The Socorro dove and the race to reintroduce it on Socorro

Originally, the Socorro dove was widespread on the remote volcanic Pacific island of Socorro, part of the Revillagigedo Islands. But human influences such as introduced predators and the destruction of its habitat wiped it out in the wild. Today, only about 189 individuals still exist worldwide, kept in zoos and conservation programs. These breeding efforts are the last hope for the reintroduction of this species.

Its habitat consisted mainly of densely wooded areas above 500 meters in elevation that provided food and nesting opportunities. As a predominantly terrestrial fruit eater, it inhabited open scrubland and the edges of tropical cloud forests, where it found seeds, berries, and other plant food.

Socorro dove – fact sheet

alternative names	Socorro ground dove, Grayson’s dove
scientific names	Zenaida graysoni, Zenaida macroura graysoni
original range	Socorro (Pacific)
threats	animals introduced to the island, hunting, habitat loss
IUCN status	extinct in the wild

Taxonomically, the Socorro dove belongs to the genus of mourning doves (Zenaida) and thus to the true pigeons and doves (Columbinae). However, its precise classification has occasionally been discussed in the past. Some older sources see affinities with the ground-dwelling American quail-doves or ground doves (Geotrygon), but modern taxonomy does not support this.

The disappearance of the Socorro dove

For thousands of years, the habitat of the Socorro dove remained almost untouched, until human intervention permanently disrupted the island’s ecological balance. The disappearance of the dove began with the construction of a Mexican military base from 1957 onward. This was accompanied, from the early 1970s, by the increasing introduction of feral cats that preyed on the doves. Because of its tameness, the Socorro dove was almost defenseless against the introduced cats. Pigs brought to the island also destroyed the vegetation and the birds’ nesting sites.

Additional factors, such as human hunting, intensive grazing by sheep introduced from 1869 onward, and recurring swarms of the Central American locust Schistocerca piceifrons, contributed to the drastic decline.

Even in 1957 and 1958 there were no signs of a declining population, but only a few years later the numbers collapsed. According to an article (1996) by Juan Martinez-Gómez and Luis F. Baptista, the Socorro dove was last seen in the wild in 1972—almost 100 years after its first scientific description by the American amateur ornithologist George Newbold Lawrence. After extensive searches, it was officially declared “extinct in the wild” in 1983. The International Union for Conservation of Nature (IUCN) confirms that all potential habitats on the island have since been searched without success.

Life in zoos and breeding difficulties

During an expedition in 1925, several Socorro doves were captured and bred in breeding programs in the USA from 1926 onward. Some of these birds later reached Europe. It is likely that only this prevented the species from disappearing completely. These breeding programs are crucial for preserving the genetic diversity of the Socorro dove population and making a successful reintroduction possible. Yet practice shows that captive breeding does not always proceed smoothly.

Socorro doves are considered aggressive toward conspecifics, which makes keeping them together in aviaries difficult. In addition, there is an imbalance in the sex ratio, as there is often a surplus of males. At Burgers’ Zoo in Arnhem (the Netherlands), for example, only a single breeding pair therefore lives in a separate aviary, while the young birds can fly freely in the so-called “Desert” section to avoid conflicts.

Another problem is hybridization with closely related dove species, especially with the mourning dove (Zenaida macroura). According to various reports, crossings occur frequently in the USA and Mexico, so that almost all privately kept birds as well as several individuals from breeding programs are considered hybrids or are at least strongly suspected of being so. Because the Socorro dove has unique adaptations, such hybrids are excluded from reintroduction so that no distorted genetic basis is released.

In his book Last Animals at the Zoo (1993), the biologist Colin Tudge also expressed doubt that a superspecies formed from Socorro doves and mourning doves could ensure the survival of the pure Socorro dove. According to this view, hybrid lines do not replace the special genetic identity and ecological function of the Socorro dove, but could instead lead in the long term to the loss of traits indispensable for reintroduction.

All these factors make it harder to build a stable reserve population. Nevertheless, zoos and institutions around the world are working to preserve the population and its genetic diversity. Today, the Socorro dove is kept in 46 institutions worldwide, and since 1994 at least 70 institutions have participated in breeding. The European breeding program, recognized in 1995 as the European Endangered Species Programme (EEP), is supported by zoos such as Cologne and Frankfurt and by a private interest group for wild doves. Modern studbook software is used to optimize the genetic and demographic management of the population.

