Sandhill Cranes are recognized for their enduring pair bonds, often described as perennial monogamy. These large, migratory birds typically select a mate between the ages of two and seven, forming a relationship that persists through breeding and non-breeding seasons for many years. This strong bond is rooted in the necessity of bi-parental care, as both partners are required to successfully raise their young, known as colts. When one member of the pair is lost, it profoundly disrupts the surviving crane’s social structure and its ability to function successfully.
Immediate Behavioral Response to Loss
The immediate aftermath of a mate’s death involves observable behavioral changes in the surviving Sandhill Crane. The solitary crane often exhibits heightened arousal and unusual displays, sometimes spending a period searching the immediate area for its partner.
This searching behavior is accompanied by a significant increase in vocalizations, specifically loud, searching calls. These calls are distinct from the synchronized “unison calls” the pair would have performed. The crane may also temporarily isolate itself from other groups, exhibiting social withdrawal near the location where the mate was last seen. These intense, short-term reactions typically last for days or weeks before the survivor begins to integrate back into a solitary existence or a flock setting.
Survival Implications for the Solitary Crane
The loss of a mate creates significant practical challenges that compromise the crane’s long-term survival. The pair bond is a functional necessity, providing mutual defense and enhancing foraging success. A single crane is more vulnerable to predation, as one bird can no longer stand guard while the other rests or feeds.
Paired cranes are also more efficient at locating food resources; two sets of eyes are more effective at detecting threats and finding suitable foraging grounds. For a breeding pair, the loss of a partner can lead to the appropriation of their territory by neighboring pairs, especially if the survivor is female. Studies suggest that consequences are often more significant for females, who may struggle to defend a territory alone against established pairs. The inability to defend a territory and the reduction in vigilance increase the survivor’s daily energy expenditure and overall risk.
The Process of Re-Pairing
Despite the challenges, re-pairing is a common and biologically necessary outcome for the solitary crane. Since successful reproduction requires two parents, the survivor must eventually find a new partner to continue breeding. This process is rarely immediate and can take a considerable amount of time, sometimes months or even years, especially for non-migratory subspecies.
The surviving crane typically joins a non-breeding flock, often referred to as a bachelor group, consisting of sub-adults and other unattached individuals. Associating with these groups increases the crane’s opportunities to encounter a potential new mate. The re-pairing process involves renewed courtship rituals, including the famous Sandhill Crane “dancing,” which helps establish and synchronize the new bond. Successfully reproducing with a new partner is a major factor in perpetuating the pair bond, as pairs that fail to fledge young are more likely to separate.