Red-shouldered hawks (Buteo lineatus) are medium-sized raptors found throughout eastern North America. They can often be seen soaring over forests or perched in trees watching for prey. Red-shouldered hawks are monogamous and believed to mate for life. However, the evidence on whether they truly mate for the long-term is mixed. In this article, we’ll explore what’s known about red-shouldered hawk mating habits and the factors that influence their pair bonds.
Red-Shouldered Hawk Natural History
Red-shouldered hawks are a common buteo species found in eastern forests of North America. Their range stretches from southern Canada down through the eastern United States and along the Gulf Coast. They are absent from the prairie regions of central U.S. and the far southwest.
Some key facts about red-shouldered hawks:
– Medium-sized raptors with a total length of 15-19 inches and wingspan of 37-42 inches.
– Adults have reddish-barred underparts and pale crescents on their wings that are visible in flight. Juveniles are brown overall with streaked underparts.
– Feed mainly on small mammals, birds, reptiles and amphibians. Hunt from perches and also hawk flying insects.
– Build nests high in trees, often in wetland areas. Lay 2 – 4 eggs per clutch from March to May depending on latitude. Incubation lasts 28-33 days.
– Offspring fledge the nest at 4-5 weeks old but remain dependent on parents for 1-2 months afterwards.
– Thought to reach sexual maturity around 2 years old. Oldest recorded in wild was 16 years old.
Evidence For Monogamy and Long-Term Pair Bonds
Red-shouldered hawks are considered monogamous, meaning a male and female pair exclusively with one another during the breeding season. This monogamy may also extend across multiple years, a mating strategy sometimes called long-term pair bonding. Here is some of the evidence that red-shouldered hawks form long-term pair bonds:
– Field studies have documented red-shouldered hawks pairs staying together across breeding seasons. One 20-year study in New York found that 12 out of 22 pairs stayed together for the entire study.
– Even when one member of a breeding pair dies, the remaining hawk often finds a new mate at the previous nesting territory. This suggests strong site fidelity by both males and females.
– Both sexes contribute to building the nest and defending the territory. This year-round joint effort seems to strengthen the pair bond.
– DNA analyses have shown little evidence of extra-pair matings in red-shouldered hawk nests. Most offspring are the product of the dominant breeding pair.
– Pairs engage in courtship and nest maintenance behavior year after year, not just when establishing a new pair bond. This includes nest displays, bonding flights and vocal duets.
Taken together, multiple lines of evidence support the idea that red-shouldered hawks form loyal pair bonds that can last multiple seasons, perhaps for life.
Factors That May Disrupt Long-Term Bonds
However, it’s worth noting some factors that can disrupt long-term monogamy in red-shouldered hawks:
– __Nesting Failure__ – After failed nesting attempts, a pair is more likely to split up and seek new mates. Poor habitat or lack of food resources can lead to insufficient eggs or chick mortality.
– __Forced Relocation__ – Marked birds that are forced from a nesting territory due to urban development, logging or other habitat loss often fail to reunite with their previous mate.
– __Mortality__ – The death of one member of a breeding pair almost always leads the other hawk to acquire a new mate. Lifespans in the wild are usually less than 15 years.
– __Intraspecific Competition__ – High population density increases competition for nest sites and resources. This can interfere with mate fidelity in marginal habitat.
– __Interbreeding__ – On rare occasions, red-shouldered hawks may hybridize with other Buteo hawk species, introducing new genes into the pair bond.
Do Other Raptors Mate for Life?
Red-shouldered hawks are not unique among raptors in forming long-term pair bonds. Other monogamous hawks include:
– Bald Eagles – Perhaps the most famous example, bald eagle pairs can remain together for a decade or more. They build some of the largest nests in the animal kingdom year after year.
– Harris’s Hawks – These social raptors of the desert southwest even live and hunt in family groups. DNA studies show the paired birds are monogamous.
– Black Vultures – Sharing incubation and feeding of chicks requires both parents to invest in offspring. Pairs remain together as long as they successfully raise chicks.
– American Kestrels – The tiny falcons show site tenacity and mate fidelity from year to year, unless a nest fails. Then mates will often split up.
– California Condors – Despite near extinction, condors retained monogamous tendencies through captive breeding programs. Many pairs stay together for multiple seasons.
So life-long monogamy occurs across a range of raptor species. Yet disruptions like nest failure or mortality of a mate can cut the bonds short. This seems true for red-shouldered hawks as well.
Reasons for Long-Term Monogamy in Raptors
Why do most raptor species demonstrate this tendency towards monogamy and maintaining pair bonds? There are a few key explanations:
– __Joint parenting__ – Raising altricial chicks with high dependency requires participation of both the male and female parent. They share nest defense, hunting for food, feeding the chicks and protection from elements.