The entire population in human care currently amounts to 189 individuals (according to the most recently published figures). To build a genetically independent reserve population closer to the original habitat, twelve birds were moved to Albuquerque Biological Park in New Mexico in 2006. In 2013 and 2014, another transfer of Socorro doves to Mexico followed, where a national breeding group was to be established. The Vogelpark Marlow (Germany) also has a special breeding station for this species. If these populations can be carefully managed and separated from hybrid lines, a later release could at least be prepared in theory.

New developments

According to a report on the London Zoo website, three Socorro doves were transferred from Lagos Zoo (Portugal) to London Zoo at the end of 2024, while two more doves moved to Chester Zoo. This event is seen as a major milestone for the international Socorro Dove Project, a global partnership that plans to reintroduce the Socorro dove to Socorro by 2030.

After arriving at London Zoo, the doves were first kept in quarantine and then carefully introduced to potential partners. For breeding, direct pairings as well as foster parents are used (for example European turtle doves), which prove more successful at incubating eggs. The goal is to form stable breeding pairs that will produce enough offspring for a later release.

Socorro: Measures to restore habitat

For the Socorro dove to one day return to its original home, extensive measures are needed to restore its habitat. The IUCN has summarized the measures taken so far: an important first step was the designation of the Revillagigedo Islands as a biosphere reserve in 1994. In that context, targeted efforts began to remove invasive animal species that threatened the ecological balance on Socorro and thus also the dove population. Between 2009 and 2012, more than 1,700 feral sheep were removed from the island, so that sheep have been considered completely eradicated there since 2012. Thanks to this measure, the vegetation was able to recover quickly, restoring important breeding and feeding areas for the Socorro dove.

Another problem was—and still is—feral cats. Although the cat population was significantly reduced between 2011 and 2016, they have not disappeared completely. The same applies to introduced mice, which can prey on dove chicks and likewise threaten the survival of a future free-living population. To strengthen the habitat further, more than 100 seedlings of four endemic tree species have been planted since 2016. This reforestation forms the basis for preserving the native flora and provides the Socorro dove and other species with new refuges and food sources.

The Socorro dove plays a crucial role in ecological balance, because as a seed disperser it ensures the natural regeneration of vegetation. It is precisely this function that it will perform in the restored ecosystem, thus contributing to the island’s long-term stability. But other endemic species such as the Socorro mockingbird (Mimus graysoni) also benefit from the restoration. Accompanying studies on genetics, disease susceptibility, and possible hybridization are also intended to help minimize risks for the remaining dove population in human care and for future releases. The progress so far is promising, but the Socorro dove still requires comprehensive protection in order to avoid a fate like that of the extinct passenger pigeon or the Carolina parakeet.

Plan for reintroducing the Socorro dove

The aim is to release breeding birds step by step as soon as the island is largely free of invasive predators and herbivores and offers sufficient vegetation, nesting opportunities, and food. Initial returns from the European breeding program were already planned for 2005, but failed because of import and permit problems.

To be prepared for possible setbacks, a reserve population in the USA was established in 2008, which can be transferred back to Mexico if necessary. At present, institutions around the world are cooperating within the framework of the Socorro Dove Project to create the logistical, legal, and ecological requirements for a successful release.

Can reintroduction succeed?

Although the Socorro dove has disappeared from the wild since the 1970s and therefore faces enormous challenges, coordinated efforts are under way to prepare for a possible reintroduction. A major focus is on ecosystem restoration, which has already begun: invasive sheep and cats are being removed as far as possible, and targeted reforestation is recreating a habitat in which the doves could survive in the long term.

At the same time, breeding in human care is at the center of these efforts. Despite the small population size, the Socorro dove still has a sufficiently diverse genetic basis to allow a small, stable population. Experience from other projects is also encouraging: in conservation practice there have been and still are examples in which bird species could be reintroduced after successful predator removal or habitat restoration—for example various rail species on small Pacific islands.

However, critical voices are also being heard. Some consider a reintroduction on Socorro impossible because the island has meanwhile been colonized by mourning doves and because mice, feral cats, and pigs still pose a threat to the Socorro dove. The fact is that such a return can succeed only if invasive predators are consistently removed or at least controlled and, at the same time, a sufficient population of pure Socorro doves can be maintained in human care.

To some experts, a return therefore still seems unlikely, but the intensive breeding efforts and ongoing habitat restoration are nurturing cautious optimism. The example of the Socorro dove makes clear how important consistent and long-term conservation measures are to prevent the extinction of more species. With sufficient patience, resources, and political will, it could one day truly become part of the island ecosystem again.

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