Blackbirds are a familiar sight, prompting curiosity about their mating habits. Understanding blackbird mating involves exploring avian pair bonds.
Understanding Avian Monogamy
The term “mating for life” in birds is intricate. In ornithology, a distinction exists between social monogamy and genetic monogamy. Social monogamy describes a pair of birds that live together, share a territory, and cooperate in raising their young. This arrangement is prevalent, with approximately 90% of bird species exhibiting social monogamy.
Genetic monogamy, in contrast, means that a pair exclusively reproduces with each other, with all offspring in a nest being genetically related to both parents. Despite the widespread nature of social monogamy, true genetic monogamy is quite rare in birds. Many socially monogamous species engage in extra-pair copulations (EPCs), where individuals mate with partners outside their primary social bond. This behavior can lead to offspring in a nest being sired by multiple males, introducing genetic diversity.
Blackbird Pair Bonds
Common blackbirds (Turdus merula) are primarily socially monogamous. They often form pair bonds that can last for a single breeding season or persist across multiple years. During the breeding season, both sexes are territorial, defending their chosen area from other blackbirds.
Male blackbirds engage in courtship displays to attract a female, which can involve oblique runs, head-bowing movements, and a low, “strangled” song. Once a pair forms, the female typically constructs a cup-shaped nest using twigs, leaves, and mud, often in shrubs or hedges. Both parents cooperate in raising their young, with the female incubating eggs and both feeding chicks after hatching. While maintaining a social bond, studies show common blackbirds can have extra-pair paternity, with up to 17% of offspring sired by a male other than the social mate.
Factors Affecting Pair Stability
Although blackbirds often maintain their pair bonds, several factors can influence the stability and duration of these partnerships. Breeding success is a significant factor. If a pair experiences an unsuccessful breeding season, they may “divorce” and seek new mates. Studies on common blackbirds have noted pair separation rates of up to 20% following poor breeding outcomes.
Territory quality also plays a role; if a territory is poor in resources or unsuitable for breeding, pairs may relocate. Age and experience contribute to bond stability, with older, more experienced pairs exhibiting greater stability. Mortality of one partner naturally dissolves the pair bond, prompting the surviving bird to find a new mate.