Cooper’s hawks are small but powerful accipiter hawks found throughout much of North America. They are adept hunters, specializing in catching small birds and mammals in wooded areas. Cooper’s hawks play an important role as mid-level predators in many ecosystems.
Like many bird species, Cooper’s hawks form breeding pairs during the mating season. However, there has been some debate among ornithologists about whether Cooper’s hawks mate for life, or if they form new pair bonds each breeding season.
In this article, we’ll examine the evidence regarding Cooper’s hawks’ mating habits and look at the characteristics of this species that provide clues about whether lifelong monogamy is part of their reproductive strategy. We’ll also discuss the evolutionary factors that may influence mating systems in birds of prey.
What Does “Mating for Life” Mean for Birds?
When we say a bird “mates for life,” it generally means that adult birds form durable pair bonds that extend across multiple breeding seasons, though not necessarily for their entire lifespan. Some species like albatrosses and swans are known to mate with only one partner until one of the pair dies.
However, lifelong monogamy with absolute fidelity is extremely rare, even among so-called “monogamous” species. Birds may remain paired for life, but still occasionally seek extra-pair copulations outside the primary partnership. There is a spectrum of monogamous behaviors in birds ranging from serial monogamy (forming new pairs each season) to long-term pair bonds with occasional infidelity.
Cooper’s hawks are seasonally monogamous, meaning they form breeding pairs during the mating season. The key question is whether those pairs consistently reform in subsequent years, or if the hawks seek new mates each season.
Evidence That Cooper’s Hawks Mate for Life
There is some evidence from field observations that Cooper’s hawks may form long-term pair bonds:
– Researchers have observed banded Cooper’s hawks returning to nest in the same territory with the same mate year after year. This suggests long-term pair bonding is common.
– Cooper’s hawks appear to have low rates of extra-pair copulations compared to other hawk species, indicating a high degree of mate fidelity within pairs.
– Both male and female Cooper’s hawks invest significantly in breeding efforts, from courtship displays to nest construction and provisioning young. This parental investment may reinforce the pair bond.
– Pairs must coordinate and cooperate closely when breeding. Familiarity between long-term partners likely improves breeding success compared to new, unfamiliar mates.
However, there are also factors that point against lifelong monogamy:
– There are no large studies definitively proving lifelong pairing in Cooper’s hawks. Observations have been limited to small geographic areas over relatively short time periods (2-5 years).
– Genetic analyses to look for cases of extra-pair paternity have not been conducted extensively on wild Cooper’s hawk populations. The true rates of infidelity are not yet known.
– As a short-lived species, most Cooper’s hawks may not survive long enough for lifelong pairing to be common. Average lifespan is less than two years.
Why Would Cooper’s Hawks Seek Lifelong Partners?
There are several evolutionary theories that could explain why Cooper’s hawks may benefit from having long-term mates:
– **Increased reproductive success** – Familiarity between long-term partners may improve coordination during breeding and increase fledgling success rates compared to unfamiliar new mates each season.
– **Resource/territory defense** – Cooper’s hawks defend breeding territories. Having the same mate return to the same territory each year may improve the chances of retaining prime resources.
– **Improved parental care** – Male Cooper’s hawks assist substantially with nesting duties and provisioning young. Pairing with an experienced mate optimizes biparental care.
– **Genetic compatibility benefits** – Choosing the same genetically compatible mate each season may confer immune health or other genetic benefits to offspring.
However, there are also reasons why Cooper’s hawks may opt for serial monogamy and dissolve partnerships after breeding:
– **Reduced inbreeding** – Seeking new mates periodically lessens the chances of inbreeding depression in offspring.
– **Chance of increased fitness** – Females may leave previous mates or engage in extra-pair copulations to obtain superior or more genetically compatible genes.
– **Limited lifespan** – As a short-lived species, most Cooper’s hawks die before lifelong monogamy can occur. Seasonal serial monogamy may be more evolutionarily beneficial overall.
Comparison to Related Hawk Species
Examining the mating habits of related hawk species can provide insight into the evolutionary factors that may influence Cooper’s hawks’ behaviors:
– **Sharp-shinned hawks** – Closest living relative of the Cooper’s hawk. Displays seasonal monogamy but high rates of infidelity in males. Suggests serial monogamy is ancestral mating pattern.
– **Northern goshawks** – Larger accipiter hawk. Displays seasonal monogamy, but will take new mates readily if previous years’ mate does not return. Some nest site reuse.
– **Harris’s hawks** – Unusual among raptors for exhibiting polygyny (one male mates with multiple females). Indicates mating system flexibility.
– **Red-tailed hawks** – Show high nesting site fidelity. Males return to breeding sites, then females choose among multiple potential mates. Serial monogamy.
Overall, related hawks seem to predominantly demonstrate serial monogamy and readiness to take new mates. This suggests Cooper’s hawks likely evolved from ancestors without strong lifelong pair bonds.
Conclusion
In conclusion, the available evidence suggests that while some Cooper’s hawk pairs may reform long-term bonds over successive breeding seasons, lifelong monogamy into old age is unlikely the norm for the species as a whole.
Given the limited lifespan of most individuals, serial monogamy across seasons appears to be the dominant mating system. However, monogamy within a given breeding season is common. More extensive long-term studies on wild Cooper’s hawk populations will be needed to better understand the prevalence of long-term pair bonding versus serial monogamy in this species.
Comparisons to related hawk species indicate that seasonal monogamy with relatively high mate fidelity, but ultimately serial monogamy, is the ancestral mating pattern for accipiter hawks like the Cooper’s. This makes lifelong monogamy unlikely to have evolved as a core reproductive strategy in Cooper’s hawks, though future research could reveal a stronger propensity for long-term pair bonding than is currently evident.
References
Rosenfield, R. N., Bielefeldt, J., Affeldt, J. L., & Beckmann, D. J. (2019). Breeding chronology, movements, and life history observations of Cooper’s Hawks in Wisconsin. Journal of Raptor Research, 53(2), 182-192. |
Curtis, O. E., Rosenfield, R. N., Bielefeldt, J., & Stewart, A. C. (2006). Cooper’s Hawk (Accipiter cooperii). In A. Poole (Ed.), The Birds of North America. Ithaca, NY: Cornell Lab of Ornithology. |
Estes, W. A., & Mannan, R. W. (2003). Feeding behavior of Cooper’s Hawks at urban and rural nests in southeastern Arizona. The Condor, 105(1), 107-116. |
Key Takeaways
- Cooper’s hawks form seasonal pair bonds and defend breeding territories.
- Some evidence indicates Cooper’s hawk pairs may stay together across multiple seasons, but this has not been definitively proven.
- Lifelong monogamy into old age is unlikely due to the short average Cooper’s hawk lifespan.
- Serial monogamy appears to be the dominant mating system as in related hawks.
- More extensive long-term studies on wild Cooper’s hawks are needed.