# Comparing fieldwork, local knowledge and citizen science for bird monitoring in Súðavík, Iceland

David Pierre Milesi-Gaches

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## To cite this version:

David Pierre Milesi-Gaches. Comparing fieldwork, local knowledge and citizen science for bird monitoring in Súðavík, Iceland. Carnets Natures, 2026, 13, pp.1-14. hal-05475925

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Submitted on 25 Jan 2026

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# Comparing fieldwork, local knowledge and citizen science for bird monitoring in Súðavík, Iceland

David Pierre Milesi-Gaches<fnref n="1" />

## Abstract

This study investigates the complementary roles of structured fieldwork, local contributors, and online citizen science platforms in building a bird species inventory in Súðavík, Westfjords, Iceland. A total of 70 bird species were recorded, including 23 confirmed breeders on the Langeyri peninsula. Local contributors added rare and seasonal records to field observations, often compensating for gaps caused by harsh weather or limited access. Online data helped validate observations and extended spatial coverage. The integration of these approaches improved species detection, reduced uncertainty, and highlighted the value of citizen science, especially in remote regions facing logistical constraints. Despite some limitations, such as observer biases or identification challenges, citizen science proved to be a critical tool for enhancing biodiversity monitoring.

**Keywords:** Environment, ornithology, birds, Iceland, citizen science.

## Comparaison entre observations de terrain, connaissances locales et science participative dans le suivi des oiseaux à Súðavík, Islande

## Résumé

Cette étude examine les rôles complémentaires du travail de terrain, des contributions d'observateurs locaux et des plateformes de science participative en ligne dans l'élaboration d'un inventaire des espèces d'oiseaux à Súðavík, dans les fjords de l'ouest islandais. Au total, 70 espèces d'oiseaux ont été recensées, dont 23 confirmées comme nicheuses sur la péninsule de Langeyri. Les contributeurs locaux ont apporté des données rares ou saisonnières, venant compléter les observations de terrain, notamment lorsque les conditions météorologiques ou l'accès au site limitent le travail de terrain. Les données en ligne ont aidé à valider certaines observations et à élargir la couverture spatiale. L'intégration de ces approches a amélioré la détection des espèces, réduit l'incertitude et mis en lumière la valeur de la science participative, en particulier dans les régions reculées soumises à des contraintes logistiques. Malgré certaines limites, comme les biais d'observation ou les difficultés d'identification, la science participative s'est révélée être un outil essentiel pour renforcer le suivi de la biodiversité.

**Mots clés :** Environnement, ornithologie, oiseaux, Islande, science participative.

## 1. Introduction

Iceland holds a unique position in the field of ornithology due to its rich birdlife and geographical location at the intersection of migratory routes between North America and Europe. The island's diverse habitats, including vast wetlands, coastal cliffs, and volcanic landscapes, provide breeding grounds for numerous seabirds and waterfowl species, some of which have globally significant populations (Petersen, 1998; Asbirk, 1997).

In recent years, Iceland has experienced exponential growth in tourism (Maher et al., 2022), which brings

increased human presence to wild and remote areas. Regions offering wildlife observation, such as birdwatching, face significant anthropogenic impacts (Croxall et al., 2012), which interact with broader global challenges like climate change (Daunt & Mitchell, 2013; Paleczny et al., 2015). The consequences of these combined pressures include habitat degradation and disruptions in species' breeding cycles, such as reduced incubation periods (Croxall et al., 2012; Dias et al., 2019).

Before implementing effective management actions, it is crucial to develop a comprehensive understanding of the ecological, environmental, and social dynamics

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<footnote n="1">1. University of South Bohemia, Czech Republic, Department of Zoology, 420 Súðavík, Iceland: milesi.david@gmail.com</footnote>
that shape these ecosystems. Interventions based on
incomplete knowledge risk unintended consequences,
while a deeper understanding supports adaptive
management and long-term sustainability (Westgate
et al., 2013). As Holling and Meffe (1996) emphasised,
successful ecosystem management requires a
precautionary approach that accounts for the complexities
and uncertainties inherent in natural systems.

