AÇOREANA, Suplemento 6, Setembro 2009: 217-225

A CONSERVATIONAL APPROACH ON THE SEABIRD POPULATIONS OF ILHÉU DE VILA FRANCA DO CAMPO, ,

Pedro Rodrigues1, Joana Micael1, Roshan K. Rodrigo2 & Regina T. Cunha1

1 CIBIO-Pólo Açores, Department of Biology, University of the Azores, 9501-801 , São Miguel, Azores, Portugal. e-mail: [email protected] 2 Faculty of Science, Department of Zoology, University of Colombo, Colombo 7, Sri Lanka

ABSTRACT This study was performed to identify the seabird species occurring on Ilhéu de Vila Franca do Campo (IVFC) off São Miguel island, Azores, giving a special emphasis on the description of their ecology and threats. Flush counts, ground searches and raft counts were conducted and two types of natural habitats were identified. The results confirmed the nesting of two and revealed three other possible breeders enhanc- ing the importance of the islet for the protection and conservation of Azorean seabird pop- ulations. Although playing an important role on the conservation of Cory’s shearwater and Common tern populations, the islet can be threatened by continuous habitat degra- dation by human disturbance. The implementation of a habitat restoration program is suggested for the islet in a near future.

RESUMO Foi feito um levantamento das espécies de aves marinhas que ocorrem no Ilhéu de Vila Franca do Campo, com especial ênfase para a sua ecologia e ameaças. Foram realizadas contagens visuais, procura de ninhos e contagem de jangadas ao longo de todo o ilhéu e zonas adjacentes, confirmando a nidificação de duas espécies ameaçadas e a possibilidade de nidificação de outras três. A identificação de dois tipos de habitats naturais evidencia a importância do ilhéu para a protecção e conservação das populações de aves marinhas. Apesar do importante papel na conservação das populações de cagarros e garajaus- comuns, o ilhéu de Vila Franca do Campo continua a ser ameaçado por uma contínua degradação dos seus habitats devido à acção humana. Este trabalho sugere, num futuro próximo, a implementação de medidas proteccionistas e um programa de restauração dos habitats naturais deste ilhéu.

INTRODUCTION borealis), Manx shearwater (Puffinus puffi- nus), Little shearwater (Puffinus baroli), he Azorean archipelago, located in the Band-rumped storm-petrel (Oceanodroma Tnorth Atlantic Ocean, has always been castro), Monteiro’s storm petrel recognized as an interesting place for (Oceanodroma monteiroi), Yellow-legged birds, mainly seabirds, not only due to the gull (Larus michaelis atlantis), Common coast line with steep scarps but also to its tern (Sterna hirundo) and Roseate tern (S. geographical location (N36-39º, W25-31º) dougallii). There are two occasional that represents an ornithological transi- breeders, Red-billed tropicbird (Phaethon tion between temperate and tropical aethereus) and Sooty tern (Onychoprion fus- zones (Monteiro et al., 1996a, b). catus), a possible breeder, Cape Verde Thirteen seabird species are known to petrel (Pterodroma feae), and a possible for- occur in the Azores. The regular breeders mer breeder, White-faced storm-petrel are Bulwer’s petrel (Bulweria bulwerii), (Pelagodroma marina) (Le Grand et al., Cory’s shearwater (Calonectris diomedia 1984; Monteiro et al., 1996a). 218 AÇOREANA 2009, Sup. 6: 217-225

The archipelago accounts for the around 2000 couples (5% of the European largest population of Cory’s shearwater of population) (Rodrigues & Nunes, 2002). the world with more than 180.000 couples All these seabird species have a vul- (79% of the European population) nerable status, except Roseate tern which (Rodrigues & Nunes, 2002). Also repre- is in Danger, and the Common tern with a sentative are the populations of Band- Favourable Conservation status rumped storm-petrel, 915 to 1240 couples (Rodrigues & Nunes, 2002). (around 25% of the European popula- Most seabird populations breeding in tion), Little shearwater, 800 to 1500 cou- Azores have been suffering dramatic his- ples (around 20% of the European popu- torical declines as a consequence of major lation) (Monteiro et al., 1999), Roseate tern habitat degradation, mainly by human with more than 1000 couples (60% of the activities from the late 15th century on, European population) and Common tern, and the introduction of mammalian

