Species Endangered (MS-Blog Series from) - III / 09

Bermuda Petrel

• Class: Avia
• Order: Procellariiformes
• Latin name: Pterodroma cahow
• Range: Bermudan Islands
  

• IUCN Status : EN (Endangered) /
• CITES: Not listed (Marine species usually aren't)
• (above a 2008 situation)
  

For centuries supposed an extinct species, Bermuda Petrel (Pterodroma cahow) in some ways resembles one of the frog species (Mallorcan Midwife toad) mentioned in our previous post. Bermuda Petrel was also quite recently found having survived to our times, and has been protected since. The recovery of bird(s) has also been supported with conservation efforts. The story of the Bermuda Petrel is rather famous, but because we're not too familiar with it and it's general popular renown goes back some decades, it's included as next in the series.

Endemic to Bermudan Islands solely, Bermuda P. is counted in gadfly petrels. The upper main order, Procellariiformes contains basically petrels, sometimes also Albatrosses (Diomedeidae) are included within. Other co-families (in that taxonomy) are the Storm Petrels (Hydrobatidae), and Diving-petrels (Pelanoides). The remaining family Procellariids contains the gadfly petrels in addition to some other sub-groups (or about so, I would guess these aren't always that clear/permanent and sometimes the species classifications are changed).

Petrels feed at open sea and are pelagic marine birds (mostly?). In common image petrels have been called the storm birds, due that they are excellent fliers and seem to be almost 'safe at home' in the bad weather. Typical to the petrels is also that they breed slowly, usually only one descendant in successful season, the incubation taking generally long period: In case of Bermuda Petrel for about over 50 days, but for Albatrosses that have the longest incubation time of any birds, it may be from 70 to 80 days. The fledglings leave the nest after around 13-14 weeks age, the young petrels usually returning to the breeding islands when having reached mature age, in about 4 to 5 years. Petrels only spend part of the year in the nests, their breeding period, which also includes the period of parental watch for newborn chicks. Most part of the year they spend on open seas in search of food, practically being dependable on sea fish.

In spite of some successes in recent decades, species population growth for a more stable level has taken about half the century. And basically it's listed as EN because the population has been noticed at slow but stable increase; any sudden change for the worse could immediately turn that to downwards trend, the species being classified critically endangered, CR. Byrds numbers were (2005) just around the 250, often used as some number (/level of criteria) in those classifications. On the other hand, further continued population growth would possibly mean downlisting in the IUCN classification. [But, as we've learned in during these discussions, population numbers usually tell but half the truth, animal populations concerned and even abundant species can quickly become endangered if the habitat is destroyed, or species other ways largely hunted, harmed, etc)]


Whatever one thinks the fitting classification in Petrels case, that's way down from the estimates of the byrds frequency prior human arrival/affect (no reason to suspect those numbers, though the amount is probably difficult to ensure with certainty). It was once 'superabundant', supposedly had a population of about 500 000 individual specimen. Bermuda Petrel becoming endangered and supposed as extinct, like was the belief for over 300 years, has its origins in the times of explorers/travelers arriving its home island. Not any way unusual a story, like we can notice from following paragraphs. The rediscovery is more atypical one and soon became a symbol for hope in concerning the threatened bird species in general and the marine birds in particular. But for the record it can also be mentioned that at least one other species of Petrels was supposed to be extinct for a long time, about 150 years, until in 2003 it was also rediscovered.


There's also lot variation in amounts of populations in between different recognized (Petrel) bird species. Some belong to most numerous from sea birds like Wilson's Storm Petrel (Oceanites Oceanicus) and Short-tailed Shearwater (Puffinus tenuirostris), which both are counted in numbers over tens of millions – but some are so rare that even their nesting sites are still nowadays not known. Fx, Fiji Petrel is mentioned having been seen for only handful of times after it was identified as particular species. Only in Bermuda's petrel's own Pterodroma genus there's number of (pelagic) species which are known to be severely threatened, fx: Chatham Islands petrel (P. axillaris, CR) ; Galápagos petrel (P. phaeopygia, CR) ; Jamaica petrel (P. Caribbaea, CR - possibly extinct) ; Black-capped petrel (P. hasitata, EN) ; Barau's petrel (P. baraui, EN) ; Trindade Petrel (P. arminjoniana, VU) ; Atlantic petrel (P. incerta, VU) ; Murphy's petrel (P. ultima, NT)². Since for the Procellariidaes in addition to gadfly petrels also are counted the shearwater-, fulmarine petrels and prions families, these likely contain several more threatened species, though we don't go listing those more especially here.