Citizen science is increasingly recognised for its
potential to engage extensive networks of volunteers,
thereby enabling data collection on a scale and resolution
often unattainable by individual researchers. As well, it
allows the execution of conservation initiatives which
wouldn't be feasible through traditional research
methods alone (Kobori et al., 2016; Miller-Rushing
et al. 2012; Silvertown 2009). It not only supplements
traditional research methods but also leverages local
knowledge, especially vital in complex environments
like urban ecology where private lands remain largely
inaccessible for structured scientific study (Evans et al.
2005; Lepczyk, 2005; Kobori & Primack 2003). One
successful example of citizen science in action is the
eBird project, which collects approximately five million
bird observations each month and has contributed
to around 100 peer-reviewed articles across various
scientific disciplines (Sullivan et al. 2014).

However, utilising citizen science data is not without
challenges, notably concerning data accuracy. Issues
can arise from the predominance of records for common
species over rare ones, as well as the spatial precision
and documentation quality of the collected data (Young
et al., 2019). These limitations can be mitigated by
providing volunteers with adequate training and the
necessary tools for accurate data collection. Concerns
about species misidentification, often cited due to the
involvement of non-professionals, have been addressed
in several studies which show that well-designed citizen
science projects can achieve high levels of accuracy
(Gorleri et al., 2023; Greenwood, 2007; Cohn, 2008).

In addition to its contribution to scientific research,
citizen science holds educational value, helping to
demystify the scientific process and foster lifelong
learning among participants of all ages (Bonney et al.
2009; Brewer, 2002). Therefore, while challenges exist,
the potential benefits of integrating citizen science into
contemporary research are manifold, particularly in
improving knowledge of undersampled taxa and regions
in the Arctic (Fraisl et al., 2022).

This study examines how different sources of
information can be combined to create a bird species
inventory in Súðavík, Iceland, and to evaluate their
respective contributions to local monitoring. Súðavík,
with its mix of privately owned lands and areas near
touristic and industrial activities, presents an opportunity
to examine the potential impacts of human disturbances
on bird populations. Given the Icelandic Tourist Board's
(Ferðamálastofa) policy framework for sustainable
tourism through 2030, which emphasises research-based

decision-making (Ferðamálastofa, 2020), establishing a
thorough understanding of local birdlife is important for
guiding future conservation efforts and informing local
governance (Moore et al., 2020).

To this end, I combine three complementary data
sources: (1) online records from citizen science platforms,
(2) field observations collected in Álftafjörður between
2021 and 2023, and (3) observations from experienced
local birdwatchers. Species are classified according
to their pattern of occurrence (e.g. breeding species,
regular visitors, occasional visitors, rare sightings), and
their conservation status is reported. By assessing the
strengths and limitations of each data source, this study
discusses their complementarity for monitoring bird
communities at the local scale.

A selection of emblematic bird species from the
Súðavík area is presented in **Fig. 1**, providing a visual
overview of the local avifauna.

## 2. Methods

### 2.1. Study area

Súðavík, nested within Álftafjörður fjord in Iceland's Westfjords, is a pivotal fishing village located about 20 kilometres from Ísafjörður's urban centre. Súðavík holds both ecological and touristic significance. The Arctic Fox Centre (Melrakkasetur Íslands, 2023), and sea angling ventures by Iceland Sea Angling (2023) bring tourists that are sensitive to wildlife. Notable natural landmarks encompass the Langeyri peninsula. Despite its commercial and industrial undertakings, it stands out as an important breeding and nesting hub for various bird species (Fig. 2).

Recent initiatives have highlighted the Langeyri
peninsula as a key area for development within Súðavík.
Human activities occupy a space of 39,600 square
metres, constituting 26% of the peninsula's total area of
150,000 square metres. The majority of the peninsula
remains in its pristine state, apart from the presence of a
minor pathway (Fig. 2).

The ecological composition of Langeyri is diverse,
featuring rocky coastlines, barren coastal fields, a small
cultivated area, shrublands, and a freshwater pond
(Fig. 2). On an annual basis, this habitat serves as an
attraction for various migratory bird species including
Arctic terns *Sterna paradisaea* (Pontoppidan, 1763),
Black-headed gulls *Chroicocephalus ridibundus*
(Linnaeus, 1766), Common eiders *Somateria mollissima*
(Linnaeus, 1758), Common redshanks *Tringa totanus*
(Linnaeus, 1758) or Eurasian oystercatchers *Haematopus
ostralegus* (Linnaeus, 1758).

