Sandhill cranes are large birds that mate for life. However, while sandhill crane pairs typically stay together until one mate dies, they do occasionally “divorce” and find new mates. In this article, we’ll explore whether sandhill cranes actually get divorced and the reasons why crane pairs may split up.
Do sandhill cranes mate for life?
Sandhill cranes form long-term pair bonds that can last for years or even decades. Most pairs remain together until one of the cranes dies. However, sandhill cranes are serially monogamous rather than purely monogamous. This means that while they mate for life in any given breeding season, if one mate dies, the surviving crane will find a new mate the next season. The long-term pair bond dissolves with the death of one of the mates.
Pairs establish their bond through elaborate “unison calls” and dances that sync their movements. Using their calls, they are able to stay in constant communication even when out of sight of each other. Cranes mate for life to increase reproductive success. By working together, pairs can better defend their nesting territory, build nests, incubate eggs, and raise young. Cranes that have a consistent mate from year to year have higher hatching and fledging success than unpaired birds.
Do sandhill cranes ever divorce?
While sandhill crane pairs mostly stay together until death, some pairs do occasionally split up in a form of “divorce.” This usually happens after a failed breeding season when no chicks are produced. The failure to breed successfully puts stress on the pair bond and can cause the birds to go their separate ways. However, cranes getting divorced is relatively uncommon. Estimates indicate around 2% of pairs in stable populations get divorced each year.
Even cranes that have been paired together for many years and raised multiple chicks may still occasionally divorce. One 15-year field study of sandhill cranes in Wisconsin found that 7% of established pairs with offspring ended up separating.
Reasons that crane divorce may occur include:
– Infertility issues in one of the birds
– The death or loss of multiple chicks over several breeding seasons
– Disagreements over parenting techniques or nesting sites
– External stresses like severe weather, lack of resources, or human disturbance
Why do sandhill crane divorces happen?
There are several theories as to why an established crane pair might make the rare decision to split up and find new mates.
**Infertility:** One of the mates may be infertile and unable to reproduce successfully after multiple failed breeding attempts. Rather than stay in a pair bond that cannot produce offspring, the fertile bird may leave to increase its chances of passing on genes.
**Personality clashes:** Like human couples, crane pairs may occasionally be incompatible in their personalities or temperaments. Conflicts over nesting sites, parenting duties, or other factors could build up over time and lead to divorce.
**Better mating prospects:** A crane may abandon its mate if a healthier, stronger, or more genetically fit single crane becomes available nearby as a potential new partner. Desire to mate with a more optimal partner can cause divorce.
**Loss of chicks:** The death of multiple chicks over several breeding seasons, either due to predators, disease, or harsh weather, puts severe stress on the pair. This could cause the birds to split up and try their luck with new mates.
**Nesting site issues:** Problems with the nesting territory, like threats from predators or loss of food resources nearby, could motivate a crane pair to divorce and search for better nesting sites elsewhere.
Reasons for sandhill crane divorce:
| Reason | Explanation |
|---|---|
| Infertility | One mate is infertile so the pair can’t reproduce successfully |
| Personality clashes | Incompatible temperaments and disagreements over nesting duties |
| Better mating prospects | Chance to mate with a healthier, fitter, or more genetically optimal new partner |
| Loss of chicks | Stress and grief over failed breeding attempts and death of chicks |
| Nesting site issues | Lack of food or threats from predators at the nesting site |
How do sandhill cranes find new mates after divorce?
When a sandhill crane gets “divorced,” meaning its established mate either dies or the pair bond dissolves, it must find a new partner before the next breeding season. Cranes begin this process as soon as they are unmated.
To attract potential new mates, divorced cranes will return to large breeding grounds where many other single cranes congregate. Likely spots include marshes, wetlands, and river basins where large flocks gather. The crane will join in group dances, displaying its fitness. Strong, healthy cranes are preferred mates.
Vocalizations also play a key role. Divorced cranes will call loudly and frequently to grab attention from unpaired cranes of the opposite sex. In addition to showing off with dances and calls, cranes may interact directly with potential new partners. They will preen each other’s feathers and synchronize their movements to form temporary pair bonds. This bonding behavior helps establish if they are compatible mates.
Most cranes successfully find new mates each season through these courtship rituals on breeding grounds. However, some older divorced cranes fail to attract a new partner and never breed again. After a few failed mating seasons, they may leave the breeding grounds and spend the rest of their years alone.
How long does it take sandhill cranes to find a new mate?
Sandhill cranes that get divorced during the breeding season must act quickly to find a replacement mate. They usually only have a few months between the dissolution of their old pair bond and the next breeding season. Cranes put substantial effort into displaying, bonding, and competing for the attention of new partners.
Most cranes successfully find new mates within one to three months after divorce or being widowed. The courtship and mating process happens rapidly so they can begin nesting as soon as possible. Some factors that influence how quickly a crane can attract a new mate include:
– **Age:** Younger mature cranes typically find new mates faster than older divorced cranes.
– **Health:** Cranes in robust health and good physical condition are more attractive to potential partners. Sick or injured cranes may struggle.
– **Gender:** Female cranes often have an easier time finding new mates than males on the breeding grounds.
