How certain tree smells boost male bird testosterone levels

Greg Howard
11th February, 2024

Image Source: Natural Science News, 2024

When trees are nibbled on by insects, they release special chemicals into the air known as Herbivore-Induced Plant Volatiles (HIPVs). These chemicals serve as a SOS signal, and interestingly enough, the songs of birds perched on branches aren't the only things responding to these distress calls. Research has found that birds, particularly songbirds, can sniff out these airborne clues, which then guides them to their insect meals. However, scientists have now started to wonder: could these plant aromas also influence the birds' decisions about when to start a family? In a recent study, researchers decided to put a songbird species, the great tit (Parus major), under the microscope. During the period before breeding, these birds were given a whiff of the odors from trees that caterpillars had been feasting on. Scientists tracked what would happen next—specifically, they looked at when the great tits laid their eggs, how many eggs they produced, and how big these eggs were. The hormones driving reproduction, testosterone in males, and 17β-estradiol in females were also observed. The outcome? Females that were surrounded by the HIPVs didn't make any changes to their egg-laying schedules. They stuck to their usual timetable, laid the same number of eggs, and those eggs weren't any larger or different from those of female great tits that hadn't been introduced to the unique scents. Even the levels of 17β-estradiol, the hormone associated with egg development, remained steady across the board. But here's where it gets interesting. The male great tits told a different story. The males that had been exposed to the HIPVs had more testosterone during the egg-laying period than those who hadn't gotten a whiff of the plant emissions. This means that even though the female birds seemed to be unmoved by the scent of an impending insect buffet, the males were gearing up, potentially readying themselves for the responsibilities of fatherhood. What this study fundamentally underlines is the songbirds' remarkable ability to detect even tiny amounts of odor from plants. While the HIPVs didn't seduce the females into investing more in their reproductive efforts, the males appeared to be influenced by this additional piece of information when it came to seasonal breeding. In sum, the researchers have shone a light on the complex relationship between plants, insects, and birds, where a simple whiff of insect-induced stress in trees might be enough to kickstart a male songbird's testosterone-driven reproductive stride. However, the females appear to need more convincing than just the aromatic promise of a caterpillar feast to adjust their breeding plans.

Wildlife Ecology Animal Science

References

Main Study

1) Odours of caterpillar-infested trees increase testosterone concentrations in male great tits.

Published 9th February, 2024

https://doi.org/10.1016/j.yhbeh.2024.105491

References

Main Study

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