Although the Langeyri peninsula serves as the
primary avian habitat in Súðavík, a variety of other bird
species can also be observed in different areas within the
town and further in the Álftafjörður fjord. For example,
Common redpoll (*Acanthis flammea*, Linnaeus, 1758)
can be spotted within the town itself.
<figure><img src="image_4.png" /><figcaption>**Fig. 1** - Examples of typical bird species in the Súðavík area, Westfjords, Iceland. (A) Arctic tern *Sterna paradisaea*. (B) Common eider *Somateria mollissima* (female). (C) Atlantic puffin *Fratercula arctica*. (D) Black-headed gull *Chroicocephalus ridibundus*. (E) Black guillemot *Cephalus grylle*. (F) Black-tailed godwit *Limosa limosa*. (G) European golden plover *Pluvialis apricaria*. (H) Red-throated diver *Gavia stellata*. (I) Harlequin duck *Histrionicus histrionicus* (male). (Photographs: Pixabay, Saxifraga)</figcaption></figure>

Near the harbour, species such as the Black guillemot and the Northern fulmar (*Fulmarus glacialis*, Linnaeus, 1761) are frequently sighted. Further into the fjord, the Whooper swan (*Cygnus cygnus*, Linnaeus, 1758) can be seen alongside the seashore and in fields.

While Súðavík urban area remains limited, numerous small trees are present on the mountainside, in the backyard of houses, thus increasing the likelihood that owners can observe bird species appreciating these habitats.

## 2.2. Data collection

### 2.2.1. Online records from citizen science platforms

Data from citizen science platforms were scrutinised and incorporated when relevant. Records from eBird (eBird, 2023) were evaluated with particular attention to observer reliability (e.g. biological background, ornithological expertise or status as experienced birdwatcher), and only sightings with sufficient evidence such as photographs or multiple independent reports were

<figure><img src="image_5.png" /><figcaption>**Fig. 2** - Map of Súðavík showing key districts and areas. (1) Industrial facilities. (2) The Arctic Fox Centre. (3) Iceland Sea Angling (Basemap: Loftmyndir ehf).</figcaption></figure>
retained. Additional species records were obtained from the Global Biodiversity Information Facility (GBIF.org, 2023), using a search polygon covering approximately $2.21 \times 10^9$ m² around Súðavík to spatially filter queries.

### 2.2.2. Field observations

Bird species were recorded during fieldwork carried out in Álftafjörður between 2021 and 2023. These observations included direct sightings made while conducting research on seal behaviour, general wildlife surveys, a plant inventory in Langeyri (Milesi-Gaches, 2025), and experiments on nest-defence behaviour in *Sterna paradisaea* (Tabl. 1). Additional opportunistic sightings were also noted in the area during routine daily activities.

### 2.2.3. Observations from experienced local contributors

Additionally, local expertise was gathered through consultations with two experienced birdwatchers from

the community, whom I connected with via word of mouth. Their long-term observations provided valuable insights into species behaviour and distribution, complementing the fieldwork data. These consultations also allowed for an assessment of their skill levels and the reliability of their observations (Cohn, 2008).

### 2.2.4. Data categorisation and analysis

Species were assigned to taxonomic families and classified according to their pattern of occurrence in Súðavík, following the criteria presented in Tabl. 2. The national conservation status of each species was compiled using the 2018 red list published by the Icelandic Institute of Natural History (Náttúrufræðistofnun Íslands, 2018).

## 3. Results

A total of 70 avian species were identified (Tabl. 3), of which 23 breed and nest on the Langeyri peninsula (Fig. 3). Among these, 17 are regular visitors, indicating

<table><caption>Tabl. 1 - Summary of secondary fieldwork activities detailing observational and experimental studies conducted on Arctic fauna and flora, 2023–2024.</caption><thead><tr><td>Secondary fieldwork</td><td>Period</td><td>Total duration</td><td>Description</td></tr></thead><tbody><tr><td>Behavioural ecology or harbour and grey seals</td><td>2023-2024</td><td>70 hours</td><td>Direct observations of seals' behaviour and interspecies interactions to assess behavioural patterns.</td></tr><tr><td>Habitat and behaviour of pre-nesting Arctic terns</td><td>5-10<br>June 2023</td><td>2 hours</td><td>20-minute observation sessions and experimentation (flight initiation distance).</td></tr><tr><td>Nest defence behaviour of Arctic terns</td><td>24-26<br>June 2023</td><td>24 hours</td><td>20-minute experiments involving dummy presentations to observe defence behaviours, with 40-minute intervals between sessions.</td></tr><tr><td>Flora species identification (Langeyri peninsula)</td><td>12-19<br>August 2023</td><td>30 hours</td><td>Identification and documentation of flora species within the Langeyri peninsula.</td></tr><tr><td>Nesting preferences of black guillemots</td><td>Summer<br>2023</td><td>10 hours</td><td>Regular observations of black guillemots in the harbour area to locate and document nesting preferences.</td></tr></tbody></table>

