Plain language summary
This study explores the diet of the Short-eared Owl (Asio flammeus) in central Israel. It shows that the owl mainly relies on rodents, especially Günther’s vole, for food, with mammals making up to 98.2% of its diet. We analyzed 260 pellets and found 385 prey items, mostly small mammals. The research stresses the need to protect both the owls and their rodent prey in a changing environment.
Abstract
This study investigates the dietary habits of the Short-eared Owl (Asio flammeus) in central Israel, highlighting its reliance on rodent populations, particularly Günther's vole (Microtus guentheri), as a primary food source. In 260 pellets, we identified 385 individual prey items, with mammals constituting 98.2% of the diet, underscoring the owl's almost exclusive dependence on these small mammals for sustenance. The average weight of the analyzed pellets was 3.3 grams (+ 1.11 SD), with a significant majority of the biomass derived from rodent prey. Our findings reveal that the Short-eared Owl exhibits opportunistic breeding behaviors, migrating in response to prey availability and occasionally breeding outside its known range when conditions are favorable.
Introduction
Short-eared Owl (Asio flammeus) is currently classified as a species of Least Concern by the International Union for Conservation of Nature (IUCN), primarily due to their extensive geographic distribution across various regions of the world (Birdlife International 2021). Despite this relatively secure classification, it is important to note that populations of Short-eared Owl have experienced significant declines in certain areas, a trend that can be attributed mainly to habitat loss and the degradation of grassland ecosystems.
The species boasts a wide array of locations across North and South America, as well as Europe, Africa, and parts of Asia, while notably excluding the continents of Antarctica and Australia (Mikkola 1983). Within Israel, Short-eared Owls (Fig. 1) are classified as a non-breeding species (Israel Bird Base 2024), yet the Israel Red List (2024) identifies them as Critically Endangered. This classification is due to the presence of a small, sporadically breeding population consisting of fewer than 50 adults reported in the past (Shirihai 1996). Historical breeding observations of this owl species in Israel are not only rare but also largely incidental, highlighting the precarious status of these birds in the region.
Short-eared Owl Asio flammeus perched on the ground and in flight in the fields in central Israel. Photos Ezra Hadad.
Citation: Israel Journal of Ecology and Evolution 71, 3 (2025) ; 10.1163/22244662-bja10103
Overall, the Short-eared Owl represents a species of ecological importance and conservation concern. The lack of comprehensive information about this species across many parts of its distribution further emphasizes the urgency of these efforts, especially outside its major breeding distribution.
Unlike many other owl species, Short-eared Owls are primarily crepuscular and even exhibit diurnal behavior, frequently hunting during the day or at dusk. These owls are known for their distinctive hunting style, flying low over open fields and marshes as they search for prey (Korpimaki and Norrdahl 1991, Reid et al., 2011). They rely heavily on their exceptional eyesight and acute hearing to detect potential food sources, which mainly consist of small mammals (König and Weick 2008).
Short-eared Owls consume prey whole, swallowing small animals, and later regurgitating indigestible materials as pellets (Newton 2002, Wiggins et al., 2020). They are opportunistic feeders, adapting their diet to available prey (Williford et al., 2011, Cullen et al., 2012). Pellet analysis is a common method for studying their diet, though it has biases (Yom-Tov and Wool 1997, Redpath et al., 2001). Pellets over-represent smaller prey, while prey remains over-represent larger species. Combining these methods doesn’t eliminate biases, though biomass estimates may be more accurate (Hadad et al., 2022a).
Despite their extensive global distribution, the majority of studies examining the diet of Short-eared Owls have predominantly focused on populations in North America and Europe (Leasure and Holt 1991, Rau et al., 1992). Quantitative data specifically pertaining to their diet in the Middle East is notably sparse, with the existing research primarily limited to Türkiye (Güngör et al., 2021).
In Israel, the phenomenon of rodent population explosions, especially in agricultural fields, is well-documented. These surges often occur following poisoning events that are implemented to control such outbreaks (Mendelssohn and Paz 1977). In the Judea region, agricultural development has contributed to periodic increases in rodent populations, particularly featuring species such as the Levant (Günther’s) vole (Microtus guentheri; Fig. 2), Tristram’s jird (Meriones tristrami), and house mouse (Mus musculus) (Hadad 2019, Hadad et al., 2022b).
A typical agricultural field with rodent burrows and a Levant vole (Microtus guentheri) in central Israel. Photos Ezra Hadad.
