Short-eared owls (Asio flammeus) are medium-sized owls found throughout the Northern Hemisphere. They prefer open habitats like grasslands, marshes, and agricultural fields. Short-eared owls are known for their buoyant, moth-like flight. Their distinctive ear tufts are usually not visible.
Short-eared owls are crepuscular and nocturnal hunters. Their diet consists mainly of small mammals like voles, mice, and rabbits. They also eat birds, reptiles, amphibians, and large insects. Short-eared owls hunt by flying low over open ground and dropping down on prey.
The nesting habits of short-eared owls are somewhat unique among owls. They do not use cavities or tree nests. Instead, short-eared owls nest on the ground, typically in dense grassy cover. The female scrapes out a shallow depression and lines it with grasses, feathers, and fur. Short-eared owls are loosely colonial nesters and may have their nests relatively close together when prey is abundant.
Territorial behavior is when animals actively defend an area against intruders of the same species. Territoriality serves to provide exclusive access to resources like food, nest sites, and mates. Territorial behavior often involves agonistic displays like vocalizations, aggressive postures, and even physical combat.
Do short-eared owls defend nesting territories?
Whether short-eared owls vigorously defend distinct nesting territories is somewhat unclear based on available research. Some sources indicate they are territorial around the immediate nest site. Other evidence suggests short-eared owls have more loosely defined nesting ranges and may tolerate conspecifics nesting relatively close by.
Several factors make definitive territory boundaries difficult to discern in short-eared owls:
– Their home ranges are large, varying from around 270 acres up to over 6,000 acres.
– Short-eared owl nests can be loosely clumped together when prey is abundant. Internest distances may range from around 50 yards up to 0.6 miles.
– Individual owls do not necessarily return to the exact same nest site every year.
– Agonistic displays between short-eared owls around the nest have been observed but appear relatively infrequent compared to other territorial owl species.
Overall the available data suggests short-eared owls are somewhat territorial around the nest when conditions allow. However, they are probably more flexible than most owls when it comes to tolerated neighbor distances and site re-use. Dense prey availability enables closer nest clustering and reduces territorial pressures.
Do short-eared owls defend hunting territories?
The evidence is stronger that short-eared owls defend hunting territories during the non-breeding season. Multiple research studies have shown short-eared owls will establish fixed hunting ranges and chase intruders out of those areas.
In one radio-telemetry study conducted on the small island of Flatey in Iceland, researchers found wintering short-eared owls held stable hunting territories averaging around 100 acres in size. The territories showed little overlap, indicating their borders were being actively maintained.
Other observations of territorial behavior in wintering short-eared owls include:
– Advertising territorial boundaries with flight displays and vocalizations.
– Aggressive responses to perceived intruders, including aerial attacks.
– Returning to the same hunting grounds over multiple seasons.
So while they may be somewhat flexible with nest spacing, short-eared owls appear to actively maintain distinct hunting ranges in winter when prey is limited. These hunting territories likely provide better access to resources and reduce competition from other owls.
How do territory sizes vary by location?
The size of short-eared owl hunting territories varies substantially based on habitat and prey availability in a given location. Some key factors influencing territory size include:
– **Prey density** – When voles and other prey are abundant, territories can be relatively small. In poor prey years, territories expand in search of resources.
– **Habitat** – Open habitats like grasslands and marshes allow smaller territories than patchy woodland habitats. More navigable terrain is easier to defend.
– **Breeding vs. nonbreeding season** – Nonbreeding season territories are typically larger than breeding season ranges.
– **Nesting density** – High nest density corresponds to smaller breeding season territories.
– **Population density** – High owl density leads to increased competition and smaller territories.
Various territory size ranges have been reported from different locations:
– Iceland – Average of 100 acres in winter.
– Scotland – 115 to 230 acres in winter.
– Netherlands – Over 1000 acres in winter.
– Idaho – Approximately 270 acres during nesting.
– Saskatchewan – Up to 6400 acres during nesting when prey was scarce.
So short-eared owl territories can be as small as 100 acres when prey is plentiful or as large as several square miles when resources are scarce. Population density also plays a key role.
How do short-eared owls communicate territory boundaries?
Short-eared owls use various signaling behaviors to advertise and defend their territories from intruders and rivals:
– **Flight displays** – Dramatic flight performances help mark territorial boundaries. These aerial shows involve hovering, slow fluttering flight, and undulating dives.
– **Vocalizations** – Short-eared owls have a wide repertoire of barks, rasps, and screams used when defending territories.
– **Aggressive approaches** – Intruders into a territory may be physically chased and dive-bombed. Aerial battles can ensue.
– **Scraping** – Owls reinforce territory ownership by scraping depressions in the ground, possibly visually marking the area.
– **Perch occupation** – Prominent perches are frequently occupied as sentinel posts overlooking the territory.
So short-eared owls use both visual displays and vocal signaling to advertise territories. Direct aggressive contact serves to repel rivals and prevent intrusions by neighboring owls.
Conclusion
In summary, the available evidence suggests short-eared owls do exhibit territorial behavior, particularly during the non-breeding season when prey is limited. Their large hunting ranges are actively defended through displays and aggression.
Breeding season territoriality appears more flexible, with owls tolerating relatively close nest spacing when prey is abundant. However, some defense of the immediate nest vicinity likely still occurs.
Territory size can vary substantially based on location, prey availability, season, and population density. Short-eared owl territories may range from as small as 100 acres to over 6000 acres.
Unique signaling behaviors like aerial displays, vocalizations, and ground scraping help short-eared owls mark and communicate their territory boundaries to rivals. Defense through direct approaches and attacks helps maintain exclusive access to the resources within those territories.