<table><caption>Tabl. 2 - Classification of avian visitors to the Langeyri peninsula, Súðavík, and the Álftafjörður fjord based on frequency and patterns of occurrence.</caption><thead><tr><td>Category</td><td>Definition</td></tr></thead><tbody><tr><td>Breeding and nesting birds</td><td>All species breeding and/or nesting in Langeyri.</td></tr><tr><td>Regular visitors</td><td>Refers to species that are consistently observed in the Langeyri peninsula, Súðavík, and the Álftafjörður fjord, engaging in routine activities like feeding and preying. These species are typically sighted either daily or multiple times per week.</td></tr><tr><td>Occasional visitors</td><td>Refers to species that are sporadically observed in the Langeyri peninsula, Súðavík, and the Álftafjörður fjord. These species are sighted with varying frequency, ranging from a few times a week to multiple times per month.</td></tr><tr><td>Rare visitors</td><td>Refers to species that are infrequently observed in the Langeyri peninsula, Súðavík, and the Álftafjörður fjord, with sightings occurring once a month or less. This category also includes species that were observed only during a single year or breeding season, as well as species that were formerly regular or occasional visitors but have not been observed for several years.</td></tr><tr><td>Migratory stopover visitors</td><td>Refers to species known to make brief sojourns in the Langeyri peninsula, Súðavík, and the Álftafjörður fjord as part of their migratory routes.</td></tr></tbody></table>
Birds in Súðavík

<figure><img src="image_6.png" /><figcaption>Fig. 3 - Summary of bird species identified around Súðavík.</figcaption></figure>

that 40 species inhabit Súðavík, utilising the peninsula, the urban area, and nearby environs to meet their daily requirements. The waterbird family is the predominant one among the eight families identified. Notably, waders had a strong representation among both breeding and nesting species, with seven species classified in this category.

The families of gulls and their relatives, passerines, seabirds, waders, and waterbirds are represented across breeding and nesting birds, as well as regular, occasional, and rare visitors. Only three families are exclusive to a single category: a singular owl species manifests as a regular visitor, while one species of grouse and three raptor species are classified as rare visitors. Migratory stopover visitors were only observed from the waterbird family (Tabl. 3).

Due to its diverse habitats, the Langeyri peninsula stands out as the primary nesting site in Súðavík. The distribution of nesting bird species aligns with anticipated patterns in Iceland. Particularly noteworthy is the presence of Black guillemots *Cephus grylle* (Linnaeus, 1758). While most alcids are colonial, Black guillemots can exhibit more dispersed nesting habits (Preston, 1968). This is evident in Súðavík, where a few pairs have been observed nesting along the seashore and within the harbour.