Citation: Israel Journal of Ecology and Evolution 71, 3 (2025) ; 10.1163/22244662-bja10103
During the winters of 2015 and 2016, these rodent outbreaks reached exceptionally high densities. This significant seasonal rodent outbreak, occurring over two consecutive winters, provided the conditions necessary for opportunistic breeding by three pairs of Short-eared Owls (Hadad 2019).
As many as 30 Short-eared Owls, representing the largest concentration ever recorded in Israel, roosted and foraged in these agricultural fields, with three pairs successfully breeding in close proximity the following spring (Hadad et al., 2022b). In the winter of 2015–2016, 30 short-eared owls wintered in the Judean Plain. A particularly large concentration of 20 individuals wintered in the Kdema excavation area, seven others wintered in the Zohar reservoir area, and three wintered in the fields of Beit Nir. In the winter of 2016–2017, 15 short-eared owls wintered in the Judean Plain. In the Kdema excavation area, eight individuals wintered; in the Zohar reservoir area, five individuals wintered; and in the Beit Nir area, two individuals wintered. This remarkable situation provided us with the opportunity to collect pellets from the roosting sites for dietary analysis. We hypothesized that the relative abundance of rodents in the surrounding fields would be mirrored in the diet of the Short-eared Owls, as has been suggested in previous studies (Stone et al., 1994, Reid et al., 2011). This correlation would allow us to gain valuable insights into the feeding behavior and ecological dynamics of these owls in relation to their prey availability.
Methods
The study took place in the Judea region of Israel, covering 2,644 km². Specific locations included Kedma (31°42’5”N, 34°46’32”E), Moshav Zohar (31°35’43”N, 34°41’32”E), and Kibbutz Bet Nir (31°38’52”N, 34°52’26”E). These sites have water bodies surrounded by marshes and grasslands, which is where the Short-eared Owls bred on the ground.
Short-eared owls were observed hunting in the roosting area and its immediate surroundings. We collected 260 pellets from the roosting sites during the winter of 2015–2016, between the dates of December 10, 2015, and March 2, 2016. In the winter of 2016–2017, the collection began on December 4, 2016, and continued until March 18, 2017. Pellets were stored individually in sealed plastic bags and cardboard cartons. We randomly weighed 68 oven-dried pellets (digital scale ± 0.01 g) and measured their length and breadth (digital caliper ± 0.01 mm). Each pellet was analyzed to identify prey species. We excluded invertebrate mass due to their small biomass compared to vertebrates, comprising only 0.8% of the diet (Table 1).
Prey species were identified in 260 pellets of wintering Short-eared Owl (Asio flammeus) in Central Israel. Ke denotes Kedma, ZR the Zohar Reservoir, and BN denotes Bet Nir.
Citation: Israel Journal of Ecology and Evolution 71, 3 (2025) ; 10.1163/22244662-bja10103
Mammalian prey identification was aided by Mendelssohn and Yom-Tov (Mendelssohn, H.; Yom-Tov, Y. 1987, 1999), with body masses referenced from Wilson et al. (2017) and Krystufek et al. (2011). Avian prey identification was based on Snow and Perrins (1998).
Results
From 260 pellets, we identified 385 prey items (Table 1), with 384 (99.7%) identified at the species level. We measured 68 pellets (26.2%), finding an average mass of 3.3 g (± 1.11 SD, range 1.0–4.77), average length of 57.8 mm (± 16.2, range 23.8–87.8), and average breadth of 19.9 mm (± 2.36, range 13.3–25.2).
Most prey items were mammals (N = 378, 98.2%; Table 1), with only four birds (1.0%) and three arthropods (0.8%). Mammals made up 99.3% of the biomass, while avian prey accounted for 0.7%. Levant vole dominated the diet, representing 87.3% (N = 336) of prey items and 91.7% of the total biomass.
