Bridging Continents: The Expansion and Establishment of the House Bunting (Emberiza sahari) from North Africa to Europe

Simple Summary

The House Bunting, a passerine originally from North Africa, has recently been found breeding in southern Spain. This study documents, for the first time, the presence, breeding activity, and signs of rapid population growth of this species in Europe and presents the results of a survey conducted in December 2024 to assess its local abundance and distribution in the city of Algeciras. A team of observers counted at least 18 individuals, including young birds. These birds were mainly found in low-rise buildings with flat roofs, similar to the habitats they occupy in Morocco. Their arrival in Spain is probably part of a broader trend of African birds moving into Europe, likely influenced by global warming. While their presence does not currently pose ecological concerns, they may interact with local bird species in ways that require further study. Understanding how and why species expand their ranges is important for predicting future changes in biodiversity. Monitoring this new population over time will provide valuable insights into how birds adapt to new environments and how climate change is affecting wildlife. This information can help guide conservation efforts and improve our ability to respond to changes in species distributions.

Abstract

Range expansions driven by global warming are increasingly documented, particularly in birds and insects. The House Bunting, a species native to North Africa, has recently established the first confirmed breeding population in mainland Europe in Algeciras, southern Spain. This study presents the results of the first systematic survey of this population, conducted in December 2024. Using a standardized survey method across a grid of hexagonal sampling units, we recorded a minimum of 18 individuals, including juveniles, indicating both successful reproduction and possible new arrivals. Observations were concentrated in low-rise urban areas, mirroring the species’ preferred habitats in Morocco. The presence of individuals with juvenile plumage in December suggests an extended breeding season, which may facilitate population growth. Given the geographical proximity to North Africa and predicted increases in aridity due to climate change, further expansion into Iberia appears likely. Although no immediate ecological impacts have been detected, the potential for interactions with resident species justifies continued monitoring. This study provides a baseline for assessing the establishment and growth of this population, contributing to a broader understanding of how climate change influences species distributions and the colonization dynamics of expanding bird populations.

1. Introduction

Range expansion in response to climate change has become a well-documented phenomenon over recent decades [1,2], particularly in highly mobile taxa such as birds [3,4]. These shifts are especially significant in regions serving as biogeographic barriers, such as the Strait of Gibraltar [5,6]. This natural barrier separates the African and European faunas, yet it simultaneously facilitates migration and the colonization of new areas under favourable environmental conditions [7,8].

Among the African species recently expanding their range northward, the House Bunting (Emberiza sahari) stands out [4]. This species has historically been confined to North Africa but has demonstrated a remarkable northward expansion in recent decades, reaching the north of Morocco and establishing breeding populations in the early 21st century [9,10,11,12]. Similarly, recent observations indicate an ongoing northward expansion in Algeria, particularly in the northern and high-plateau regions [13]. Records of individual vagrant birds in southern Spain date back to the late 20th century [14], with a noticeable increase in records, still of single individuals, since 2021 [15]. The breeding of the species in southern Spain was predicted in May 2023 [16] and was later confirmed for the first time in August of the same year [17]. This event not only marks the species’ arrival on a new continent but also highlights its ability to establish a new breeding population while utilizing urban habitats similar to those in Morocco.

Monitoring this newly established population provides a unique opportunity to gain insights into colonization dynamics and range expansion under the influence of climate change. Although the House Bunting is not currently threatened and does not raise immediate conservation concerns, its establishment in Europe may contribute valuable information for understanding how environmental shifts influence species distributions. Furthermore, this colonization may lead to novel ecological interactions, including competition or hybridization with resident species, as has been observed in other recently established African bird species in Europe [5,18,19]. Despite the recent nature of its establishment, the breeding population of House Bunting in Algeciras appears to be growing, likely supported by the arrival of new individuals from Africa. This influx of individuals could facilitate rapid population growth, potentially enabling the species to spread further into continental Europe. At this early stage of colonization, the population remains relatively concentrated, providing a unique opportunity to estimate changes in the number of individuals over time. Such estimates are crucial for understanding the demographic processes driving this expansion and for evaluating the factors that influence its success, which is essential for advancing our knowledge of colonization dynamics under changing climatic conditions.

