What happened to the Bahama Nuthatch?

On January 6-10, CCSD scientist Leighton Reid joined Bert Harris, Kelly Farrell, and David Wilcove on a search for what has become one of the rarest bird species in the western hemisphere.

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Grand Bahama Island, only known home of the Bahama Nuthatch.

The Bahama Nuthatch (Sitta insularis) is or was a bird found nowhere except on Grand Bahama Island, a thin, 153-km long piece of weathered limestone lying 84 km east of Palm Beach, Florida.

 

The Bahama Nuthatch differs from a widespread southeastern US species, the Brown-headed Nuthatch (S. pusilla) in having a longer bill and a distinctive, high-pitched warbling call. It is a denizen of the Caribbean pine (Pinus caribaea) forests that cover about 60,000 ha of Grand Bahama Island. Perhaps always rare, the species was a lot more common in the 1960s than 30 years later in the early 1990s. Ten years ago, a nearly island-wide survey found only 14 individuals in a single tract of forest east of Freeport, the island’s largest settlement. A local nature guide, Erika Gates, regularly found one to three individuals of the species in this area through June 2016, but in early October 2016, Hurricane Matthew (Category 5) blew across the island, causing significant damage. The Bahama Nuthatch has not been detected since June 2016 despite Ms. Gates and others searching in its previous locations. It is considered “endangered” by the IUCN.

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A postage stamp sheet commemorating the Bahama Nuthatch (Sitta insularis), an extremely rare species known only from a single island in the Bahamas.

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Bert Harris plays the distinctive warbling call of the Bahama Nuthatch through a speaker into a very quiet Caribbean pine forest.

For six days in early January, four of us intensively searched the area around the two most recent sightings, the ones from May and June 2016. We focused on the core area at first and gradually expanded outwards as it became clear that we were finding no individuals at the former sites. We estimated that we searched an area of roughly 4600 hectares of pine forest over a period of 26 hours (88 person-hours). We travelled approximately 92 km of roads and trails, both driving and walking. Many of these were old logging roads, which crisscross the entire island. While driving, we stopped every 0.4 km (0.25 mi) and played a recording of the nuthatch’s distinctive call. While walking, we played the call more frequently.

We did not find any Bahama Nuthatches. We think that our group, the first to search for multiple days for this species since 2016, was also the first to fail to find it. Perhaps the species’ conservation status should be changed from endangered to critically endangered. Ideally, some Bahamian ornithologist will be able to survey again for the species during the coming breeding season, and if the species is rediscovered, its remaining habitat will be protected, restored, and expanded.

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In addition to the Bahama Nuthatch, we noted that several birds which breed exclusively in the pine forests were also very rare or absent. Bahama Yellowthroats (Geothlypis rostrata), Bahama Warblers (Setophaga flavescens), and Olive-capped Warblers (S. pityophila) were relatively abundant during surveys in 1968 and 2007, but Bahama Yellowthroats were totally absent from our search, and we found only a handful of Bahama Warblers and Olive-capped Warblers, making them even rarer in our survey than the nuthatch was in 2007 (though we searched during some relatively cold weather and during the non-breeding season). We also failed to detect a single Bahama Swallow (Tachycineta cyaneoviridis). Looking through historical records on eBird we noted that the West Indian Woodpecker (Melanerpes superciliaris) was formerly abundant across the island but has not been recently seen.

The causes of decline for the Bahama Nuthatch and perhaps for other breeding birds of the pine forests are mysterious. Grand Bahama Island has been extensively logged, initially for large diameter timber (prior to 1900) and later (1940s-1970s) for pulpwood. The expansion of the city of Freeport and tree-killing inundation by seawater over large areas have both reduced the potential habitat area. Feral cats, introduced raccoons, and corn snakes introduced in the 1990s could be predating native birds. We saw at least nine raccoons during our short time on Grand Bahama. Altered fire frequency and the increased frequency of Atlantic hurricanes may also be impacting the species, possibly by removing snags that are required for nesting.

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As recently as 2011, 65 Caribbean ornithologists were able to view the Bahama Nuthatch simultaneously and within three meters of a tour van. Photo by Erika Gates.

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Guadalupe Island, Baja California: Invasive mammal eradication and perspectives for ecological restoration

James and Thibaud Aronson are working on a book, with James’s longtime collaborator Edouard Le Floc’h, on “desert canopies” and ecological restoration in arid and semi-arid regions of the world. They report here on the first leg of their trip to Baja California, Mexico.

Isla Guadalupe is a large volcanic island (250 km²), 240 km west of northern Mexico, with fewer than 150 permanent inhabitants. Approximately one-fifth of the island’s 150 native plant species are endemic. Of particular interest are the remnant populations of trees in the foggy, northern highlands of the island, including an endemic variety of Monterey pine (Pinus radiata var. binata), and the endemic cypress.

Guadalupe cypress (Hersperocyparis guadalupensis) in the “sky island” on the central highlands of the island.

Guadalupe cypress (Hesperocyparis guadalupensis) in the “sky island” on the central highlands of the island.

Three additional tree species survive in small populations : an endemic oak (Quercus tomentella), California juniper (Juniperus californica) and an endemic fan palm (Brahea edulis). At the southern end, there are remnants of both chapparal and matorral shrublands including taxa with Californian affinities and others from the Sonoran desert biome. The southern tip is very dry – with just 120 mm (5 in.) of mean annual rainfall. The northern half is mountainous with 250 mm (10 in.) of annual rain, and thick fogs that double or triple the effective precipitation.

