Birds from the Azores: An updated list with some comments on species distribution

Abstract Background An updated checklist of the Birds of the Azores is presented based on information compiled from Rodrigues et al. (2010) and from the websites, Azores Bird Club. (2014), Aves dos Açores (2014) Azores Bird Sightings (2014) and Vittery (2014), since 2010. New information The checklist has a total of 414 species, including 38 new species. Almost half of the species and subspecies that occur in the Azores have a Palearctic origin, the remaining ones being essentialy Nearctic and Holarctic species. São Miguel is the island with the highest number of bird species, followed by Terceira, Corvo and Flores islands.


Introduction
Birds (Vertebrata: Aves) are some of the most iconic animals. They play important roles in the ecosystem, and since they are abundant and diverse in most urban and rural areas, humans have established a good long-lasting relationship with them (e.g., birdwatching, photography). However, amongst the ca 10.000 bird species which have been living on Earth since the appearance of modern humans, many species were regionally lost or extinct, or are endangered, especially on islands (Sax et al. 2002, Elphick et al. 2010, Rando et al. 2013, Alcover et al. 2015. Updating a list of birds from remote oceanic islands represents an important step towards an improved knowledge of colonization mechanisms and migratory patterns by animals and a contribution towards the conservation and management of insular taxa and their natural habitats. The Azores Archipelago is located in the North Atlantic Ocean, between 36°55' and 39°4 3' N, and 24°46' and 31°16' W, about 1500 km from mainland Europe and 1900 km from North America (Fig. 1). The Azores is a volcanic oceanic archipelago consisting of nine islands and several islets of recent volcanic origin (0.25 to 8.12 My old), which are spread over >600 km along a northwest-southeast transect (França et al. 2003). The oceanic distribution of these islands and, as a consequence, their relative positions, has led to the formation of the following groups: (i), a western group, comprising the islands of Flores and Corvo; (ii), a central group, with the islands of Faial, Pico, São Jorge, Terceira and Graciosa and (iii), an eastern group, made up of the islands of São Miguel and Santa Maria.
Due to its remoteness, the Azores archipelago was discovered and humans settled only at the beginning of the fifteenth century. The settlers described the islands as covered by dense native vegetation, with countless birds, especially seabirds (Frutuoso 2005a, Frutuoso 2005b, Frutuoso 2005c. Until then the archipelago was definitely a bird paradise, not only for seabirds that could use the vast coastal cliffs of the islands and islets to breed, but also for terrestrial birds which were widespread in the lush Azorean forests (Rodrigues and Cunha 2012). After human colonization started in 1439, several bird species suffered a sudden decrease in population size due to their use as food and oil source for human consumption, as well as to the introduction of predators and the destruction of their habitat . As a consequence of the human impact, six flightless bird species are confirmed to be extinct in the Azores, namely one Otus species (Rando et al. 2013) and five Rallus species (Alcover et al. 2015), but recent findings indicate that many more will be described soon (Josep Alcover and Juan Rando, pers. comm.).
Despite the reduction of several bird populations, the Azores remain of great interest for ornithologists and are considered as one of the most popular destinations for European birdwatchers (Pereira 2010, Rodrigues and Michielsen 2010), all the more since they hold two endemic species: the Azores Bullfinch (Pyrrhula murina Godman, 1866) (Fig. 2), and Monteiro's Storm Petrel (Oceanodroma monteiroi Bolton et al. 2008) (Fig. 3), and 11 endemic subspecies. Besides, the Azores archipelago displays colonies of several seabird species of great importance in the European context, and it is also possible to observe pelagic birds and a large variety of migratory birds, some of which are very rare Nearctic vagrants to the western Palearctic Michielsen 2010, Barreiros et al. 2014).  Birds from the Azores: An updated list with some comments on species distribution Rodrigues and Cunha (2011) resumed the ornithological history of the Azores, from the beginning of human settlement until recently, and the latest checklist of birds from the Azores archipelago was published in 2010 by Rodrigues et al., as part of the complete list of Azorean biota published by Borges et al. (2010). This list was based on an exhaustive review of the published literature (e.g., Le Grand 1993, Monteiro et al. 1996, Monteiro et al. 1999, Elias et al. 2006, Bried et al. 2007, Jara et al. 2008, Bolton et al. 2008, Imber 2008, Vittery 2014 but also on unpublished data following Rodebrand (2010) and Rodebrand S. & The Birding Azores Team (2010). This checklist totalled 384 species, distributed between three categories: breeding, non-breeding and potentially breeding (species reported as introduced and/or escapes from captivity and for which suitable nesting conditions exist in the Azores, but whose numbers are insufficient to allow the maintenance of self-sustaining populations in this archipelago). During the last years, and due to the growing interest of birdwatchers in the Azores avifauna, several dedicated websites have been developed, such as ABC -Azores Bird Club. (2014) (formerly Birding Azores) (http://www. birdingazores.com/), AdA -Aves dos Açores (2014) (http://azores.avesdeportugal.info/) and ABS -Azores Bird Sightings (2014) (http://azoresbs.weebly.com/ from January 2012 to February 2014 and http://azoresbirdsightings.blogspot.co.uk/ from August 2014 onward). These websites are presently used by birdwatchers as a tool to register new information about species occurrence and distribution in the Azores.
The present paper updates the previous checklist , with respect to species distribution within the archipelago and also by including new species to the archipelago. The updating is based on the sightings reports available on the websites mentioned above. We also perform a nomenclatural review of the Orders, Families, Species and Subspecies, following the 2014 IOC World Bird list (v 4.3) (Gill and Donsker 2015) published by the International Ornithologists' Union (available at http://www. worldbirdnames.org/). Some additional notes on the distribution of the different species among the islands and their biogeographic origin are presented.