But, we can now here re-read (part) of the Bermuda P. story to get the better picture; the human caused impact on birds survival began when early Spanish sea-farers in 16^th century began leaving hogs grazing in wild on island and that way using the place as living food store for passing ships (superstitious from the nocturnal voices of birds on island, they were not building any permanent settlements on islands). A bit later, the actual disappearance of of the species would nevertheless have happened in rather brief period of time, in only about 10 to 15 years as can be read from the following citation:

Lost and found. Bermuda remained uninhabited until 1609, when an English expedition was shipwrecked there. At the time the islands were teemed with seabirds, including vast numbers of Bermuda petrels. Soon, however, settlers arrived in force, bringing with them pigs, rats, and other animals that raided the petrels' nesting burrows. To make matters worse, the settlers themselves also caught and ate huge numbers of the birds, until by 1621 the species was thought to be extinct.

No specimen were recorded for more than 300 years, but then, miraculously, the bird turned up again. The first clue of existence came in 1906, when a dead petrel was found an Castle Island, one of the smallest in Bermuda. At first it was taken to be a previously unknown capped petrel from the Caribbean region, but then in 1916 another individual turned up – and it seemed to fit the 17^th century descriptions of the missing species. The clinching record came in 1931, when a bird that hit St. David's lighthouse was retrieved and identified as Bermuda Petrel. Another definite record was of an individual that struck a telephone pole in St. George, at the northeastern end of the main island.

The puzzle of where these birds came from remained, since none could be found nesting on any of the inhabited islands. In 1951 a search turned up 18 pairs of the petrels on rocky islets in Castle Harbor, near St. George. The total area of these islets was only 2.4 acres (1 ha). Instead of nesting in burrows as they had done in the 17^th century, the petrels were now using natural crevices created by water erosion of the soft limestone rock, since there was little soil on the islets.” ¹

Often marine and other birds of islands have gotten endangered similar way as the Bermuda petrels described above. That may not always have happened such quickly, but following the arrival of human settlement on their living islands. The popularly known examples from the extinct birds are probably Dodo and Moa, that also disappeared directly of human impact (overhunting) and/or indirectly as result from human brought co-threats. In the various islands on seas, that usually have served as nesting sites for large number of marine birds, there's examples more similar to Bermuda P. case.


A typical example, St. Helena's Island in South Atlantic (also renown as the place where Napoleon was finally exiled and later died at early 19^th century), is a more striking one, since from the island in addition to two native sea-water species(St. Helena's Small and Large petrel - Bulweria bifax and Pterodroma rupiram), also main part from the unique terrestrial endemic byrd species disappeared. And, again (largely) because of the above mentioned various threats humans brought along with themselves, the new alien species - cats, rats and pigs. In the pelagic islands where species originally lack such native predators, introduced pets and domestic animals were often been found a more severe threat to native bird species than any other human caused things.


Sometimes the foreign species have been brought to islands unintentionally or for the uses of farming as pest killers. Concerning the pelagic byrds fx, there's Brown tree snake – apparently by accident brought to Guam (at Pacific Ocean) where it killed most from islands native bird population. Another comparable example from human brought invasive species - if not expecially for birds - is Cane Toad (Bufo Marinus) that mainly in the 1930s was introduced for various Pacific and Caribbean islands as elsewhere too (with the intention to dispose the beetles in sugar cane farms.) Toad has certain toxins and so in addition to appearing mainly a failure in its original purpose as biological control agent, the Cane Toads were also often found a threat for several native species (in general, the toad more usually turned out to be a pest itself affecting various native animals populations in host countries - For further information about the past history, consequences and failures of that 'Great Cane Toad pest killer Experiment' , one can read this informative article from Cane toads in Australia (One can check the more recent information/news on Cane toads, too.) It is estimated that world-wide large part (80 per cent) from endangered species suffer from human introduced (intentionally or non-intentionally) competitors or predators. Some may date back in the prehistoric times, some are newer cases.