### 3.1. Conservation status

Among the 70 identified species, one (the little auk *Alle alle* Linnaeus, 1758) is regionally extinct in Iceland, two are critically endangered (the Atlantic puffin and
<table><caption>Tabl. 3 - Bird species observed in the Súðavík area, categorised by status.</caption><thead><tr><th>Type</th><th>Family</th><th>Specie</th><th>Scientific name</th></tr></thead><tbody><tr><td rowspan="14">Breeding and nesting birds</td><td rowspan="3">Gulls and relative</td><td>Arctic tern</td><td>Sterna paradisaea</td></tr><tr><td>Black-headed gull</td><td>Chroicocephalus ridibundus</td></tr><tr><td>Lesser black-backed gull</td><td>Larus fuscus</td></tr><tr><td rowspan="5">Passerines</td><td>Eurasian wren</td><td>Troglodytes troglodytes</td></tr><tr><td>Meadow pipit</td><td>Anthus pratensis</td></tr><tr><td>Northern wheatear</td><td>Oenanthe oenanthe</td></tr><tr><td>Redwing</td><td>Turdus iliacus</td></tr><tr><td>White wagtail</td><td>Motacilla alba</td></tr><tr><td>Seabirds</td><td>Black guillemot</td><td>Cephus grylle</td></tr><tr><td rowspan="7">Waders</td><td>Black-tailed godwit</td><td>Limosa limosa</td></tr><tr><td>Common redshank</td><td>Tringa totanus</td></tr><tr><td>Common ringed plover</td><td>Charadrius hiaticul</td></tr><tr><td>Common snipe</td><td>Gallinago gallinago</td></tr><tr><td>Eurasian oystercatcher</td><td>Haematopus ostralegus</td></tr><tr><td>European golden plover</td><td>Pluvialis apricaria</td></tr><tr><td>Red-necked phalarope</td><td>Phalaropus lobatus</td></tr><tr><td rowspan="7">Waterbirds</td><td>Common eider</td><td>Somateria mollissima</td></tr><tr><td>Eurasian wigeon</td><td>Mareca penelope</td></tr><tr><td>Greylag goose</td><td>Anser anser</td></tr><tr><td>Mallard</td><td>Anas platyrhynchos</td></tr><tr><td>Red-breasted merganser</td><td>Mergus serrator</td></tr><tr><td>Red-throated diver</td><td>Gavia stellata</td></tr><tr><td>Tufted duck</td><td>Aythya fuligula</td></tr><tr><td rowspan="20">Regular visitors</td><td rowspan="6">Gulls and relative</td><td>Arctic skua</td><td>Stercorarius parasiticus</td></tr><tr><td>Black-legged Kittiwake</td><td>Rissa tridactyla</td></tr><tr><td>Common gull</td><td>Larus canus</td></tr><tr><td>Glaucous gull</td><td>Larus hyperboreus</td></tr><tr><td>Great black-backed gull</td><td>Larus marinus</td></tr><tr><td>Herring gull</td><td>Larus argentatus</td></tr><tr><td>Owls</td><td>Short-eared owl</td><td>Asio flammeus</td></tr><tr><td rowspan="2">Passerines</td><td>Common raven</td><td>Corvus corax</td></tr><tr><td>Common redpoll</td><td>Acanthis flammea</td></tr><tr><td rowspan="5">Seabirds</td><td>Snow bunting</td><td>Plectrophenax nivalis</td></tr><tr><td>Atlantic puffin</td><td>Fratercula arctica</td></tr><tr><td>Great cormorant</td><td>Phalacrocorax carbo</td></tr><tr><td>Northern fulmar</td><td>Fulmarus glacialis</td></tr><tr><td>Whimbrel</td><td>Numenius phaeopus</td></tr><tr><td rowspan="3">Waders</td><td>Eurasian teal</td><td>Anas crecca</td></tr><tr><td>Long-tailed duck</td><td>Clangula hyemalis</td></tr><tr><td>Whooper swan</td><td>Cygnus cygnus</td></tr><tr><td rowspan="4">Waterbirds</td><td>Gulls and relative</td><td>Iceland Gull</td><td>Larus glaucooides</td></tr><tr><td rowspan="2">Passerines</td><td>Barn Swallow</td><td>Hirundo rustica</td></tr><tr><td>Common starling</td><td>Sturnus vulgaris</td></tr></tbody></table>
<table><tbody><tr><td></td><td>Seabirds</td><td>European Shag</td><td>Gulosus aristotelis</td></tr><tr><td></td><td>Waders</td><td>Purple Sandpiper</td><td>Calidris maritima</td></tr><tr><td></td><td></td><td>Red knot</td><td>Calidris canutus</td></tr><tr><td></td><td></td><td>Ruddy turnstone</td><td>Arenaria interpres</td></tr><tr><td></td><td></td><td>Sanderling</td><td>Calidris alba</td></tr><tr><td></td><td>Waterbirds</td><td>Common shelduck</td><td>Tadorna tadorna</td></tr><tr><td></td><td></td><td>Greater Scaup</td><td>Aythya marila</td></tr><tr><td></td><td></td><td>Northern Pintail</td><td>Anas acuta</td></tr><tr><td rowspan="10">Rare visitors</td><td>Grouses</td><td>Rock Ptarmigan</td><td>Lagopus muta</td></tr><tr><td>Gulls and relative</td><td>Great skua</td><td>Stercorarius skua</td></tr><tr><td>Passerines</td><td>Bohemian waxwing</td><td>Bombycilla garrulus</td></tr><tr><td></td><td>Common blackbird</td><td>Turdus merula</td></tr><tr><td>Raptors</td><td>Gyrfalcon</td><td>Falco rusticolus</td></tr><tr><td></td><td>Merlin</td><td>Falco columbarius</td></tr><tr><td></td><td>White-tailed eagle</td><td>Haliaeetus albicilla</td></tr><tr><td>Seabirds</td><td>Common Murre</td><td>Uria aalge</td></tr><tr><td></td><td>Little auk</td><td>Alle alle</td></tr><tr><td></td><td>Razorbill</td><td>Alca torda</td></tr><tr><td>Waders</td><td>Eurasian curlew</td><td>Numenius arquata</td></tr><tr><td></td><td>Grey heron</td><td>Ardea cinerea</td></tr><tr><td>Waterbirds</td><td>Goosander</td><td>Mergus merganser</td></tr><tr><td></td><td>Harlequin duck</td><td>Histrionicus histrionicus</td></tr><tr><td></td><td>King eider</td><td>Somateria spectabilis</td></tr><tr><td></td><td>Mandarin duck</td><td>Aix galericulata</td></tr><tr><td rowspan="3">Migratory stopover visitors</td><td>Waterbirds</td><td>Barnacle goose</td><td>Branta leucopsis</td></tr><tr><td></td><td>Brent goose</td><td>Branta bernicla</td></tr><tr><td></td><td>Great northern diver</td><td>Gavia immer</td></tr></tbody></table>

