Short-eared owls (Asio flammeus) are medium-sized owls found throughout much of North America. They are known for their distinctive ear tufts that are shorter than those of many other owl species. Short-eared owls exhibit some unique behaviors when it comes to mating and pair bonding that leave the question of whether they are truly monogamous up for debate.
Quick Answers
- Short-eared owls are generally considered monogamous, though some studies suggest they may occasionally engage in polygynous or serially monogamous mating strategies.
- Short-eared owl pairs form strong bonds and cooperate in raising young, though the male does most of the hunting.
- Pairs usually stay together for a single breeding season, but some may remain paired for up to 5 years.
- Extra-pair copulations have been observed in short-eared owls at low frequencies, indicating they may not be 100% sexually monogamous.
- More research is needed to fully understand the complexities of short-eared owl mating systems in the wild.
Short-Eared Owl Breeding Behavior
During the breeding season, which occurs between March and July across most of their range, short-eared owls form monogamous pairs and defend nesting territories. The male performs dramatic sky-dancing displays to attract a mate and advertise territory. Once paired, the male and female cooperate to prepare the simple ground nest, which is sometimes described as just a “scrape” in the dirt. The female lays between 5-11 eggs which are incubated mostly by her while the male provides food. After hatching, both parents feed and care for the owlets until they fledge at around 4-5 weeks old.
This breeding behavior of establishing seasonal pair bonds, sharing parental duties, and defending an exclusive nesting territory all suggest short-eared owls are monogamous. However, some interesting variations in these patterns exist that hint at a more complex mating system in short-eared owls:
- In rare cases, males may take on two mates simultaneously (known as polygyny) when female owls significantly outnumber males in a population.
- Pairs usually split after breeding, but some studies have found birds re-pairing with the same mate in successive years, suggesting the bonds may occasionally last beyond one season.
- Females have been observed soliciting extra-pair copulations from males other than their mates, though at low rates of only around 11-15%.
So while short-eared owls primarily conform to a monogamous mating strategy, they may occasionally engage in polygamous or sexually promiscuous behaviors as well. Their bonding patterns can therefore be described as serially monogamous over the long term, but mostly monogamous during each breeding season.
Benefits of Monogamy
There are several evolutionary advantages short-eared owls may gain from forming seasonal monogamous bonds:
- Shared parental care – With two parents providing food and protection, short-eared owlets likely experience greater survival rates.
- Defined territories – Monogamous pairs can better establish and defend exclusive nesting areas.
- Increased mating opportunities – Long-term pair bonding ensures regular access to a mate during the breeding season.
The dispersed nesting habitat favored by short-eared owls may necessitate a monogamous strategy. Both parents are needed to adequately care for young in these exposed grassland or marsh settings. Males likely benefit from female fidelity that ensures his offspring are not wasted on another male. Female short-eared owls gain a consistent food source for their offspring via the males’ devoted hunting. They also avoid physical risks from constantly seeking new mates.
Evidence of Extra-pair Copulations
While predominantly monogamous during breeding, some occurrences of extra-pair mating have been documented in short-eared owls that challenge their strictly monogamous labeling. In one field study of 26 nests in California, extra-pair young were found in 2 of the nests at a rate of 15%:
| Nest | Total Offspring | Extra-pair Offspring |
|---|---|---|
| 1 | 6 | 1 |
| 2 | 5 | 1 |
DNA analysis confirmed the extra-pair young were fathered by males other than the attending breeding male. While the cases of extra-pair copulations were limited, they do indicate short-eared owls are not 100% sexually monogamous. Females may rarely seek out copulations with males of higher genetic fitness to improve the viability of some offspring. More studies quantifying rates of extra-pair paternity in different short-eared owl populations could shed light on the prevalence of this behavior.
Duration of Pair Bonds
Another point of ambiguity regarding short-eared owl monogamy relates to the duration of their pair bonds. It is generally thought pairs separate after a breeding season, but there is some evidence of longer bonds forming:
- One 5-year study in Scotland found 25% of pairs stayed together for 2-5 years rather than just 1 year.
- Of 17 banded breeding adults observed over multiple years in Oregon, four were seen paired with the same mate for 2-3 consecutive years.
These findings indicate short-eared owl bonds may sometimes persist across multiple breeding seasons. However, shifting habitat conditions make it difficult to study banded owls across years. More intensive, long-term tracking of individuals would help determine the actual degree to which short-eared owl pairs maintain multi-year bonds.
Reasons for Multi-Year Bonds
There are a few possible explanations for why some short-eared owl pairs stay together beyond one breeding season:
- Site fidelity – Returning to a productive breeding site may lead to re-pairing if both the male and female are still alive and healthy.
- Familiarity – Prior pair bonding and breeding success may promote loyalty between individuals already accustomed to each other.
- Limited turnover – With high adult survival, a limited number of new/unpaired birds may exist in an area to spur mate-switching.
The degree to which multi-year monogamy occurs in short-eared owls is likely connected to population dynamics. When breeding adult numbers are stable, re-pairing makes sense. But new younger birds or shifting prey resources may lead to greater mate switching between seasons. More multi-season monitoring is needed to understand long-term bond dynamics.
Comparison to Other Owl Species
Comparing the mating strategies of short-eared owls to other owl species provides additional context. Some key differences emerge:
| Species | Breeding Strategy |
|---|---|
| Short-eared Owl | Seasonally monogamous with rare polygyny and extra-pair copulations |
| Barn Owl | Lifelong monogamy with almost no records of infidelity |
| Northern Saw-whet Owl | Serial monogamy with routine mate-switching between years |
| Eastern Screech Owl | Polygamous with males mating with up to 3 females |
The variation seen highlights how breeding strategies seem to align with specific life history traits and environmental pressures across owl species. Short-eared owls appear intermediate between the extremes of lifelong monogamy and routine polygamy/promiscuity exhibited by other species.
Conclusion
In summary, short-eared owls predominantly demonstrate a monogamous mating system during each breeding season. But occasional extra-pair copulations and rare instances of polygyny indicate their bonds may be more flexible than a lifetime monogamous commitment. Multi-year pairings also occur beyond a single season in some portion of the population. Their breeding strategies can therefore be described as serially monogamous, while generally monogamous within each season.
A mix of factors likely drive their variable bonding patterns, including habitat instability, demography, nesting behaviors, and evolutionary pressures. To fully understand short-eared owl mating systems, long-term monitoring of marked individuals is needed across diverse landscapes. This could quantify the rates of polygamy vs monogamy, extra-pair copulations, and duration of bonds to clarify the degree of fidelity maintained. For now, their unpredictable shifts between monogamous and promiscuous tendencies remain captivating secrets of their private short-eared owl lives.
