasts for a few days up to three months for a single bull. Fights between bulls for territories are quite common, with pushing, neck-biting, and dramatic water chase scenes ensuing. Harems are usually found in the most desirable beach locations, and the bachelor colonies are located in less desirable places, sometimes high atop rocky cliffs or farther inland near lagoons.
Once a year, females give birth to single pups, which they rear for one to three years. For this reason, it is common to see one mother with two suckling pups of different ages. Mothers will stay with their newborn pups for about 5 days, as they get to know each other’s sounds and smells, and then she will venture out to fish and replenish her energy. Baby sea lions will gather in shallow water nurseries that are watched over by one female, while the other mothers go out fishing. Bulls will even join in defending the nurseries from sharks, who may come looking for a defenseless pup meal. At about five months old, young sea lions will begin to learn to fish on their own.
Females are sexually mature at around 5 years old, and can live to be about 20 years old – males mature a bit more quickly, but will not guard a harem until they are older, and they do not live as long as females.
Many people think Galapagos Fur Seals (Arctocephalus galapagoensis) are much less abundant in Galapagos than Sea Lions, but their population numbers are similar. Fur Seals typically prefer more rugged, rockier, and shadier shores than sea lions in areas that less likely to be frequented by people. Fur seals are less tolerant of heat than sea lions, which is why they prefer cooler water and shaded areas. And despite their “seal” name, they are actually a type of sea lion.
Galapagos Fur Seals and Sea Lions are morphologically similar, but there are some key physical differences that can help people tell them apart. Fur seals are generally smaller with broader and shorter heads. Fur Seals have bulging eyes and ears that protrude more than sea lions’, and larger front flippers that aid in climbing rockier coasts. The biggest difference is probably in their fur coat, which is much thicker and appears “furrier” on fur seals than on sea lions.
Because of their remarkably insulating coats, fur seals were hunted by the tens of thousands in the 1800s, nearly to extinction. They have made an amazing comeback in their population numbers, and can be seen most easily by Galapagos tourists at James Bay on Santiago Island and in Darwin Bay on Genovesa Island.
Fur seals eat fish and squid, and they are nocturnal hunters. Scientists have found that they tend to hunt less when the moon is full, probably because they become more visible to shark predators and their prey tends to move into deeper waters.
Fur seals’ social and breeding behaviors are quite similar to that of sea lions (see above), with a few differences. With regards to bulls defending territories, a fur seal bull will defend his harem from land, rather than from the water. Pups begin to hunt at about a year old, but will suckle from their mothers for two to three years. Though females can give birth every year, they will, at most, successfully raise one pup every two years. Should a second pup be born while a yearling is still suckling, the new pup has little chance of survival, despite being defended by its mother.
Unfortunately, only four of the original seven endemic Rice Rat species still exist in Galapagos; not surprisingly, these four species live on three islands that are not inhabited by humans – Santa Fé, Santiago, and Fernandina. The other three species of rice rats became extinct since humans colonized the islands and brought black rats with them. Competition with and/or a virus carried by the black rats is likely what brought about the demise of these three species.
The ancestors of the native rats of Galapagos originally arrived to the Islands via rafts of vegetation that floated from the South American mainland out to Galapagos – these rats actually hold the world record for terrestrial mammal ocean crossings.
There are two bat species present in Galapagos, but little is actually known about them.
Lasiurus cinereus, the Hoary Bat from North America, is light brown with white fur tips, eats insects, and tends to prefer roosting in Mangrove trees or scrub bushes during the day. It is quite widespread and is found on Santa Cruz, San Cristóbal, Isabela, Santiago, and Floreana Islands.
Lasiurus brachyotis is found on Santa Cruz and San Cristóbal in the highlands and coastal zones, and it is believe to migrate seasonally between the two zones. This bat forages near the ground while the Hoary Bat forages higher in the trees and air, which explains why they can coexist. L. brachyotis is believed to be closely related to the Red Bat of South America.
DOLPHINS and WHALES
The aquatic mammals (cetaceans – whales, dolphins) form the last group of mammals found in the Galapagos Islands. Unlike most land mammals that are generally covered in hair or fur, these aquatic mammals have little, if any, hair. Instead, they have a fat layer of blubber which helps to maintain their body heat and to provide a reserve of energy when needed during long migrations or strenuous activity.
The blubber of whales can be used to make oil, and this is what made them so valuable to humans in the 19th century when the Galapagos Islands were central to Pacific whaling activities. Fortunately today, whaling does not take place anymore in the Islands. Whales are occasionally seen passing through Galapagos, and dolphins are likely to be seen all around the islands.
The Cetaceans fall into two major groups – those with teeth, and those with baleen (fringed whalebone that enables filter-feeding of plankton and small marine animals). Both groups of cetaceans, and several species from each group, can be found in the Galapagos Islands. Humpback whales are one of the easier baleen whales to identify because of their angled back, as well as their tendency to breach and splash dramatically back into the sea.
Many species of toothed whales show up in the Galapagos Marine Reserve, including the Sperm Whale, Killer Whale, False Killer Whales, the Pilot Whale, as well as several species of dolphins. There are two dolphin species that are quite abundant and easy to spot– the Bottle-nosed Dolphin and the Common White-bellied Dolphin. The Bottle-nosed Dolphins are often found racing alongside boats, and sometimes they get close enough that people on board can hear their delightful squealing. Common Dolphins are more likely to be found in large schools of 100 or more individuals.