Birds reveal the evolutionary importance of love

Date: September 14, 2015

Source: PLOS

Summary: Humans are extremely choosy when it comes to mating, only settling down after a long screening process involving nervous flirtations, awkward dates, humiliating rejections and the occasional lucky strike. But evolution is an unforgiving force — isn’t this choosiness rather a costly waste of time and energy when we should just be ‘going forth and multiplying?’ What, if anything, is the evolutionary point of it all? A new study may have the answer.

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 tease apart the consequences of mate choice.

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.

Watching the couples’ courtship showed some noticeable differences — although non-chosen males paid the same amount of attention to their mates as the chosen ones did, the non-chosen females were far less receptive to their advances, and tended to copulate less often. An analysis of harmonious behavior revealed that non-chosen couples were generally significantly less lovey-dovey than the chosen ones. 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.

Overall 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 isn’t 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 couple’s likelihood of perpetuating their genes through their thriving offspring.

Sounds familiar? This is presumably what the human dating game is about, the need perhaps exacerbated by the extended phase of dependence during which our children need parental support. Indeed, these authors’ results are consistent with some studies on the differences between love-based and arranged marriages in human society.

Story Source:

The above post is reprinted from materials provided by PLOS. Note: Materials may be edited for content and length.

Journal Reference:

  1. Malika Ihle, Bart Kempenaers, Wolfgang Forstmeier. Fitness Benefits of Mate Choice for Compatibility in a Socially Monogamous Species. PLOS Biology, 2015; 13 (9): e1002248 DOI: 10.1371/journal.pbio.1002248

You Snooze, You Lose: Less Sleep Leads to More Offspring in Male Pectoral Sandpipers

ScienceDaily (Aug. 9, 2012) — During the breeding season, polygynous male pectoral sandpipers that sleep the least sire the most young. A team of researchers headed by Bart Kempenaers from the Max Planck Institute for Ornithology in Seewiesen has now discovered this extraordinary relationship. During three weeks of intense competition under the constant daylight of the Arctic summer, males actively court females and compete with other males.

Courtship flight: This male is trying to impress any watching female sandpipers with its feats of flight and inflated chest. (Credit: Wolfgang Forstmeier)


Using an innovative combination of tags that monitored movement, male-female interactions, and brain activity in conjunction with DNA paternity testing, the authors discovered that the most sleepless males were the most successful in producing young. As the first evidence for adaptive sleep loss, these results challenge the commonly held view that reduced performance is an evolutionarily inescapable outcome of sleep loss.

Sometimes it would be nice to have 24 hours available to finish the workload of the day. However, the drive for sleep inevitably compromises our performance or even causes us to fall asleep under dangerous situations, such as driving a car. Daily sleep is therefore thought to be essential for regenerating the brain and maintaining performance. This holds true both for humans and other animals. Researchers led by Bart Kempenaers from the Max Planck Institute for Ornithology in Seewiesen have now found that during the three-week mating period male pectoral sandpipers (Calidris melanotos) are active for up to 95% of the time. This is even more remarkable considering the fact that the birds have just arrived in their breeding area in Alaska, after migrating from their overwintering grounds in the southern hemisphere.

Pectoral sandpipers have a polygynous mating system where one male mates with several females. Because males do not engage in parental care, a male’s reproductive success is determined exclusively by his access to fertile females. However, gaining this access is not that easy for pectoral sandpipers: “Males have to constantly repel their rivals through male-male competition and simultaneously convince females with intensive courtship display,” says director Bart Kempenaers. Given that the sun never sets during the Arctic summer, males that can engage in this extreme competition 24/7 should be at an advantage.

Indeed, the researchers found that the most active males interacted most with females and sired the most offspring. Paternity was determined by collecting DNA from all males, all females, and all offspring in the study area. To measure activity patterns, the researchers attached transmitters to the feathers of all males and most of the females. These radiotelemetry based senders allowed the team to monitor whether the animal was moving or resting. Finally, recordings of brain and muscle activity confirmed that active birds were awake and that inactive birds were in fact sleeping.

The brain activity recordings also reveal variation in sleep intensity: “Males that slept the least had the deepest sleep,” says co-author Niels Rattenborg who conducts sleep research at Seewiesen. Although this suggests that the birds might compensate for sleep loss by sleeping deeper, the researchers found that even when this was taken into consideration, the birds were still experiencing a deficit in sleep.

Based on the team’s data on birds that returned to the study area across breeding seasons, this reproductive sleep loss apparently has no long-term adverse impact on survival. On the contrary, successful males returned to the breeding area more often when compared to males siring less offspring and were more likely to sire offspring in their second year. Does the study question the dominant view that the function of sleep is to regenerate the brain? The researchers do not wish to go that far, although the findings clearly show that under certain circumstances animals may be able to evolve the ability to forgo, or postpone, large amounts of sleep while maintaining high neurobehavioral performance.

Importantly, the finding that not every male does this, even when there are fertile females around, suggests that “Long sleeping males may lack genetic traits that enable short sleeping individuals to maintain high performance despite a lack of sleep,” argues Bart Kempenaers. The researchers believe that determining why only some males engage in this adaptive sleeplessness may provide insight into the evolution of this extreme behaviour, as well as the ongoing debate over the functions of sleep and its relationship to health and longevity in humans.

Story Source:

The above story is reprinted from materials provided byMax-Planck-Gesellschaft.

Journal Reference:

  1. John A. Lesku, Niels C. Rattenborg, Mihai Valcu, Alexei L. Vyssotski, Sylvia Kuhn, Franz Kuemmeth, Wolfgang Heidrich, and Bart Kempenaers. Adaptive Sleep Loss in Polygynous Pectoral SandpipersScience, 9 August 2012 DOI: 10.1126/science.1220939


Max-Planck-Gesellschaft (2012, August 9). You snooze, you lose: Less sleep leads to more offspring in male pectoral sandpipers.ScienceDaily. Retrieved August 11, 2012, from