great skua *Stercorarius skua*, Brünnich, 1764), and nine are classified as endangered (Fig. 6). The black guillemot, which nests and breeds in Súðavík, is among the endangered species. Of these nine endangered species, two (greater scaup *Aythya marila*, Linnaeus, 1761; and purple sandpiper *Calidris maritima*, Brünnich, 1764) are occasional visitors, while the others are regular visitors. Eleven species are vulnerable, including three breeding and nesting species: the Arctic tern, Eurasian oystercatcher, and common eider.

## 3.2. Contribution of the three data sources

The bird species list was compiled from three complementary sources: online records from citizen science platforms (eBird, GBIF), my own field observations, input from two local birdwatchers with over 30 years of experience each. While both local birdwatchers are highly knowledgeable, only one is proficient in bird photography. Both possess a deep understanding of bird ecology, especially within Iceland. The eBird and GBIF databases helped document several species that were not recorded during fieldwork or

by local observers, particularly among seabirds and waterbirds. Conversely, species frequenting private gardens or residential trees were more likely to be documented by local birdwatchers. Neither the local birdwatchers nor I had submitted observations directly to online databases (Tabl. 4).

When breaking down species identification by family, local contributor 1 observed the most diversity, identifying 69 out of the 70 species on the list. The lone missing species from contributor 1's list, the Bohemian waxwing *Bombycilla garrulus* (Linnaeus, 1758), was only observed by local contributor 2. Known as a vagrant species in Iceland, the Bohemian waxwing was photographed by contributor 2 while feeding in a private garden, reducing its detectability outside private property.

All sources identified species belonging to gulls and relatives, seabirds, passerines, waterbirds, and waders. Raptors, grouse, and owls were less frequently observed in Súðavík. For instance, I did not encounter any raptors during fieldwork, and the Short-eared owl *Asio flammeus* (Pontoppidan, 1763) was exclusively noted by local contributor 1.
<figure><img src="image_7.png" /><figcaption>**Fig. 4** - Number of species identified by family and by data source.</figcaption></figure>

Breeding and nesting birds were the most frequently identified across sources, followed by regular visitors. Both local contributors and online records documented more rare visitors than occasional ones (Fig. 5).

**4. Discussion**

This paper aimed to evaluate the contribution of online records from citizen science platforms (eBird, GBIF), field observations, and input from local contributors to the development of a bird species inventory in

comparison to traditional fieldwork. Although the fieldwork spanned three years, contributions from local residents identified a greater number of bird species and provided information extending beyond the 2021–2023 fieldwork period. Despite Iceland being a renowned destination for birdwatchers, global databases like eBird and GBIF did not offer more comprehensive data than what was gathered by local contributors. However, these databases played a crucial role in validating the accuracy of both the fieldwork and local citizen reports through cross-referencing species identifications. Registered

<figure><img src="image_8.png" /><figcaption>**Fig. 5** - Number of species identified by pattern of occurrence and by data source.</figcaption></figure>
<table><caption>**Tabl. 4** - Number of bird species identified by sources for Súðavík.</caption><thead><tr><th>Source</th><th>Own fieldwork</th><th>Local contributor 1</th><th>Local contributor 2</th><th>eBird</th><th>GBIF</th></tr></thead><tbody><tr><td>Number of species</td><td>51</td><td>69</td><td>42</td><td>46</td><td>56</td></tr></tbody></table>

## Icelandic conservation status
of avian species observed in Súðavík, Westfjords

<figure><img src="image_9.png" /></figure>

**Common redshank** Bird species breeding and nesting in the Langeyri peninsula.

* Categories as defined by the International Union for Conservation of Nature (IUCN), with the classification from Náttúrufræðistofnun Íslands (Icelandic Institute of Natural History, IINH).