Discussion
Our study uncovers the significant dependence of Shorteared Owls on rodent populations, which plays a crucial role in supporting their breeding success in regions characterized by a high abundance of prey. This opportunistic behavior is particularly noteworthy; the owls migrate to different locations when their primary food sources are scarce, yet they choose to breed in areas where prey is plentiful. The dominance of small mammals, particularly rodents, in the diet of Short-eared Owls, is well-documented across various studies. For instance, in southern South America, rodents constituted 80.0% of their diet (Rau et al., 1992), while in Hawaii, it rose to 83.1% (Wang 2022). In Colombia, 75.2% of their diet comprised rodents (Restrepo-Cardona et al., 2021), and in Massachusetts, the percentage was 83.0% during the breeding season and a staggering 95.0% during the non-breeding season (Holt 1993). Further evidence from Bulgaria and Romania shows that 78.49% and 99.4%, respectively, of their diet consisted of small mammals (Simeonov 1983, Ionescu et al., 2017). In Yukon, Canada, this number was similarly high at 99.0% (Reid et al., 2011). In western Siberia, rodents made up 100.0% of their dietary intake (Dupal and Chermyshov 2013), while in northwestern Turkey, this figure was 95.4% (Güngör et al., 2018). In Baluchistan, Pakistan, small mammals constituted 96.7% of their diet (Mushtaq-ul-Hassan et al., 2007), and in Maharashtra, India, they accounted for 81.0% (Jathar et al., 2011).
Despite this heavy reliance on rodents, Short-eared Owls also demonstrate a remarkable degree of dietary flexibility. For example, in regions where rodents are not readily available, such as certain islands, these owls adapt their feeding habits by preying on alternative sources like rabbits (Oryctolagus cuniculus; 60.8%) and petrels (Pterodroma spp.; 19.6%), as observed in the Juan Fernández Archipelago in Chile (González-Acuña et al., 2023). In Algeria, the situation is different; here, rodents constituted only 28.5% of their diet by number and 26.9% by biomass, while birds accounted for a significant 52.0% of biomass, alongside contributions from amphibians (11.4%), reptiles, and insects (Djilali et al., 2016). In Andhra Pradesh, India, wintering Short-eared Owls exhibited a preference for birds, which made up a remarkable 86.3% of their diet, with mammals being a secondary food source at 10.3% (Srinivasulu and Srinivasulu 2007). Additionally, in Toronto, Canada, Short-eared Owls primarily targeted migratory birds, even in the presence of voles (Munro 1918). This adaptability highlights the owls’ ability to adjust their foraging strategies in response to the availability of different prey types.
A particularly notable prey item for the Short-eared Owl is Kuhl’s pipistrelle (Pipistrellus kuhlii), especially given that bats are infrequently observed in the diets of these owls (Sieradzki and Mikkola 2020). However, there is an intriguing exception documented in Algeria, where bats accounted for a substantial 39.4% of the total prey items consumed by Short-eared Owls, albeit representing only 9.3% of the total biomass (Djilali et al., 2016). This discrepancy suggests that while bats may be caught frequently, they do not provide a significant amount of energy relative to their hunting costs. The low energetic cost-benefit ratio associated with hunting bats likely explains their overall exclusion from the typical diet of Short-eared Owls in most regions.
Our study also revealed that the dimensions of owl pellets vary significantly across different geographical areas. In our research, we recorded an average pellet length of 57.8 mm and a breadth of 19.9 mm. Djilali et al. (2016) conducted similar measurements and found that their study revealed an average pellet length of 39.2 mm (± 8.8, with a range from 23 to 75 mm) and a width of 25.7 mm (± 4.8, with a range from 15 to 41 mm). In Maharashtra, India, the average dimensions were somewhat smaller, with an average length of 34.0 mm (± 8.7) and a breadth of 16.4 mm (± 3.3) (Jathar et al., 2011). These variations in pellet dimensions may reflect differences in prey availability, individual variability, hunting strategies, and environmental conditions across regions. Owl selection, capture, and ingestion of prey can affect pellet dimensions. For example, owls that capture larger or multiple prey items in a single hunting bout might produce larger pellets due to the increased volume of indigestible material. Conversely, a strategy focused on smaller or more easily digestible prey might lead to smaller pellets. Environmental conditions such as habitat structure, climate, and prey availability can indirectly affect pellet dimensions by influencing prey diversity and abundance. In areas where environmental conditions favor a higher diversity of prey, owls may consume a broader range of prey sizes, which could result in variations in pellet size and composition. While our study suggests a relationship between pellet dimensions and these factors, we acknowledge that the current literature provides limited information. Our findings highlight potential avenues for future research to elucidate the mechanisms behind these observations better.
Conclusions
Our findings further indicate that during the significant rodent outbreak in the agricultural areas of Judea in the winters of 2015 and 2016, Levant vole (Microtus guentheri) emerged as the dominant prey species, comprising an impressive 87.3% of the total prey items and contributing 91.7% of the total biomass.
This study underscores the critical dependence of Short-eared Owls on rodent prey for successful wintering and even breeding in central Israel.
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