Birds who freely choose their own mates have 37 percent more offspring as compared to birds that are paired up
Birds who freely choose their own mates have 37 percent more offspring as compared to birds that are paired up. The findings have a far-reaching implication for conservation and captive breeding practices.
The authors conclude that birds vary rather idiosyncratically in their tastes, and choose mates on the basis that they find them stimulating in some way that isnt necessarily obvious to an outside observer. This stimulation turns on the females to increase the likelihood of successful copulation and encourages paternal commitment for the time needed to raise young; together these maximize the couples likelihood of perpetuating their genes through their thriving offspring.
Doing a cost/benefit analysis of love is a challenging business, with many potential confounds, and in the case of humans some ethical limitations on doing experiments. A new study publishing on September 14th in the Open Access journal PLOS Biology by Malika Ihle, Bart Kempenaers, and Wolfgang Forstmeier from the Max Planck Institute for Ornithology, Seewiesen, Germany, describes an elegant experiment designed to see the consequences of mate choice.
In this study, the authors tested the parental compatibility hypothesis by keeping mate quality constant as they untangled the direct and indirect benefits of partner compatibility. Mate choice for behavioural compatibility would be most important in species that form long-lasting monogamous pair bonds where both parents care for their offspring.
The authors took advantage of the fact that the zebra finch shares many characteristics with humans, mating monogamously for life, and sharing the burden of parental care. Female finches choose mates in a way that is specific to the individual, and there is little consensus among females as to who the cutest male is.
Using a population of 160 birds, the authors set up a speed-dating session, leaving groups of 20 females to choose freely between 20 males. Once the birds had paired off, half of the couples were allowed to go off into a life of wedded bliss. For the other half, however, the authors intervened like overbearing Victorian parents, splitting up the happy pair, and forcibly pairing them with other broken-hearted individuals.
Bird couples, whether happy or somewhat disgruntled, were then left to breed in aviaries, and the authors assessed couples behavior and the number and paternity of dead embryos, dead chicks and surviving offspring.
Strikingly, the final number of surviving chicks was 37% higher for individuals in chosen pairs than those in non-chosen pairs. The nests of non-chosen pairs had almost three times as many unfertilized eggs as the chosen ones, a greater number of eggs were either buried or lost, and markedly more chicks died after hatching. Most deaths occurred within the chicks first 48 hours, a critical period for parental care during which non-chosen fathers were markedly less diligent in their nest-care duties.
There was also a higher level of infidelity in birds from non-chosen pairs interestingly the straying of male birds increased as time went by while females roamed less.
Dr Ihle and her colleagues discovered other behavioural effects as well. Although males from both treatment groups courted their partner equally often, they found that females were significantly less responsive to their partner during courtship if they were in an arranged marriage. Additionally, the researchers found that within-pair responsiveness was not affected by pair bond duration. In non-chosen pairs, 16 percent of courtships led to copulation, which was only slightly lower than the rate of 20 percent in chosen pairs.