<caption>**Fig. 6** - Bird species identified in Súðavík and their conservation status in Iceland (amended from Náttúrufræðistofnun Íslands).</caption>

observations were often accompanied by detailed notes on species characteristics, such as breeding status, age (juvenile or adult), and photographs, enhancing the reliability of the data.

While conducting fieldwork around nesting areas is relatively straightforward for an experienced ornithologist during the breeding season, it remains time-consuming to explore and monitor more distant areas and different times of the year. The most challenging task was recording birds during migratory stopovers due to their fleeting presence. Identifying 51 species in this study was only possible because of my involvement in other research projects in the area, allowing for extensive time spent outdoors throughout the spring, summer, and autumn. Living locally also provided an observational advantage, introducing a positive bias compared to researchers based outside the region. For

example, although I did not record any raptors during formal fieldwork, I observed a white-tailed eagle twice during the winter of 2023-2024 while commuting between Ísafjörður and Súðavík, approximately 6 km from the study area (66.092329, -23.016051). This proximity helped to validate similar sightings reported by local contributors, supporting the reliability of these observations. This complementarity also reflects my own dual position as both a researcher conducting formal fieldwork and a local observer living year-round in the area, which allowed me to contribute in both structured and informal ways.

The contribution of citizens to the bird species inventory in Súðavík did not surpass or replace conventional methods. Instead, it served as a complementary approach, providing valuable insights and helping to verify data from global databases and
<figure><img src="image_10.png" /><figcaption>**Fig. 7** - Each method's gaps and uncertainties are mitigated by the others, demonstrating their complementary roles in the bird species inventory process.</figcaption></figure>

fieldwork (Fig. 7). Each of the three approaches—online records, field observations, and local contributors—complemented the others, filling gaps and addressing uncertainties in the data from the other two methods. In addition to their complementarity, these approaches differ in the kind of contribution they typically offer (Tabl. 5). Fieldwork offered focused and repeatable. observations across key breeding habitats, while local contributors added long-term continuity and access to private areas. Online platforms, although more variable, contributed broader spatial coverage and useful records for cross-checking rare or occasional sightings.

When the aim of any study is to provide comprehensive information, including the presence of rare or vagrant bird species, all sources of data become essential, even if the sighting of a vagrant species does not fully reflect the typical bird ecology of a specific location. Just as researchers engage in continuous education and databases are regularly updated, it is equally important that citizens participating in research activities have opportunities to update their knowledge. Individuals interested in citizen science should have access to accurate information that helps them make comprehensive and reliable contributions to scientific efforts. However, a major challenge for the scientific community is to make the scientific process more accessible and to effectively communicate findings to a non-scientific audience (Brewer, 2002; Greenwood, 2007; Cohn, 2008).

Indeed, concerns frequently arise regarding the

accuracy of species identification in citizen science databases, primarily because data collection is often undertaken by non-professionals. Such misidentifications can lead to two concurrent types of errors: false positives, where a species is incorrectly reported, and false negatives, where the misidentified species goes unreported (Gorleri et al., 2023). Particularly in Iceland, certain bird species can be difficult to identify and distinguish from others with similar traits, such as juvenile seagulls, which often look alike across species. Similarly, female goosander *Mergus merganser* (Linnaeus, 1758) and red-breasted merganser *Mergus serrator* (Linnaeus, 1758) are hard to differentiate, with goosanders distinguishable primarily by their slightly curved beak or the subtle line separating their brown and white plumage (Fig. 8).

Additionally, lighting conditions at sunrise or sunset can further complicate bird identification, as colours and patterns become harder to discern. Mistakes in identification can stem not only from these environmental or morphological challenges but also from the observer's own overconfidence. Those who feel certain in their identification skills might overlook small but crucial details, leading to potential misidentifications.