– **Timing:** Cranes divorced earlier in the breeding season have more time to establish a new pair bond before nesting.
– **Location:** Cranes in areas with higher densities of unmated birds will pair up more quickly.
While most cranes successfully find new mates rapidly, those that fail to do so by the start of the breeding season will likely skip nesting that year. Older divorced cranes are the most likely to remain single for multiple seasons.
Do male and female sandhill cranes divorce at different rates?
Studies show that male and female sandhill cranes have about equal rates of divorcing their mates. Neither sex appears significantly more likely to abandon its partner and seek a new match.
However, there are some subtle differences between sexes in crane divorce patterns:
– **Females** may be slightly more likely to divorce an infertile mate. As the sex responsible for incubating eggs and raising chicks, females invest more in reproduction. An infertile male partner threatens their breeding success.
– **Males** may divorce at higher rates after the loss of multiple chicks. Males provide protection and defense for the nest, so continual nest failures may drive them to find new mates.
– Older **females** are somewhat more likely to successfully find new mates after divorce compared to older males. This may be because female fertility declines more slowly with age compared to males.
– **Males** are more likely to divorce a mate that has consistently chosen poor nesting sites, putting eggs and chicks at risk. Nests are the male’s territory to defend.
Overall though, both male and female sandhill cranes exhibit flexible mating strategies and appear to divorce previous mates at roughly equal rates when circumstances threaten their breeding productivity. Neither sex commitments absolutely for life to a single partner.
Sandhill crane divorce by sex:
| Sex | Divorce patterns |
|---|---|
| Female | May divorce infertile mates at higher rates |
| Male | May divorce after loss of chicks more often |
| Female | Older females find new mates more easily |
| Male | Males abandon mates that choose bad nest sites |
Do divorce rates vary across sandhill crane populations?
Divorce rates in sandhill cranes can vary across different populations and subspecies. Crane populations face different conditions depending on their geographic locations. Environmental factors like food availability, nesting habitat quality, population density, predator pressures, and human disturbances can all influence divorce rates.
Some key regional differences include:
– **Greater sandhills** in the Midwest U.S. have relatively low divorce rates around 2%. Their breeding grounds have plentiful resources.
– Sandhills in the **Rocky Mountains** divorce more frequently, upwards of 5% of pairs. This may be from lower habitat quality and greater predation.
– **Florida sandhills** have divorce rates under 3%. Their stable wetland habitats and mild climate support strong pair bonding.
– Migratory sandhills that breed in the **far northern U.S. and Canada** divorce more often, perhaps due to shorter breeding seasons and harsher conditions.
– Endangered **Mississippi sandhills** face very high nest failures, likely increasing divorce rates. Their limited genetics may also play a role.
– Sandhills in areas with more **human disturbance**, like farming and development, tend to have higher divorce rates.
The ability of crane pairs to successfully reproduce over many years seems to be the primary driver of divorce rates across varying habitats and populations. External stresses make divorce and re-mating more likely.
Sandhill crane divorce rates by region:
| Region | Estimated divorce rate |
|---|---|
| Midwest U.S. | 2% |
| Rocky Mountains | 5% |
| Florida | Under 3% |
| Northern U.S. & Canada | Over 5% |
| Mississippi | Potentially very high |
| Areas with more human disturbance | Over 5% |
How does divorce impact sandhill crane breeding and behavior?
Divorce among sandhill crane pairs, while not extremely common, can have significant impacts on their breeding patterns and behavior:
– Cranes that divorce and re-mate have **lower annual reproductive success** on average. Failed nests are more likely when new pairs are still bonding.
– Divorced cranes often must find completely new nesting territories after splitting up, which is energetically costly.
– Competition for mates is greater for older divorced cranes, forcing them to invest more time and effort into elaborate courtship displays.
– Cranes may be more aggressive as they establish new pair bonds and defend nesting sites. More conflicts with other cranes may erupt.
– Divorce and re-mating shuffles crane populations and can limit localized genetic diversity over time.
– Cranes raising chicks alone after divorce may provide lower quality parental care until they find new mates.
– If both adults are new immigrants to an area, they lack local experience and struggle to nest successfully.
Overall, sandhill crane divorce is an adaptive response to reproduction failure. But it comes with costs and risks that lower breeding potential compared to intact lifelong pairings. The impacts are most severe for older divorced cranes. Conservation efforts seek to provide optimal breeding habitats with low divorce rates.
Conclusion
Sandhill cranes have a reputation for being strictly monogamous birds that mate for life. In reality, while most crane pairs demonstrate extraordinary fidelity and remain bonded until the death of one mate, a small percentage do get “crane divorced” each year after failed breeding attempts. Divorce allows the birds to find new partners and continue breeding.
Rates of divorce vary between 2-7% across different crane populations and subspecies. Reasons for splitting up include infertility, personality conflicts, death of chicks, and disagreements over nesting territories. Cranes that divorce must rapidly find new mates each breeding season. This threatens their reproductive success and breeding behaviors. But divorce gives cranes that would otherwise breed unsuccessfully a chance to pass on their genes with a better suited partner. Though rare, divorce is an important element of the complex long-term mating strategies of sandhill cranes.