Materials and methods
Based on , we completed a full taxonomic revision using the IOC Bird list (Gill and Donsker 2015) as a reference to identify the changes which occurred in the taxonomic hierarchy and synonymies. Then, we updated the list of the species recorded in the Azores archipelago until the end of 2014, as well as their distribution within the archipelago. The species newly reported for the Azores are signalled as NSR (New Species Record). Most of these NSRs were reported after 2010, but there are also a few missing records prior to this date. The species previously reported by , but whose distribution has changed since then, are signalled with an asterisk (*).
All the new information about species occurrence and distribution was compiled based on the birdwatching websites mentioned earlier, and relies on a large number of birdwatcher contributions.
In order to make the data easier to consult, the main checklist (Checklist 1) includes all the breeding and non-breeding species together, including the escapes and/or introduced species which already have feral populations in the Azores. All the other escapes and/or introduced species were excluded from the main list, and can be consulted in Checklist 2.
We considered the species with five our less records, in Azores, as Rare Species. This species are presented in a table (Suppl. material 3) with the number of sightings, number of individual recorded, and some notes.
Besides the taxonomical information and the distribution among the Azorean islands ( Fig.  4), we include information on: i) biogeographical origin, based on (Lomolino et al. 2010); ii) breeding status; iii) islands where breeding has been documented and iv) current protection status of the species according to the Azorean Decree DLR n.° 15/2012/A Governo dos Açores (2012) from 2nd April 2012, which transposes the European Directives (Birds), Conventions (Bern and OSPAR), Agreements (AEWA) and specific regional protection statuses (TOP100) to the regional legislation. The protection statuses are represented by a letter or code (corresponding to the directive, convention or law) and by a Roman numeral (corresponding to the annex) as follows:

Analysis
The updated list of the bird species recorded in the Azores comprised 38 newly recorded species, increasing the total number of recorded species and subspecies to 414. These 414 taxa belong to 24 orders, 67 families, 202 genera and 404 species. Some of the species and genus names from the previous list were changed and some families were moved to other orders. The taxonomic revision results in the addition of four new orders to the checklist.
Almost half of the species and subspecies that occur in the Azores come from the Palearctic (n = 195, that is, 47% of spp and sspp) but the Nearctic is also well represented (n = 125 i.e., 30% of spp and sspp). The species and subspecies of Holarctic origin totalled 68 (i.e., 17% of spp and sspp) (Fig. 5). The Passeriformes (songbirds), Charadriiformes (waders, skuas, gulls, terns and auks) and Anseriformes (swans, geese and ducks) are by far the most represented orders with 129, 111 and 42 taxa, respectively.

Discussion
The most striking feature of this checklist is that it shows not only an impressive increase in the number of new species records for the Azores (36, that is, plus 8,7% in less than five years), but also an enlargement of the distribution of several species among the different Azorean islands. A simple explanation for this could be the increase in the number of observers performing birdwatching out of the "high season" (autumn and spring) for vagrant birds, and possibly also the creation of the "Aves dos Açores" website, whose aim is to provide information about all common species and also about rarities, even though is mostly aimed at a non-birdwatcher public.
The situation of the Azores in the middle of the North Atlantic makes these islands a safe place for the birds taken away from their normal migratory routes by strong winds or by changes in wind direction (vagrants) (Liechti 2006). Vagrant birds have been observed using trans-oceanic ships to rest until they detect a landmass at close range and usually fly towards it (Lees and Gilroy 2009). The higher number of Nearctic species reported on Corvo Island could be related to the relative proximity of this island to the American continent, allowing birds to wander into it. Another explanation for this may be the combination of a very small area (17 km2) and the high observation pressure during the autumn, when several tens of birdwatchers visit the island. On the opposite side of the archipelago, Santa Maria Island, the closest island to the European continent, holds a higher proportion of Palearctic species. The comparatively low number of non-breeding Biogeographical origin of the species present in Azores archipelago; "Other" -marine regions (Indo-Pacific; Southern Atlantic; Sub-Antarctic; Antarctic; Tropical Atlantic) (Suppl. material 2). species observed on Graciosa and São Jorge islands may be explained, at least partly, by a lower observation pressure than on the other islands.
The native birds from the Azores provide good examples of insular speciation, since two endemic species and 11 endemic subspecies are known. Moreover, many more endemic terrestrial species have gone extinct (Rando et al. 2013, Alcover et al. 2015, possibly as a consequence of direct predation by man, the introduction of non-native predatory species (e.g., cats, rats, ferrets and weasels), and habitat degradation or loss. The current endemic species and subspecies are the survivors of almost 600 years of human occupation and major land-use changes. The recent population recovery of the Azores Bullfinch (Fig. 2) in the north-eastern part of São Miguel is considered as a good example of the best practices of LIFE conservation programs (Ceia et al. 2010). Another example of successful conservation measures comes from the rabbit eradication and habitat restoration on Praia islet (Graciosa Island), which resulted in a significant increase in the breeding numbers of Monteiro's Storm-petrels, Madeiran Storm-petrels and terns (Bolton et al. 2004, Bried et al. 2009, Bried andNeves in press).
Species lists such as this one are important to draw attention to particular taxonomic groups, to serve as a baseline in long-term systematic monitoring, to elucidate patterns of species diversity and distribution, to elucidate information gaps about distribution, and can serve as a tool in educational projects. The currently ongoing initiatives concerning citizen ornithological science in the Azores will be of high value for the knowledge of the biology and phenology of migratory birds and will hopefully increase the pressure towards the definition and preservation of more Important Bird Areas (IBAs) in the archipelago.