Question

What is the physiological reason (something about their internal biology) for why birds are more likely to pair-bond than mammals?

Answer 1

Pair bonds means strong affinity between a mating pair which lead to production and rearing of offspring for life time. There are some reasons why pair bonds are more strong in birds than mammals. In birds, life span is very short in comparison to mammals. So birds, once pairs, do not waste time to find out another mate which is the wastage of time. Instead of that birds prefer monogamy where they pair with a specific partner and leads their life with partner throughout. Birds are mostly monogamous whereas mammals are mostly polygamous. Another point is that, the interval between mating and egg laying is short in birds than mammals. So males in birds became more sure about their paternity of the offspring and thus provide more parental care to their own offspring.