Census of birdlife in Vigur Island, Westfjords, Iceland. Translated title: Skráning fuglalífs á Vigur í vestfjörðum, Íslandi. Translated title: Recensement de l'avifaune de l'île de Vigur, Westfjords, Islande.

Known for its exceptional biodiversity, Vigur Island (Westfjords, Iceland) welcomes several bird colonies each year. This 2 km long, 400 m wide island also hosts an eiderdown farm and touristic visits from late June to September. Hence, the aim of the 2021 summer research campaign was to estimate the population of different bird species, and to establish their abundance in order to create a valuable database that could be used for further research and monitoring. The bird census was conducted both on land and sea, as far as permitted, with the use of binoculars. We focused on the main bird species found on the island: black guillemots, Northern fulmars, great cormorants, both Herring and Lesser black-backed gulls, Eurasian oystercatchers, and Arctic terns. Atlantic puffins were very common on the island, but no count was made for this species. The Arctic tern population was estimated by dividing the land into square units and subsequently counting nests using the line-over-line method. More precisely, the Arctic tern colony population was estimated using a transect line method (20 x 30m units). Due to the hatching of the eggs, the survey had to be stopped and only covered 60% of the colony area. Other species were counted by two observers following the coast of the island 5 times, with a maximum of two days apart. Gulls were counted together to avoid likely misidentifications. Potential differences among observers were addressed through a Wilcoxon-Mann-Whitney test for all bird species. The results show that in summer 2021, Vigur potentially hosted 1092±246 black guillemots, 28±8 oystercatchers, 19±8 cormorants, 120±34 fulmars, and 58±20 gulls. We counted 440 occupied Arctic tern nests, leading to an estimation of 880 breeding adults. The guillemot population has increased up to threefold over previous or local estimates (Náttrufristofnun Islands, 2021b). Comparison for the other species was impossible, as no counts were previously conducted. This report also details difficulties and specificities linked to the island and its unique configuration. Consequently, this report constitutes a baseline to monitor bird populations in Vigur. Then, we recommend regularly updating the data, to adopt appropriate conservation and tourism strategies.

Vigur, þekkt fyrir einstakan líffræðilegan fjölbreytileika, býður velkomnar ýmsar fuglahjarðir á ári hverju. Þessi 2km langa eyja, aðeins 400m að breidd, ber einnig að geyma friðlýst æðarvarp og er sótt af ferðamönnum allt frá lok júní til septembers. Markmið rannsóknar sumarsins 2021 var að stofna viðmið og telja fjölda ýmsa fuglategunda til að fá dýrmætt gagnasafn sem nota mætti til frekari rannsókna og eftirlits. Tal fuglanna var framkvæmt bæði á landi og sjó, svo framarlega sem aðstæður leyfðu, með notkun sjónauka. Við einblíndum á helstu fuglategundum eyjarinnar, en talinn var fjöldi teista, fýla, dílaskarfa, silfur- og sílamáva, tjalda, lunda og kría. Lundar voru verulega algengir á eyjunni, en engin talning var gerð á þessari tegund. Fjöldi kría var áætlað með sniðatalningu, en talningarsvæðið var skipt niður í ferkantaðar einingar og hreiður talin í hverri einingu með „line-over-line” aðferð. Nánar tiltekið var fjöldi kría áætlaður út frá sniðtalningu (20 x 30m snið). Að sökum útklekjun eggja varð rannsóknin stöðvuð, en hún náði aðeins yfir um 60% heildar fuglahjarðar svæðisins. Á öðrum tegundum var framkvæmd full talning fuglanna af tveimur rannsakendum, fimm sinnum, fylgjandi strönd eyjunnar, með að því mest tveggja daga millibili. Silfur- og sílamávar voru taldir saman til að koma í veg fyrir væntanlegs miskennsl. Tekist var á við mögulegum mismunum í talningum rannsakenda með Wilcoxon-Mann-Whitney prófi. Niðurstöður talningunnar sumars 2021 sýna að á Vigri var að finna 1092±246 teistur, 28±8 tjalda, 198 skarfa, 120±34 fýla og 58±20 máva. Við töldum 440 hreiður, sem gefa í skyn áætlaðar 880 fullorðnar kríur að varpi. Stofn teista hefur þrefaldast frá síðustu áætluðu tölum (Náttrufræðistofnun Islands, 2021b). Samanburður var ótækur fyrir hinar tegundirnar, þar sem engin fyrri talning hafði verið gerð. Skýrsla þessi lýsir einnig smáatriði og tormerki tengd eyjunni og eigind hennar. Á þann veg þjónar þessi skýrsla tilgangi viðmiðs fyrir frekari eftirliti fuglafjölda í Vigri. Við hvetjum til frekari rannsókna og reglulegrar uppfærslna til að rækta sæmandi náttúruvernd og ferðamála aðferðafræði.

Connue pour sa biodiversité exceptionnelle, l’île de Vigur (Westfjords, Islande) accueille chaque année plusieurs colonies d’oiseaux. Longue de 2 km, pour 400 m de largeur, l’île abrite également une ferme travaillant le duvet de canard Eider, ainsi que des visites touristiques de fin juin à septembre. Ainsi, l’objectif de la campagne de recherche de l’été 2021 était d’estimer les populations de différentes espèces d’oiseaux, et de caractériser leur abondance. Cela, dans le but de développer une base de données qui puissent être utilisée pour des projets de recherche futurs. Les oiseaux ont été comptés sur terre et en mer, aussi loin que le permet l’usage de jumelles. Nous nous sommes focalisés sur les principales espèces présentes sur l’île : le Guillemot à miroir, le Fulmar boréal, le Grand Cormoran, les Goélands bruns et argentés, l’Huîtrier pie et la Sterne Arctique. La population de Sternes Arctiques a été estimé en divisant l’aire de la colonie en unités rectangulaires, afin de simplifier le comptage des nids, selon la méthode des transects. Plus précisément, la population au moyen d’unité de dimensions 20 x 30 m. En raison de l’éclosion des œufs, le comptage a dû être interrompu et seulement 60% de l’aire de la colonie ont été couverts. Les autres espèces ont été comptées à cinq reprises par deux observateurs marchant le long de la côte, avec un maximum de deux jours d'intervalle. Les goélands ont été comptés ensemble afin d’éviter de possibles erreurs d'identification. Les différences potentielles entre les observateurs ont été évalués au moyen d'un test de Wilcoxon-Mann-Whitney pour toutes les espèces d'oiseaux. Les résultats montrent qu'à l'été 2021, Vigur a potentiellement hébergé 1092±246 guillemots à miroir, 28±8 huîtriers pie, 19±8 cormorans, 120±34 fulmars et 58±20 goélands. Nous avons compté 440 nids occupés de sternes arctiques, conduisant à une estimation de 880 adultes reproducteurs. La population de guillemots a triplé par rapport aux estimations locales précédentes (Náttrufristofnun Islands, 2021b). La comparaison pour les autres espèces s’avère impossible, puisqu’aucun comptage n'a été effectué auparavant. Ce rapport détaille également les difficultés et spécificités liées à l'île et à sa configuration unique. Par conséquent, ce rapport constitue une référence pour le suivi des populations d'oiseaux à Vigur. Un travail que nous invitons à poursuivre, afin d'adopter des stratégies de conservation et de tourisme durables et appropriées.