People first came to the island in the early 19th century. By 1850, sailors had introduced goats to provide a meat reserve for passing ships. Not surprisingly, the goat population exploded, reaching an estimated 100,000 animals by 1870. Over-grazing led to the disappearance of entire plant communities and several dozen endemic species. One example is Hesperelaea palmeri, an endemic member of the olive family. Particularly appreciated by goats, it was gone by 1870. Domestic cats got to the island somewhat later, probably introduced intentionally to control the mice. The cats went feral, and had an enormous impact on the extremely tame birds, both endemic land birds, and breeding seabirds.

By the early 20th century, 6 of the 9 endemic land birds had gone extinct, as well as an endemic seabird. Meanwhile, the Guadalupe fur seal and the northern elephant seal were hunted relentlessly, the former for its fur, the latter for its blubber. The hunting only stopped in 1894, when both species were thought to be extinct. Happily, both species did in fact survive, albeit in extremely small numbers; the entire fur seal population dropped to 15 individuals. In 1928, the island became a set-aside reserve and seal populations finally started to recover, and today, they number 20,000!

Fur seal (Arctocephalus townsendi) on Isla Guadalupe, March, 2015.

Fur seal (Arctocephalus townsendi) on Isla Guadalupe, March, 2015.

The northern elephant seals have done even better. They have recolonized much of the northern Pacific, and the total population is more than 150,000 individuals.

Elephant seal (Mirounga angustirostris) on Isla Guadalupe, March, 2015.

Elephant seal (Mirounga angustirostris) on Isla Guadalupe, March, 2015.

On land, however, things kept worsening. The goat numbers stabilized around 15,000. As a result of over-grazing, most of the island was stripped to bare soil and rocks; only a few hundred trees survived and goats ate every seedling they produced. Cats caused enormous mortality in breeding seabirds and one of the remaining three endemic land birds, the Guadalupe Junco (Junco insularis), was headed towards extinction, with only 50-100 individuals left.

That’s when the Group for Ecology and Island Conservation (GECI) got in gear, and it’s thanks to them that things are looking up. Since 1995, this NGO has eradicated 48 populations of invasive mammals – mostly sheep, goats, cats, and mice – on 30 Mexican islands. They got to Guadalupe in 2002 and started an intensive eradication campaign. By 2007, the goats were gone. Within a year, the trees had produced thousands of recruits, which today are several meters high, in the case of both the pine and the cypress. In fact, in 2008, a fire burned through a large portion of the remaining stand of cypress. A few years earlier, this would have been a catastrophe. But without goats to eat them, thousands of seedlings sprouted immediately all over the burnt area and are growing nicely, thanks not only to the absence of goats, but also  to the heavy fogs, which provide favorable conditions for the seedlings. Besides, half a dozen native shrubs, including some endemic species, have reappeared in large numbers  in many parts of the island. Several species which were though extinct have been rediscovered, and one new species has been discovered as well.

All is not well, however, in the invasives department, nor in soil conservation. Dozens of species of herbs and grasses from the Mediterranean Basin and Europe are prevalent in open areas, and there are dramatic signs of soil erosion. Former shrublands – matorral and chaparral – are deeply degraded everywhere on the island. Half a dozen species of native shrubs are re-colonizing certain areas and acting as very effective pioneer species. These are being watched and probably can be used in active restoration efforts in the future.

Feral cats and several kinds of mice are still present and continue to prey on birds. However, a fence now protects the southern tip of the island, which is home to a breeding colony of the Laysan albatross, one of few albatross populations in the world which is growing in numbers.

Laysan albatross (Phoebastria immutabilis) breeding and raising chicks on Isla Guadalupe.

Laysan albatross (Phoebastria immutabilis) breeding and raising chicks on Isla Guadalupe.

Laysan albatross

To date, GECI has focused on eradicating invasive mammals, mainly to protect marine birds. The regeneration of the island’s vegetation was a happy by-product. However, they are now seeing the potential for taking a more active hand in restoring the islands’ plant communities. We suggested several approaches. One would be the establishment of plant nurseries to support both ex-situ conservation and reintroduction of plants within experimental plots set up to study what approaches are most effective for different plants, in different parts of the island. There are only 30 to 40 adult oak trees left on the island and less than 10 known Junipers. Unlike the endemic cypress, pine, and fan palm, neither the oak nor the juniper is recovering. Active intervention will be needed to reconstitute mixed conifer-oak woodlands and to bring the fan palm populations back to their former glory. Finally, some heavy work is needed in relation to water and soil management, and roughly 400 feral domestic cats still run free on the island. Total eradication will be extremely costly, but GECI hopes to achieve it by 2025. As is the case in Madagascar, and Sri Lanka, restorationists must learn how to cope with and manage fire.

With all this in mind, can our friends from GECI initiate a sustainable restoration process on the entire island, ideally within a coherent conservation, management, and restoration plan? Also, can the restoration work underway serve as a prototype for restoration on other islands, e.g., Mauritius and Madagascar where MBG scientists are already working?

Spontaneous Guadalupe cypress regeneration following the fire of 2008.

Spontaneous Guadalupe cypress regeneration following the fire of 2008.