Mating systems are part of nature. Polygamy, which is one type of mating system, occurs infrequently with birds when compared to other mammals. Here's an overview of polygamy and how it relates to birds.
What Does Polygamous Mean?
(adjective) Polygamous describes the behavior of mating with several partners during a single breeding season, generally when one male mates with several females. The reverse (a female mating with several males) may be referred to as polyandrous behavior or polyandry instead of polygamy, though polygamy can apply to either gender. Many birds are polygamous to increase their chances of reproductive success and passing on their genes to the next generation of chicks.
(rhymes with chivalrous or "deliver us")
Why Birds Have Different Mates
There are many reasons why polygamy is beneficial to birds. When a bird has several mates, the genetic combination of traits for the resulting offspring is more varied. This increases the chances that at least some chicks will be stronger, faster, smarter, and better equipped to survive to maturity. Other reasons for polygamy include:
- Increasing individual brood size by using multiple mates, which creates a larger next generation in case of higher mortality rates. When more eggs are laid, it is likely that more chicks are able to survive.
- Connecting to multiple mates that can provide support while eggs are being incubated or very young chicks need extra care and protection. More adult protectors can safeguard young chicks better.
- Raising multiple broods each breeding season. Different mates may provide care for younger broods even while more eggs are laid and hatched.
All of these reasons help increase the chances of each adult, mating bird being able to pass their genes on to a new generation of chicks.
Polygamous Bird Relationships
Polygamous behavior is quite widespread among birds but the degree of polygamy can vary greatly. It is much more common for males to have multiple female partners during the nesting season. In some species, however, females are known to have multiple male partners, even to the point of raising broods in which siblings have different fathers. Polygamy is most common in harsh nesting conditions that make it necessary for birds to use several partners to increase the chances of surviving offspring.
In a polygamous mating, the less polygamous partner, typically the female, is responsible for the majority of the care and raising of the young, from nest building to incubation to feeding. Duties may be shared, however, depending on the partner’s level of polygamy and the condition of additional mates. In some cases, adults of the same gender may not compete, but rather cooperate with co-mates to ensure all the chicks have better care and a greater chance of survival.
Why Bird Polygamy Doesn't Always Work
While polygamy may have negative associations with human relationships, it is important to remember that birds do not have the same lifelong connections to their mates. Even many bird species that typically mate for life can be polygamous under the right conditions. The most important thing is for chicks to survive and thrive, no matter how many mates are necessary. Polygamy doesn't work for all bird species, however, and some birds, including many raptors, cranes and other long-lived species, are almost exclusively monogamous. Polygamy will not work when birds require:
- Very lengthy, labor-intensive courtship rituals. When birds have to use elaborate courtship displays to impress a prospective mate, it may take too long to find multiple mates suitable for breeding. In this case, it makes more sense to stay with one monogamous mate and concentrate efforts on raising chicks with the best possible partner.
- Long nesting or chick care periods. When young chicks may rely on their parents' care for several weeks or months before they can be independent and leave the nest, polygamous relationships will not work. Mated birds will not have enough time to raise several broods during the year, and instead will need to focus on just one partner and their offspring.
- Very lengthy migrations and extremely short nesting periods. Birds that have very distant breeding and wintering ranges may not have time to court and mate with several partners during a short breeding season. Instead, remaining loyal to a single, strong partner can be the best strategy for successful reproduction.
These are not hard and fast rules, and with 10,000 bird species in the world, there are many different ways polygamy can work for some species but not for others.
Polygamous Bird Species
The majority of the world's bird species can be considered polygamous to some degree, depending on how avian polygamy is classified. In general, birds are not declared to be absolutely polygamous unless it is well-documented that most members of the species deliberately and consistently seek out several different mates during the same breeding season. If polygamy occurs only rarely or just under exceptional conditions, the species may not be considered truly polygamous. For rare, endangered, or less-well-studied species, the overall mating habits are not often known and it can be difficult to judge whether those avian relationships are polygamous or not.
Also Known As
Polyandry, Polyandrous (one female mating with several males)