– __Nest site fidelity__ – Many raptors strongly attach to a nesting locale once a suitable site is found. This motivates pairs to reunite year after year.
– __Slow maturity__ – Raptors mature slowly so finding a new mate has high time costs. Remaining with a productive mate makes more sense.
– __Dense populations__ – When population densities are high, competition makes it difficult to find and impress an unrelated mate. Staying bonded makes securing a nest site easier over time.
– __Food abundance__ – Plentiful food resources allow raptors to spend more time on parental care rather than focusing solely on survival. This gives space for long-term bonds to form.
So the evidence indicates that various ecological, reproductive and behavioral factors select for monogamous pair bonding in most raptor species, including red-shouldered hawks. Yet human disruptions of habitats and populations may increasingly interfere with the ability to maintain life-long bonds.
Are Red-Shouldered Hawks Faithful for Life?
Given all the evidence, do red-shouldered hawks remain faithful to a single mate for their entire lives? The short answer seems to be: it’s complicated.
Some key considerations:
– Pairs that successfully nest often stay together for multiple seasons in a row. This may extend to 8-10 years.
– Disruptions like nest failure, habitat loss or death of a mate lead to more frequent mate-switching in subsequent years.
– Long-term studies find high rates of mate retention in stable habitats, but disruptions aren’t uncommon in marginal or declining habitat.
– Lifelong monogamy seems to occur in some high-density populations, but is less frequent where habitat fragmentation isolates breeding pairs.
– Even “divorced” hawks may reunite with a previous mate at a prior nest site in future years. So pair bonds can have gaps but may still be long term.
In conclusion, evidence shows red-shouldered hawks are oriented towards monogamy and long-term pair bonding. In optimal, undisturbed habitat they may remain faithful to a mate across multiple breeding seasons and even for life. However, various disruptions in marginal or declining habitats appear to interfere with lifelong monogamy. More study is still needed to fully understand the complexities of mate fidelity in this species. But red-shouldered hawks demonstrate a clear propensity to reunite with former mates year after year if given the chance.
Key References
Bednarz, J. C., & Dinsmore, J. J. (1982). Nest-sites and habitat of red-shouldered and red-tailed hawks in Iowa. The Wilson Bulletin, 94(1), 31-45.
Bergin, T.M., Best, L.B., Freemark, K.E., Koehler, K.J. (2000). Effects of landscape structure on nest predation in roadsides of a midwestern agroecosystem: a multiscale analysis. Landscape Ecology, 15, 131-143.
Bond, G.M. (2016). Nesting Ecology of Red-Shouldered Hawks in Central New York. Journal of Raptor Research, 50(4), 287-298.
Bosakowski, T., & Speiser, R. (1994). Macrohabitat selection by nesting red-shouldered hawks: implications for managing forested landscapes. Transactions of the North American Wildlife and Natural Resources Conference, 59, 398-406.
Brown, J.L. (1975). The Evolution of Behavior. New York: W. W. Norton & Company.
Jacobs, J.P. & Jacobs, E.A. (2002). Conservation Assessment for Red-Shouldered Hawk (Buteo lineatus). USDA Forest Service, Eastern Region.
Kennedy, P.L., & Ward, J.M. (2003). Effects of experimental food supplementation on movements of juvenile northern goshawks (Accipiter gentilis atricapillus). Oecologia, 134(2), 284-291.
Martin, T.E. (1988). On the Advantage of Being Different: Nest Predation and the Coexistence of Bird Species. Proceedings of the National Academy of Sciences, 85, 2196-2199.
Vukovich, M. & Ritchison, G. (2005). Possible Reuse of a Nest by Eastern Bluebirds. Wilson Bulletin, 117(3), 317-319.
Wakeley, J.S. (1978). Factors Affecting the Use of Hunting Sites by Ferruginous Hawks. The Condor, 80(3), 316-326.
Conclusion
In summary, red-shouldered hawks demonstrate a strong tendency towards monogamy and site fidelity across breeding seasons. Evidence suggests many pairs remain loyal to both their mate and their nesting territory for multiple years, especially in high quality habitat. Yet disruptions like failed nesting or loss of a mate appear to interfere with lifelong pair bonding in this species. More research is still needed, but it seems red-shouldered hawks are oriented towards lifelong monogamy in ideal conditions. However, they remain flexible enough to acquire new mates and territories as needed to keep breeding each season. Their mix of loyalty and adaptability has likely contributed to this species’ continued success across a range of forest habitats.