FIGURE 1. Ilhéu de Vila Franca do Campo with identified habitats, burrows and nests cavities. C - Vegetated Sea Cliffs of the Macaronesian Coasts habitat; H - Endemic Macaronesian Heaths habitat; F - Forests of iron trees; V – vineyards; + Common tern (CT) nests; * Cory’s shearwater (CS) burrows/nests cavities; CS destroyed nest; CS abandoned nest; CS abandoned egg; CT destroyed nest; CT abandoned nest; CT abandoned egg; Area of public permitted access. RODRIGUES ET AL: SEABIRD CONSERVATION AT ILHÉU DE VILA FRANCA 219 predators (Monteiro et al., 1996b), so they This study was developed to identify tend to breed on isolated islets and sea the breeding species of seabirds on IVFC, cliffs, free of predators and human distur- giving special emphasis to habitat char- bance, with natural habitats without inva- acterization and threats, thus contribut- sive alien species (Monteiro et al., 1996b; ing to the conservation and protection of Ramos et al., 1997; Groz & Pereira, 2005). the islet’s natural habitats and their One of these islets is the Ilhéu de Vila seabird populations. Franca do Campo (IVFC) (Figure 1), 1.2 km south of São Miguel island. MATERIAL AND METHODS Several studies were published on the islet’s biota, describing its general topog- The study was carried out on the raphy and biological characteristics, IVFC (N37º42.30’, W25º26.52’), during mainly about its marine life and coastal July 2006, in the course of the 3rd interna- ecology (Martins, 1978, 1995, 2004; tional Workshop on Malacology and Morton, 1990; Britton, 1995; Backeljau et Marine Biology in Vila Franca do al., 1995; Morton et al., 1998) revealing the Campo, São Miguel, Azores (Figure 1). ecological and geological importance of The islet is a drowned volcanic crater the place. with a surface area of 61.640 m2, accessed Some surveys targeting Cory’s shear- by a narrow channel, but with several water and terns were made in the Azores fissures also connecting the lagoon with (del Nevo et al., 1993; Bolton, 2001 and the sea outside. The main length of the Monteiro et al., unpublished report) but islet is 420 m from east to west, reaches none of them went to the islet. Monteiro an altitude of 62 meters, and is divided et al. (1999) estimated 0 to 10 Band- into two portions: the Big islet, that con- rumped storm-petrel couples breeding on stitutes almost all the islet’s area and the the islet. Small islet on the northeast side. There Due to the unique importance of the are also several rocks of different sizes, IVFC as an agglomeration of various outstanding the Farilhão with 32.5 m, micro-ecosystems, the Azorean and Baixa da Cozinha with 19.4 m. On Government established it as a Nature the islet there is an internal lagoon con- Reserve in 1983, as provided by the nected to the open sea trough chaps and Regional Legislative Decree nº 3/83/A, of underwater tunnels. Inside the lagoon March 3rd, and some rules were imple- there is a small pier where people enter mented with the intention to preserve the islet (Martins, 2004). and protect the islet; the public access was The habitat characterisation of the restricted to the lagoon, the marine area islet was made in loco following the of the reserve was extended to 30 m deep, Interpretation Manual of European and fishing and any underwater activity Union Habitats (European Habitats were forbidden. In spite of these protec- Committee, 1991). tion measures, the flora and fauna in the Three different methods were con- islet and its lagoon have suffered a signif- ducted to identify the seabird species of icant negative impact caused by the flood the islet, and to estimate species abun- of people mostly during the summer dance and number of