Female birds cheat on partners to mate with smarter males

Gambel's Chickadee. Photo: Wikimedia Commons

Scientists have long paid attention to the Gambel's Chickadee (Poecile gambeli) — a species from the tit family that inhabits the mountainous regions of western North America from southern Yukon to California and Texas. These birds do not undertake long seasonal migrations, form long-term pairs, and occupy the same territory year after year, enduring harsh mountain winters together.

The survival of Gambel's Chickadees largely depends on spatial memory. Every autumn, they hide seeds throughout their territory, and in winter, when there is almost no other food, they must find these caches — up to 1000 of them! — under the snow.

Previous studies have shown that Gambel's Chickadees exhibit individual differences in spatial memory. Birds that most efficiently find their food caches more often survive their first winter and live longer on average.

Moreover, this ability is partially inherited and linked to genes that influence the development of the hippocampus — the part of the brain responsible for spatial memory. Such results prompted researchers to a new question. If good memory is so important for survival and passed on to offspring, can it also affect reproductive success?

To answer this question, as Earth.com writes, researchers observed a wild population of Gambel's Chickadees in northern California for several years. First, they needed to assess each bird's spatial memory.

To do this, scientists used a system of "smart" feeders hung in the forest. Each feeder read the bird's electronic tag, but only one of several feeders was assigned to a specific individual and dispensed a reward — a sunflower seed.

To get food, the bird had to remember which feeder was intended for it. The more incorrect feeders it visited before finding the correct one, the worse its results were considered.

Over four days of testing, some chickadees quickly memorized the correct location and made few mistakes. Others continued to visit incorrect feeders repeatedly. This way, researchers obtained an objective assessment of each bird's memory.

Павялічыць

Gambel's Chickadee. Photo: Wikimedia Commons

Infidelities happen more often than expected

Along with memory tests, researchers conducted genetic paternity analysis over three breeding seasons. They compared the true father of each chick with the social male who raised it.

The results were unexpected. About a third of all chicks studied — 222 out of 732 — were not fathered by the male who cared for the nest. Approximately 70% of nests contained at least one chick from a different father.

Sharpness of mind helps win additional mates

It turned out that such cases were not random. The fathers of extra-pair offspring were most often males who showed the best results in memory tests. The most capable "students" could leave six to seven additional chicks per season, while males with the worst results left only one or two.

Moreover, the rather common pattern in the animal world, where older and more experienced males are favored, did not apply. In Gambel's Chickadees, reproductive success was determined not by age, but by the ability to navigate well in space.

Loss of paternity costs nothing

One might expect that a male seeking extra-pair liaisons would neglect his own nest. However, the data revealed no such losses.

Males who fathered other chicks raised as many young in their own nests as those who had no extra-pair success. There was no difference between the two groups in brood size or chick weight.

Furthermore, males with better spatial memory on average raised heavier chicks, and a greater body mass at an early age increases chances of survival.

Smarter lover wins

The main conclusion of the study was that if extra-pair chicks were found in the nest, their true father almost always demonstrated better spatial memory than the female's social partner.

At the same time, the likelihood of losing part of paternity did not depend on the male's own memory at all. Another circumstance turned out to be much more important: females who performed worse on memory tests were more likely to have extra-pair offspring.

Researchers suggest that such females may seek smarter partners to compensate for their own cognitive shortcomings and pass on more beneficial inherited traits to their offspring. Since genes related to spatial memory are not sex-linked, they can be inherited by both sons and daughters, a female with poor memory can give her offspring a real advantage by mating with a smarter male.

The study authors believe they have obtained one of the most convincing pieces of evidence that sexual selection can directly influence the development of intellectual abilities in the wild. While it was previously known that good memory helps chickadees survive, it is now clear: it also helps them leave more offspring.

In other words, evolution rewards intelligent birds twice — first with the opportunity to survive winter, and then with greater chances to pass their genes to the next generation.

• 24
• 1
• 3
• 1
• 5
• 2
• 0
• 0