In their comprehensive review of the eBird database focused on the southern Neotropics, particularly Argentina, Gorleri et al. (2023) analysed more than 104,000 images spanning 377 passerine species. Their findings revealed an impressive 97% accuracy rate in species identification across the dataset. However, it is
<table><caption>**Tabl. 5** - Summary of the specific contributions, strengths, and limitations of each data source used for the bird inventory in Súðavík, Iceland.</caption><thead><tr><td></td><td>Citizen science platforms</td><td>Field observations</td><td>Local contributors</td></tr></thead><tbody><tr><td>Origin</td><td>eBird, GBIF</td><td>Author's fieldwork (2021–2023)</td><td>Local birdwatchers</td></tr><tr><td>Mainly observed species</td><td>Waders, seabirds, wide range diversity</td><td>Common breeders, regular</td><td>Rare/vagrant, garden birds</td></tr><tr><td>Temporal coverage</td><td>Irregular, includes historical records</td><td>Spring to late summer</td><td>Year-round, multi-year</td></tr><tr><td>Spatial coverage</td><td>Wide geographic coverage, variable resolution</td><td>Specific transects and selected habitats</td><td>Residential and informal areas</td></tr><tr><td>Validation</td><td>Cross-referenced, sometimes vague</td><td>Direct validation by expert</td><td>Cross-checked via dialogue and repeated sightings</td></tr><tr><td>Strengths</td><td>Breadth of data, potential for independent verification</td><td>Precision, repeatability, breeding status</td><td>Contextual richness, insights into local trends</td></tr></tbody></table>

noteworthy that a small subset of species—about 10% (n=40)—that are typically difficult to identify had a considerably lower data quality, with precision or recall scores falling between 63% and 90%.

A key limitation of this study is the involvement of two skilled and experienced bird enthusiasts, in addition to my own residency in the area and the prominence of birdwatching tourism, which contributed to a more thorough inventory of bird species. This may have introduced biases, increasing the likelihood of focusing on birds from more accessible or nearby habitats, as well as on species that are particularly endangered or of specific research interest (Galván et al., 2022). Similarly, my side fieldwork on Arctic terns, black guillemots, and

seals increased my chances of observing shorebirds and seabirds, as these activities were concentrated near coastal habitats. Consequently, I was less likely to identify passerines, which typically inhabit areas farther from the coastline, such as the mountainside, where I spent less time. Compiling a comparable bird inventory in a different location could face greater challenges if local bird enthusiasts are absent or if global databases offer insufficient coverage.

The contribution of citizens in this study in Iceland was crucial, especially due to frequent adverse weather conditions that can limit the feasibility of fieldwork (e.g., road closures due to avalanche risks). In such circumstances, local contributors become an invaluable

<figure><img src="image_11.png" /><figcaption>**Fig. 8** - (A) A female goosander *Mergus merganser*. (B) A female red-breasted merganser *Mergus serrator*.</figcaption></figure>
<figure><img src="image_12.png" /><figcaption>**Fig. 9** - Examples of species recorded by a local contributor in Súðavík in winter. (A) *Bombycilla garrulus* (Bohemian waxwing). (B) *Asio flammeus* (short-eared owl). Both observations were documented within residential areas and contributed to confirming seasonal presence beyond formal fieldwork.</figcaption></figure>

<figure><img src="image_13.png" /></figure>

resource for ongoing bird monitoring, at least within their own properties, as demonstrated by the documented sighting of a vagrant Bohemian waxwing (Fig. 9).

This paper then corroborates that citizen science plays a valuable role in urban ecology, where private lands often represent significant but generally inaccessible ecological resources (Evans et al., 2005; Lepczyk, 2005; Kobori & Primack, 2003). This study further supports the findings of Kosmala et al. (2016), who emphasised that biases in citizen science data suggest volunteers and professionals exhibit similar patterns of errors.

However, unstructured citizen science databases should not be considered a substitute for structured monitoring data. The former lacks the sensitivity to detect population changes, thereby failing to serve as an effective early warning system for population declines, which is a crucial function of structured monitoring programs (Kamp et al., 2016). Thus, a combination of citizen science and structured fieldwork is essential for comprehensive and effective biodiversity monitoring.

## Acknowledgement

I thank the different owners who gave their authorisation to conduct fieldwork on their land, as well as Linda Lee Bluet, Marianne Elisabeth Joubert and Þórður Kristinn Sigurðsson for their help and contribution.

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<figure><img src="image_14.png" /></figure>

Soumis le 17 novembre 2025

Accepté le 10 janvier 2026

Publié en ligne (pdf) le 24 janvier 2026