Mockingbirds in the Galapagos Islands

The mockingbirds of Galapagos recently had their taxonomical status revised. In 1890, they were placed by Ridgeway in a separate and unique genus, Nesomimus. However in 2007 the American Ornithologists' Uniondetermined there was not enough supporting evidence to uphold this distinction and so have been placed into the genus Mimus, in closer company to their cousins the long-tailed mockingbird found on mainland Ecuador and the Chilean mockingbird.

There are four recognized species of mockingbirds in the Galapagos islands: Hood Mockingbird, Mimus macdonaldi, Galápagos Mockingbird,Mimus parvulus, Floreana Mockingbird or Charles Mockingbird, Mimus trifasciatus andSan Cristóbal Mockingbird, Mimus melanotis. On our Galapagos cruise we see one or the other of these species almost every day, depending on the island visited.Some of the species are more curious towards humans than others, such as the Hood or Española mockingbird. On the beaches of the island they are known to hop onto towels or backpacks left alone while the owner takes a swim or walk. All mockingbirds are omnivorous, devouring anything that looks palatable such as insects, young lava lizards and sea lion afterbirth. Well adapted to survive in the arid lowlands of the islands, mockingbirds are experts at finding freshwater from the morning dew off the surface of leaves and rocks. During the rainy season and in the damp highlands, freshwater is plentiful.

Mockingbirds in Galapagos produce possibly the loveliest sounds found in the islands. Chirrups and a wide range of other vocalizations can be heard frequently. Populations are limited for the most part by the annual food production and supply; however they do have a few native predators namely the Galapagos snake, short-eared owl and Galapagos hawk. With the arrival of humans to the islands starting in 1535, black rats were introduced and have thrived in an environment well-suited to their lifestyles: abundant food, plentiful holes and tunnels, and few predators. As a result, the mockingbirds of Galapagos as well as other species, have suffered on islands where rats have established populations.

The Floreana mockingbird, Mimus trifasciatus, unlike the other three species of mockingbirds in the islands, appears to be more terrestrial than the other three species, spending more time on the ground when foraging. This terrestrial lifestyle seems to have led the population to the border of extinction. Indeed, on the main island of Floreana they went extinct 50 years after the visit of the H.M.S. Beagle in 1835. Floreana was one of the first islands to be inhabited by humans, so an early introduction of rats and cats undoubtedly took place very early on. However, off-shore lie two small satellite islets on which these birds have maintained remnant populations, Champion and Gardner-by-Floreana. Recently the Galapagos National Park personnel eradicated introduced fire-ants found on Champion, a situation which could easily have wiped out the entire population of that islet if not discovered in time. With that potential reality in mind, a plan was proposed for a captive-breeding program in order to re-introduce mockingbirds to the main island of Floreana once the introduced rats and cats have been controlled or even eradicated. After genotyping individuals from both islands, microsatellite results showed significant divergence between the extant populations. To discover which was closest to the ancestral population originally found on the island of Floreana, samples were analyzed from museum specimens including two collected on the island of Floreana by Charles Darwin and Robert Fitzroy in 1835. The decision has been made prepare a population using individuals from both gene pools. This will hopefully produce a population of mockingbirds with the maximum diversity possible and hopefully give them the best chances at survival on the main island of Floreana.

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