Birds exhibit a variety of mating systems, ranging from monogamy (one male pairing with one female) to polygyny (one male pairing with multiple females) to polyandry (one female pairing with multiple males). The type of mating system a bird species exhibits depends on various ecological, biological and behavioral factors. Understanding the differences between monogamous and polygamous birds provides insights into avian evolution, reproduction, behavior and conservation.
Definitions
Monogamy refers to a mating system where one male forms a long-term pair bond with one female. The male and female cooperate in raising young. Around 90% of bird species are socially monogamous, including albatrosses, swans, geese, eagles, penguins and owls. However, genetic monogamy, where both parents contribute equally to the gene pool of offspring, is rare. In many socially monogamous species, females will copulate outside the pair bond.
Polygyny refers to one male mating with multiple females. The male does not provide parental care and defends a territory or resources to attract mates. Polygyny is common in species where males can monopolize resources, like lekking grouse, pheasants and birds of paradise.
Polyandry is when one female mates with multiple males. This is rarer than polygyny in birds. Examples include phalaropes, jacanas and dunnocks. Often, the males provide all parental care in polyandrous species.
Factors Influencing Mating Systems
Several ecological and biological factors influence the mating system of different bird species:
- Parental care – Monogamy is linked to biparental care of offspring. Polygamy occurs when male parental care is absent.
- Habitat and resources – Polygyny happens when males can control resources to attract multiple mates, like defending prime nesting or feeding territories.
- Sex ratio – Polyandry arises when there is a female-biased sex ratio and intense competition between males for access to mates.
- Sexual dimorphism – Larger size differences between males and females promote polygyny.
- Life history – Shorter lived species with multiple breeding attempts per season tend towards polygamy.
Behavioral Differences
The mating system shapes the behavior of monogamous versus polygamous birds:
Pair Bonding
Monogamous birds form long-term pair bonds. Partners coordinate nest building, incubating eggs, provisioning young and defending territories together. Polygamous males put effort into mate acquisition rather than pair bonding.
Courtship and Mating
Monogamous males court and mate with their pair bonded female. Polygamous males have elaborate courtship displays to attract multiple mates for brief copulations. Lekking species like grouse gather at communal display grounds where females pick mates.
Parental Care
Both parents care for offspring in monogamous species. Polygamous males provide little or no care. Females get help raising young from earlier nests or nest in loose colonies for communal defense in polygynous species. Polyandrous females dump the eggs with their mates for male-only care.
Aggression
Monogamous pairs may defend shared resources. Polygamous males are often highly aggressive fighting off rival males. Polyandrous female aggression can help control male behavior.
Examples of Polygamous Bird Species
Here are some examples of polygynous and polyandrous birds:
Polygynous Species
- Pheasants and peafowl: Males maintain harems of females. Display trait size signals mate quality.
- Lekking grouse and manakins: Males gather at communal arenas to display and mate with visiting females.
- Birds of paradise: Males defend mating territories using elaborate plumage.
- Red-winged blackbirds: Males control optimal marsh nesting habitat to attract up to 15 females.
- Great reed warblers: Females nest in dense territories of males who provide no care.
Polyandrous Species
- Phalaropes: Females are larger and more colorful. Males incubate eggs and care for chicks.
- Spotted sandpipers: Females nest with several males who provide paternal care.
- Dunnocks: Females aggressively fight other females and mate with multiple males who help at nest.
- Galapagos hawks: Territories contain multiple breeding males.
- Jacanas: Females defend territories while males incubate eggs and raise chicks.
Reproductive Success
Mating system differences impact reproductive success:
Monogamous Birds
– Biparental care improves offspring survival
– Long-term pair bond enhances coordination and breeding success
– Lower male mating opportunities balanced by paternal care
Polygamous Birds
– Male mating skew – dominant males sire more offspring
– Little or no paternal care can decrease survival
– Female choice and competition for quality mates
– Increased risk of sexually transmitted diseases
Evolutionary Theories
Several ideas explain evolution of avian mating systems:
- Polygamy threshold model – Polygamy emerges when male parental care does not improve reproductive success.
- Female preference model – Polygamy arises when females prefer mating with already mated high quality males.
- Constraint model – Monogamy results from ecological constraints that preclude polygamous systems.
- Life history model – Polygamy correlates with low adult survival, multiple brooding and rapid maturation.
No single model explains all situations. Evolution of mating systems depends on complex ecological and sexual selection pressures.
Conclusion
In summary, monogamous bird species form long-term pair bonds characterized by biparental care of offspring. Polygamous species exhibit one of three systems – polygyny, polyandry or promiscuity based on whether males, females or both sexes mate with multiple partners respectively. Factors like sex ratios, sexual dimorphism, habitat and life histories shape the evolution of mating systems. Polygamy arises when one sex can monopolize access to mates by controlling resources. Monogamy emerges with biparental care, constraints and slow life histories. Mating patterns influence behavior, reproduction and conservation issues in birds. Polygamous species often exhibit dramatic breeding displays. However, monogamous family living may confer advantages for stability and offspring survival over mating system alternatives. Understanding avian mating systems provides fascinating insight into sexual selection and life history theory.