Also, fx nowadays in the Hawaii native birds are often mentioned among the most endangered; from the islands current species over 40 per cent is by origin not native, but brought by humans. From the land birds the introduced species comprise 69 per cent from the total. Hawaii is to some point an exceptional case since the islands environments, rich with plant and vegetation, as well as the animals had remained in isolation for millions of years. More recently human invasion, (supposedly) first the Polynesians and later in the 19th century European settlers arriving for the Hawaii archipelago both caused new invasive species to spread for the islands original environments (and also some time closer to our days, more intensive deforestation and farming). As result many from native birds are found to habitat only in the higher elevations, likely the mountain-sides. (Nowadays Climate Change is also expected to reduce those safe environments.)

Several albatross species like the Black-footed Albatross (Phoebastria nigripes) that breeds on some North-Pacific islands including Hawaii, have also recently become endangered much because of long-lining fishery (in during 1978-1991, especially when there probably wasn't any level of regulations for that). Having somewhat strengthened in their numbers during the 2oth century (earlier decline's is often attributed to common human practise as well, feather and egg collecting in 1800's and early 1900's), several albatross and petrel species are found still threatened by long-lining, although fisheries should utilize techniques that cause less seabird by-catch. As well, there's nowadays nets more 'safer' to birds, though their use is of course been found less easy to guarantee/control. In 1991 was established a protected species zone where no long-line fishing is allowed (for about 50 nautical miles to the North-western oceans from Hawaii). But, the fisheries by-catch nevertheless still causes unnecessary deaths for many albatross and petrel specimen yearly, and plenty of species are affected.


One of course can remark that recently also more common (bird) species worldwide were observed in decline (though several from those are also capable to recover more quickly, perhaps.). But returning to petrels, amongst marine birds, they are with albatrosses most severely threatened taxa worldwide, though only one species is mentioned confirmed to have gone extinct since the 17th century - That is Guadalupe Storm-Petrel (Oceanodroma macrodactyla), which disappeared in the early 20^th century, mostly because of non-native predators on its home island (cats). Various other species are vulnerable since their populations have diminished and/or have not been seen for some time.


Since Bermuda petrels have been protected from 1950s their amount has been slowly in raise with the help of conservationist effort. These have included protection from some competive tropical bird species as well as prevention of rats to reach the birds nesting sites. Other threats for species include fx the long-line fishing, since it not only kills large number birds still, but also effectively weakens the catch of fishes available for birds. Additionally, there's sea-waste (flotsam), general marine pollution including oil spills, and the other pollutants like DDT, noticed a reason for the failure of bird eggs to hatch. More recently, some serious flooding as result of sea level raise and a hurricane few years back caused destruction to their burrows (nest sites), so the other potential suitable environments in close islands for breeding sites have been seeked. But, their population is been now found increasing, now at about 25 per cent breeding success (from 5 per cent in 1950s).



From the variability of particular birds mentioned in this post, we can notice that it of course not mainly tells from the vast number of different (marine) bird species, but the various humans caused threats which have largely increased the number of endangered. Of course, the conservation efforts having success also tells that many species are capable to recover quickly if aided. But, like the example here, it may also take far longer period of time in cases where species is slowly reproducing and also natively limited to/breeds only in certain geographic area (like islands). In this particular case, (if wish) to determine for how long depends from perspective taken; recent limited population growth may be seen as result from last 50-60 years various conservation efforts, but as the actual disappearance only took some decades the recovery can also be seen having been some 300-400 years process.

Notes:
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1. Beer-Morris, 2005, The encyclopedia of Endangered Animals.[Bermuda Petrel]

2. (These related endangered) species are listed in the book (see the note 1 above).



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