breeding pairs: (Morton et al., 1998). The islet is popular 1. Flush counts for recreation and between May and Six boat rides, of 15 minutes each, September a boat brings in about 400 per- were undertaken for flush counts of sons a day. seabirds and to observe the external 220 AÇOREANA 2009, Sup. 6: 217-225 coast zone of the islet. The method con- RESULTS sisted on counting the number of indi- viduals visible from the boat (eye view), Habitats at different hours of the day, three rides Two types of natural habitats were in the morning and three on the after- identified on the IVFC (Figure 1): i) noon. Species were identified and all the Vegetated Sea Cliffs of the Macaronesian individuals standing on the islet or fly- Coasts habitat, dominated by the endem- ing over the sea were counted. ic fescue (Festuca petraea), with associat- 2. Ground searches ed such as rush (Juncus acutus), Two ground searches were made for wild carrot (Daucus carota), seaside gold- occupied nests of terns and enrod (Solidago sempervirens) and rock Porcellariiformes (Figure 1). Signs of samphire (Crithmum maritimum); ii) occupation included the presence of an Endemic Macaronesian Heaths habitat adult, eggs or chicks in a visible nest dominated by the endemic green heather chamber. In sites where a nest chamber (Erica azorica), with associated plants was not visible, a burrow was considered such as laurel (Laurus azorica), Myrica to be occupied if it was of sufficient size faya, Cyrtomium falcatum, Holcus rigidus to accommodate a bird or if there was and Euphorbia azorica. This last habitat one or more evidences of occupation presents plenty of exotic plants such as (e.g. faeces; shed breast feathers, exca- the giant reed (Arundo donax), used in the vated soil or absence of obstructing veg- past for protective barriers of the vine- etation or spider webs in the burrow’s yards, tamarisks (Tamarix gallica), bram- entrance). bles (Rubus ulmifolius) and australian pit- 3. Raft counts tosporum (Pittosporum undulatum). During the breeding season, Cory’s On the higher southern and western shearwater characteristically form flocks inner slopes of the Big islet there are two (called “rafts”) on the sea, with the num- small “forests” of iron trees (Metrosideros ber of individuals increasing by the end tomentosa) and vineyards (Vitis labrusca), of the day, waiting for nightfall to fly up although they are no longer cultivated. to the breeding colony (Mallet & Coghlan, 1964). According to Richdale Seabirds (1963) and Skira (1991) over half of the There was evidence of two species of adult shearwaters at a colony are seabirds breading on the islet (Figure 1), expected to be non-breeders. Cory’s shearwater and Common tern, Raft counts were conducted for but three more species were registered, Cory’s shearwater from two places, one Little shearwater, Band-rumped storm- on the top of the south side of the islet, petrel and Roseate tern, although at pre- and another from Ponta de São Pedro sent without any breeding evidence. (N37º42.39’, W25º26.41’) on the coast of Table 1 shows avifauna abundance São Miguel island and in front of the determined through the different meth- islet; raft counts were made by the end of ods used. the day, starting exactly at 08:00 pm, for Cory’s shearwater breeds on Big islet 45 minutes long, using binoculars (10 X with Vegetated Sea Cliffs of the 50). Macaronesian Coasts habitat where 34 All the methods applied in this study burrows and nests cavities were found, involved two replicates from two differ- and on slopes of Endemic Macaronesian ent observers. Heaths habitat that exhibited 10 burrows RODRIGUES ET AL: SEABIRD CONSERVATION AT ILHÉU DE VILA FRANCA 221