This study documents and analyses, for the first time, the presence, breeding, and signs of rapid population growth of the House Bunting in Europe, focusing on the population established in Algeciras (southern Spain) since 2023. Rather than conducting a formal census, our aim is to highlight the species’ expansion and demographic momentum in this newly colonized area. The study also explores the biogeographic and ecological implications of this colonization, highlighting the potential for further growth and the importance of long-term monitoring to better understand the population dynamics of expanding species and avian responses to climate change.

2. Material and Methods

2.1. Study Area

The study was conducted in the urban area of Algeciras, a city in southern Spain where the House Bunting has recently established the first breeding population in mainland Europe. Algeciras is the largest city in the Bay of Algeciras, with approximately 123,000 inhabitants, and it features a mix of residential, commercial, and industrial areas. The city has a Mediterranean climate with mild, wet winters and warm, dry summers.

Breeding was first confirmed in September 2023, when a juvenile was observed begging for food from an adult, followed shortly by the detection of a second chick in the same area [17]. The survey focused on this neighbourhood and its surroundings, including residential districts with a high density of buildings. This study area is located near the harbour of Algeciras, one of the largest and most important ports in the Mediterranean, which could have facilitated the arrival of individuals here either partially or entirely via ship-assisted dispersal, as has been described for many other passerine species [20]. The city is located approximately 24 km from the African continent, where the species already has stable populations in northern Morocco, as well as in the Spanish city of Ceuta (Figure 1).

2.2. Study Species

The House Bunting is a small passerine native to northwestern Africa. Notable for its subtle plumage and distinctive behaviour, it inhabits rocky and arid environments but is also strongly associated with urban areas, nesting in walls and other man-made structures, and is often seen entering buildings [11]. The species is largely resident across its range, which includes Morocco, Algeria, Tunisia, Mauritania, and western Libya, as well as scattered occurrences in the Sahel [21]. Since the mid-20th century, a progressive northward expansion has been documented, particularly in Morocco and Algeria, where it has reached the Mediterranean coast and crossed the Strait of Gibraltar [11]. Breeding was confirmed in southernmost Spain (Algeciras) in 2023 [17] and 2024. In Morocco, the species breeds almost year-round, with a season extending from January to October, with peaks in spring and midsummer and with pairs frequently raising multiple broods per year [11].

2.3. Survey Methods

The survey was conducted on 14 December 2024 from sunrise to two hours after (8:00 to 10:00 local time), with a total of 15 observers surveying the area. All observers are experienced ornithologists with extensive field knowledge, including familiarity with the target species. Although this survey was conducted outside the main breeding season, House Buntings maintain territorial behaviour year-round, and their song—distinctive and easily recognizable to trained observers—can be heard even in winter. To account for potential variations in detectability during this period, we expanded the survey area beyond the core breeding zone, ensuring a more comprehensive assessment of the population. As only a year has passed since the species was first confirmed breeding in the area, its establishment remains at a very early stage. Nevertheless, in the case of the House Bunting, the winter survey has been valuable, as it allowed us to detect the presence of both adults and juveniles and provided a snapshot of population growth, offering key insight into the species’ range expansion, successful local reproduction, and its potential to establish stable populations in newly colonized areas.

2.4. Data Preparation

Uber’s H3 spatial indexing system [22] was used to design the sampling zones for the bird census. The study area was divided into 233 H3 equal-sized hexagons at resolution 11, 2281 m² each (Figure 2, Supplementary Material), which were surveyed to ensure comprehensive coverage. The use of hexagons is particularly advantageous for spatial analysis, as this geometric shape allows for uniform coverage and facilitates the application of analytical methods by ensuring a comparable sampling effort across the study region. While the hexagonal grid provided a systematic framework, the final selection of hexagons to be surveyed was conditioned by habitat availability and accessibility. Specifically, we prioritized hexagons overlapping with urban areas offering suitable breeding habitat for the species, particularly in and around the neighbourhood where breeding was first confirmed. This systematic approach not only enhances the reliability of the data collected but also facilitates the analysis of results from future censuses, enabling consistent comparisons over time and a better understanding of temporal trends and spatial patterns.

