The coat makes up the bravery of male swallows

A new study conducted by the University of Colorado at Boulder showed that sex hormones in male North American swallows skyrocketed during the breeding season when researchers darkened their breast hair color. . This suggests that the color of the coat makes up the nature of the male.

Professor Rebecca Safran, the lead author of the study, said that when the crimson chest hair of male swallows is considered the sexiest for females. Their level of sexual hormones increases due to their ' emotional exchange ' with their children as well as the battles that occur with jealous males. The sudden increase in genital hormones is unexpected because often in the reproductive cycle, the level of sexual steroids such as reduced sex hormones.

Safran said: 'This is a big surprise when only a small change of appearance has a significant physiological impact on male swallow birds . Experimental manipulation not only improves their appearance in the eyes of females, but also changes their chemical system. The relationship between the physiological characteristics of males and the characteristics that help it gain more flexibility than we think. '

A research paper published in Current Biology on June 3. Co-author of the study includes James Adelman and Michaela Hau of Princeton University; Kevin McGraw of Arizona State University. This two-year study is funded by the National Science Foundation.

This is the first study to show a significant relationship between appearance and physiological function in birds, and the study provides more specific ecological and evolutionary insights. Physiological signs such as coat color.

Professor Rebecca Safran of the University of Colorado Department of Ecology and Biological Ecology at Boulder removed a North American swallow from the net, marked it and released it.(Photo by Kevin Stearns)

She said: 'Due to the current evolutionary characteristics of the swallow, it is the talent of raising children, so from this research we get the message that the male is dark, at least for the North American barn, yes more advantageous than light-colored ones. The fact that darker males have higher levels of sex hormones may be the reason why they are more successful. '

Safran's studies show that male swallows from North America, Europe and the Middle East have different looks, thereby providing clues about the influence of female choices on the new species formation process. For European barn swallows, long tail feathers, not crimson breasts, are a foreshadowing of fertility success.

Saran explains: 'Swallows studies in the Middle East, Europe and North America give us a glimpse into the evolutionary process including the formation of new species. Females play a decisive role, they create differences that can be observed in male swallows around the world, from breast hair color to tail feathers' shape.

North American barn swallows use breast hair color in exchange for status, health and the ability to successfully raise children . A 2005 study by Safran and colleagues published in Science showed that male swallows with darker breast hairs gave birth sooner and had more children. Children choose them to be 'adultery' with other males less. She said: 'These results provide clear evidence that coat color is an important quality indicator for males.'

Sexual signals of males in the animal world, from the majestic antlers of the deer to the elaborate tail feathers of the peacocks, have evolved in exchange for 'accurate and truthful information'. Evolutionary biologists believe that the dominant males in the herd may suffer some physiological damage through exaggerated sexual expression. The dark coat of attention both causes biochemical damage and makes them vulnerable to predators.

Safran said: 'The male swallow bird cannot look in the mirror and evaluate its status in the herd. But if it flies in a group with other swallows, they will quickly assess it to help it realize its status. Because of the status regarding the pack that it lives with, it might be 'the same in this herd but just a normal guy in another flock.' '

She compared this biochemical feedback mechanism to a man who had just left a row of clothes and a new set of clothes. She said: 'When he says he feels worth millions of dollars, that could be the effect of biochemical feedback. This result is similar to when we have the opportunity to improve our status, for example, to obtain a prestigious award or to be invited to a special event '.

Kevin McGraw, of the ASU School of Life Sciences, co-author of the study, said: 'The traditional view for birds is the internal transformation process that defines external characteristics - or in other words, function. physiological ability to create the fur . But the results we have shown indicate that changing the coat color in animals can directly affect its physiological state. The amount of hormone in a swallow is affected by its appearance. '

In the new Current Biology study , the scientists captured 63 male barn swallows from six areas in New Jersey at the start of the breeding season when the birds arrived at the breeding site and began to mate. About half of them are colored in breasts for the darkest and sexiest fur in their flock.

The marked birds were released back into the wild, then captured again a week later. They are given a blood test to check hormone levels, including sex hormones. In addition to increasing levels of hormones, marked birds also lose weight, probably because they are more active than light-colored ones, or they simply cannot reach expectations from other swallows because Their ' fake ' sex signs.

Mitochondrial DNA cluster analysis in swallows shows that the European swallows and North American swallows are more likely to be separated from the same ancestral species that resided in Africa several million years ago. Safran's research helps other researchers gain a deeper understanding of the process of rapidly evolving traits common to birds when choosing partners.