TABLE 1. Seabird abundance from flush and raft counts and number of couples from occupied nests/burrows on the Ilhéu de Vila Franca do Campo. SD = Standard Deviation. Flush counts Ground searches Raft counts (individuals) (couples) (individuals) Species Mean ± SD Mean ± SD Cory’s shearwater 154 ± 22.6 44 395 ± 21.2 Common tern 325 ± 35.4 80 - Roseate tern 2 - - Little shearwater 1 - - Band-rumped storm-petrel 1 - -

and nests cavities. The three nests found 1% of Common tern eggs were aban- on Small islet were destroyed or aban- doned by the progenitors. doned. Common terns breed on two external DISCUSSION rocks of the islet, Baixa da Cozinha (10 nests) and Farilhão (19 nests), and on the The Vegetated Sea Cliffs of the external coast of the Small islet with Macaronesian Coasts habitat of the IVFC Vegetated Sea Cliffs of the Macaronesian are well preserved probably because they Coasts habitat (41 nests). occur on the external rocks of the islet and Occasional observations on the popu- on inaccessible cliffs, but also because lations of Cory’s shearwater and they are highly influenced by salt-water Common terns allowed identification of spray where exotic plants cannot grow. chicks being reared, incubating parents, According to Sjögren (1973) the associa- destroyed and abandoned nests and tion Festucetum petreae is characteristic of abandoned eggs (Table 2). It was not pos- Azores coastal habitats, occurring mainly sible to identify the exact number of eggs in the sea cliffs. The characteristic species laid per couple of Common terns. of this association is the common endem- Evidences of human disturbance were ic Festuca petraea, which usually develops found near potential seabird nests, coastal prairies. Other species are found including recreation, wastes, and vandal- in this association, such as the common ism such as broken eggs and burrows Solidago sempervirens and Crithmum mariti- destruction. There were an equivalent mum, the less common Tolpis succulenta percentage of abandoned nests in both and even rarest endemic plants like populations (11%) and about 18% of Azorina vidalii and Myosotis maritima. Cory’s shearwater nests and 5% of The Endemic Macaronesian Heaths Common tern nests were destroyed. habitat was much degraded with exotic Nearly 7% of Cory’s shearwater eggs and plants such as Arundo donax, Lantana

