Key Factors Favoring Monogyny in Birds

1. Male Assistance in Offspring Rearing

One of the strongest evolutionary drivers for monogyny in birds is the requirement for both parents to successfully raise offspring. In many bird species, the demands of nest building, incubation, feeding, and protecting the young are so high that a single parent cannot manage alone. When male participation is crucial for chick survival, natural selection strongly favors monogynous pair bonds. This system ensures that both parents invest in the brood, maximizing reproductive success and offspring survival.

2. Mate Guarding

Another important factor is the need for males to guard their mates against rival males. In species where females may mate with multiple males if left unguarded, males benefit from staying with a single partner to ensure their own paternity. By remaining close and guarding the female, the male increases the likelihood that his genes are passed on, which reinforces the evolution of monogynous mating systems.

Why Sperm Limitation Is Not a Primary Driver

The idea that one male may not produce enough sperm to fertilize all the eggs produced by a female is not a significant evolutionary force for monogyny. In nearly all bird species, males produce sufficient sperm to fertilize the eggs of a single female, and often many more. Sperm limitation is extremely rare and does not typically shape mating system evolution in birds.

Scientific Consensus

Large-scale studies and evolutionary models confirm that monogyny in birds is most likely to evolve under conditions where male parental care is essential and/or mate guarding is necessary. These factors are repeatedly cited as the main ecological and behavioral pressures leading to strong, enduring pair bonds and cooperative breeding.

Conclusion

The situations most likely to lead to the evolution of monogyny in birds are:

• A. Male has to assist the female in rearing the offspring.

• B. Male guards the female against other males trying to mate with her.

Thus, the correct answer is:

(3) A and B