The area encompassing all observations was determined using a convex hull approach based on the geographic coordinates (latitude and longitude) of all observation points. This method computes the smallest convex polygon that encloses all observation points, ensuring a robust estimate of the spatial extent of the recorded locations.

Observers spent between four and eight minutes in each hexagon, with an average of five minutes, focusing on detecting the species’ songs and calls, as well as direct visual observations. While the survey protocol aimed to maintain a consistent observation time across hexagons, slight variations were unavoidable due to differences in building height and architectural complexity. In some areas, taller structures or irregular urban layouts required more time to adequately scan rooftops and upper building fronts, where individuals of the species frequently perch. For each contact with the species, observers recorded the coordinates, time, number of individuals, and, when possible, the age and sex of the birds. Prior to the survey, all participants were instructed to identify the species both acoustically and visually to ensure consistency in data collection. Despite the observers’ expertise, specific training was considered essential due to the recent arrival of the House Bunting in the area. This was further justified by the narrowness of the streets within the survey area, the behavioural patterns of the species, such as its tendency to be found on rooftops and upper parts of buildings, and its relatively low detectability.

3. Results

The total number of observations analyzed was 25, with a minimum of one and a maximum of six birds observed per event. The average number of birds per observation was calculated as 1.4 (SD = 1.04). The cumulative sum of birds across all observations amounted to 35 individuals. After analyzing the data and adjusting for both the timing and coordinates of each observation to prevent double counting, the minimum number of birds was estimated at 18. This conservative estimate ensures a more accurate representation of the population, accounting for potential overlaps in observations due to their spatial and temporal proximity. The area occupied by the observations was calculated as approximately 0.47 km², and the maximum distance between observation points was 1745 m.

The observations were distributed across 16 hexagons, with most detections occurring in the neighbourhood where breeding was first confirmed in 2023 (Figure 3). We recorded birds in areas where the species had not been detected before, particularly in areas of the city closest to the port. The spatial distribution of all records illustrates a concentration of detections in low-rise buildings and flat roofs (Figure 3). No individuals were recorded in non-urban or industrial areas. We observed individuals in adult plumage, as well as some individuals still in juvenile plumage.

4. Discussion

4.1. Biogeographical Significance of Colonization

The establishment of the House Bunting in southern Spain represents a significant biogeographical event, marking the first confirmed breeding population of this species in mainland Europe and evidence of its local establishment and population growth. Following earlier records of individual birds, it was in September 2023 when the first breeding event of the species was detected, with a pair raising two chicks [17], and by December 2024, the population has grown to at least 18 individuals. This growth suggests both successful reproduction and the potential arrival of new individuals. The geographical proximity between Morocco and Spain, with the shortest distance across the Strait of Gibraltar being just 14 km, likely facilitated the dispersal of the House Bunting. However, despite the short distance between the African continent and the city where the species is established, it is also important to consider the proximity of the breeding nucleus to a major commercial port. This port operates daily crossings connecting Algeciras with North African cities where the species is already present, potentially contributing to its arrival and establishment. This highlights the importance of physical connectivity in enabling biogeographical transitions [23,24]. With respect to their possible origin related to pet ownership, there is no evidence suggesting any degree of domestication in the observed individuals. The behaviour of House Buntings in Algeciras is identical to that observed in Moroccan cities where the species has been established for decades, such as Marrakech, Essaouira, or Casablanca (pers. obs.), where they commonly approach areas where food is provided by humans.

4.2. Climatic Drivers of Expansion

Climate change models predict increased climatic favourability in the southwestern quadrant of the Iberian Peninsula [4,16], suggesting that the region could provide suitable conditions for the species’ continued expansion. This colonization aligns with broader trends of natural range expansions by African species, such as the Black-winged Kite (Elanus caeruleus) and the Little Swift (Apus affinis), which have also established populations in Iberia in recent decades [25,26], and also with future predictions of increasing colonization by North African species as climatic and ecological conditions in southern Europe become progressively more favourable [4].