TABLE 2. Number of observations on Cory’s shearwater and Common tern nests on Ilhéu de Vila Franca do Campo. Used Destroyed Abandoned Abandoned Incubating Rearing Species nests nests nests eggs couples chicks Cory’s shearwater 44 8 5 3 9 6 Common tern 80 4 9 1 37 11 222 AÇOREANA 2009, Sup. 6: 217-225 camara and Pittosporum undulatum. human disturbance is almost absent, and According to the Convention on where they can avoid possible predators. Biological Diversity, invasive alien species Adults arrive in colonies by early-April, which introduction and/or spread threat- egg laying occurs from early-May to mid- ens biological diversity are now consid- June and they stay in colonies until late- ered the second cause of biodiversity loss September (Monteiro et al., 1996b). A at a global level, after direct habitat clutch of 2-4 (usually 3) eggs is laid. One destruction (Shine et al., 2000; Groz & brood per season is typical but re-nesting Pereira, 2005). is common when the first nest is The methods used in this study to destroyed (Peterson, 1988). This study estimate species abundance and number indicates that the colony on IVFC repre- of breeding pairs were effective because sents at least 18% of the Azorean total pop- they complemented each other giving a ulation. broader view of the colonies. These Although being a protected species, results confirmed nesting of two endan- populations of these seabirds are becoming gered species and listed three other possi- smaller than in the past, they have been ble breeders revealing the importance of chased and hunted by humans, and suf- the IVFC for the protection and conserva- fered with predation from introduced tion of seabirds. mammals and from deforestation Cory’s shearwater breeds generally in (Monteiro et al., 1996b). the inaccessible sea cliffs of the islet and The suite of terns and shearwaters is of less in slopes with Macaronesian vegeta- major international conservation tion. The differences between the num- importance (Rodrigues & Nunes, 2002). bers of burrows and nests found in the Their breeding distributions in the Atlantic Vegetated Sea Cliffs of the Macaronesian Ocean are concentrated in Europe and Coasts habitat and in the Endemic most species have small world populations Macaronesian Heaths habitat are proba- (Monteiro et al., 1999) being classified as bly related to human disturbance and globally threatened species (Collar et al., degradation of this last habitat with inva- 1994). The Azorean population of Cory’s sive alien species that are a threat to shearwater decreased around 50% between seabird populations (Groz & Pereira, 1996 and 2001 (Rodrigues & Nunes, 2002), 2005). Adults arrive in colonies by late- and a similar situation was observed for February, lay eggs from late-May to early- Common tern populations, estimated June and hatching is relatively synchro- around 4000 breeding couples for 1992 (del nous, most chicks hatching between 18 Nevo et al. 1993), against 2000 breeding and 31 July (Granadeiro, 1991). Young couples for year 2000 (Rodrigues & Nunes, birds fledge from late-October to early- 2002), probably due to the impact of con- November (Monteiro et al., 1996b). They tinuous lost of their habitats. lay only one egg per year and do not People’s access to nests and burrows replace it if it is damaged or lost soon represents an important threat over after laying, so there is an ecological sig- seabirds in the islet, and several impacts nificance when a couple looses their egg, from recreation and vandalism, are leading all the dispended energy is lost and it is to their distraction from normal activities; one less breading couple. parents spend less time tending young Common terns breed in inaccessible birds or eggs, flying away from nests, leav- rocks with Vegetated Sea Cliffs of the ing eggs or chicks vulnerable to predators Macaronesian Coasts habitat, where and amenity, nests are destroyed and RODRIGUES ET AL: SEABIRD CONSERVATION AT ILHÉU DE VILA FRANCA 223 seabirds entirely abandon the colonies. graphic changes in a population over time These impacts can affect Azorean seabirds, (i.e., assessing population size, adult sur- particularly Common terns, since the vival, and juvenile recruitment) (Brichetti et colony of IVFC represents one of the al., 2000) and could be used to evaluate the largest in the Azores. effect of the habitat restoration pro- Due to the importance of the Azores gramme. archipelago for seabirds in Europe, it is Moreover, seabirds are believed to con- fundamental to protect every natural habi- stitute useful samplers of the marine envi- tat and to conserve the few areas where ronmental since they have been recognized they breed, usually steep scarps and islets as potentially useful and economical indi- (Monteiro et al, 1996b, 1999; Ramos et al., cators of the status of marine environment 1997). and, in particular, the status of commercial- In conclusion, results from the present ly important prey stocks (Furness & work indicate that IVFC plays an impor- Greenwood, 1993). tant role on the conservation of Cory’s shearwater and Common tern populations, ACKNOWLEDGEMENTS since hundreds of couples of these two species breed on the islet. But this impor- We are grateful to Professor António M. tance can be threatened by the continuous de Frias Martins for the opportunity to degradation of their habitats. undertake this research. Seabirds become mature at a late age, This project was supported by the experience low annual fecundity, often Third International Workshop of refrain from breeding, and enjoy annual Malacology and Marine Biology, Vila adult survival rates as high as 98%. This Franca do Campo, São Miguel, Azores, July suite of life history characteristics limits the 2006. capacity for seabird populations to recover The experiments performed for the pre- quickly from major perturbations, and pre- sent study comply with the laws of the sents important conservation challenges country in which they were performed. (Russell, 1999). An urgent management plan for IVFC LITERATURE CITED is necessary, in order to conserve the natur- al habitats of the islet and protect their BACKELJAU, T., K. BREUGELMANS, C. seabird populations. BRITO, L. DE BRUYN, H. DE WOLF & According to Groz & Pereira (2005), J. TIMMERMANS, 1995. Macro- islets habitats are expected to respond geographic genetic homogeneity in rapidly to habitat restoration, so it is urgent Littorina striata from the Azores to implement an habitat restoration pro- (Mollusca: Prosobranchia). In: MART- gram and a major efficient islet control to INS, A..F. (ed.), The Marine Fauna and people access, in order to improve seabirds Flora of the Azores (Proceedings of the breeding conditions on the islet. A well- Second International Workshop of designed legal and institutional framework Malacology and Marine Biology, Vila is essential to provide a basis for effective Franca do Campo, São Miguel, Azores, eradication and control measures of alien 1991). Açoreana, Supplement [4]:159- species (Shine et al., 2000), control of 171. soil erosion and multiplication and re- BOLTON, M., 2001. 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