4.3. Urban Adaptation and Ecological Flexibility

The ability of the species to utilize urban habitats in Spain, like those it occupies in Morocco [11], may also have contributed to its successful establishment. The urban area selected for colonization in Algeciras is structurally the most similar to the breeding sites used in Morocco, consisting primarily of a densely populated neighbourhood with low-rise buildings, flat roofs, and inner courtyards, which provide suitable nesting sites. These areas also offer consistent food availability, further supporting the species’ establishment. Urban environments reduce predation risks [27] and provide a favourable ecological setting for colonization [28]. This ecological flexibility highlights the importance of anthropogenic habitats in enabling range expansions, particularly for species already adapted to human-altered landscapes.

Notably, the observation of birds with fresh juvenile plumage in December (Figure 4) suggests that the House Bunting may also breed in autumn. Typically, birds hatched in spring moult into adult plumage by October [29]. Therefore, the presence of individuals with juvenile plumage in December indicates a longer breeding season compared to native species like the House Sparrow, whose breeding activity is usually confined to the spring and summer months. This extended breeding period could provide the House Bunting with an adaptive advantage in its colonization process, allowing for increased offspring production throughout the year and facilitating its establishment in new areas. If similar dynamics occur in Algeciras, as observed in coastal cities like Ceuta (Spain) and Fnideq (Morocco), both located on the northern coast of Africa, where the House Bunting is now a common species, the population is likely to grow further. Algeciras could then serve as a source population for colonizing nearby cities, such as Los Barrios, San Roque, Gibraltar, or La Línea, among others.

Although the House Bunting primarily occupies urban habitats, its presence could still have ecological implications. Potential interactions include competition with the House Sparrow (Passer domesticus), which shares the same urban environment, and possible contact with the Rock Bunting (Emberiza cia). Despite their taxonomic proximity, there is no evidence of hybridization between these two species, likely due to differences in habitat preference and breeding phenology. Similar dynamics have been observed in other African species, such as the Long-legged Buzzard (Buteo rufinus cirtensis) [6] and Rüppell’s Vulture (Gyps rueppelli) [30], where successful integration into local communities has depended on habitat overlap and ecological compatibility. These interactions, although subtle, could influence community structures and trophic networks in the region, warranting further investigation.

4.4. Future Prospects and Study Limitations

Climate models predict increasing aridity in Spain [31], which could further facilitate the expansion of North African species, including the House Bunting. As suitable niches emerge due to climatic shifts, Iberian biodiversity may undergo significant changes, with new colonists potentially altering ecological balances. The House Bunting’s establishment underscores how climate change can reshape faunal distributions, providing opportunities for North African species to exploit new habitats in southern Europe.

Our study has some limitations, including its single-day survey and single-season dataset, which may constrain broader inferences about population trends and seasonal dynamics. Nonetheless, this one-day snapshot, obtained less than a year and a half after the species was first confirmed breeding in the area, already reveals a population of at least 18 individuals, some of them juveniles, which strongly suggests a remarkable demographic growth in a short time frame. This is particularly relevant given the recent nature of the colonization and supports the idea that the species is not only established but may be in the early stages of a significant expansion. The presence of juveniles in December indicates continued reproductive activity well beyond the typical breeding season, further reinforcing this idea. In this context, our findings provide a valuable snapshot of a continental colonization process in its initial stages, offering valuable insights into how the House Bunting is establishing itself in mainland Europe.

Given the novelty of this colonization, long-term monitoring will be essential to understand the population dynamics of the House Bunting, its expansion, and potential ecological impacts. Systematic surveys and the use of citizen science platforms could strengthen monitoring efforts, improve predictions of future expansions, and enhance our understanding of avian responses to climate change and the processes underlying range expansions in a rapidly changing world.