When it comes to a song sparrow attracting a mate, the little feathered fellow may want forget about the singing audition and worry more about his smell, according to one Western PhD student.
Biologist Leanne Grieves has discovered that preen oil, long assumed to be used by birds for waterproofing and feather maintenance, may actually be saying more than we thought. Her findings not only offer insights into how birds attract mates, but also warn how human alterations to the environment may be masking matters.
“People used to think birds couldn’t smell or that smell was not at all important for them. But in the last 20 years or so, we have been looking more deeply at this,” Grieves said. “We usually think about birds singing to attract mates and using their plumage, too. From the human aspect, we see and hear these beautiful birds and we think that’s all they need.”
But she believes there is far more to consider.
Analyzing the preen oil, Grieves discovered it expressed different chemical makeups in males and females. Therefore, you could distinguish between genders simply by looking at the chemical composition – but that difference only appeared in breeding season. Once over, the change disappeared.
The discovery was interesting, but Grieves still wondered if the birds were actually using the oil to find a mate or was it simply a by-product of their metabolism or physiology. She’s began her testing by exploring the preen oil from different birds.
Grieves referenced a 1995 study from Swiss biologist Claus Wedekind – referred to as the ‘Sweaty T-Shirt Study.’ In the study, men wore the same shirt for two days. Women then smelled the shirt to determine which scent they were most sexually attracted to. Most women were attracted to those with an MHC – major histocompatibility complex – most dissimilar from theirs.
An important components of the immune system, MHC is a group of genes that code for proteins found on the surfaces of cells that help the immune system recognize foreign substances. MHC proteins are found in all higher vertebrates.
“If fish and mammals do it, you would think everything in between – the reptiles, the amphibians and the birds – also would do it,” she said. “When it comes to choosing a mate, the idea is that if this is such an important immune gene region – and we know it is – they will choose MHC dissimilar mates. But we didn’t know how they did this. We’re still just learning birds can actually do this.”
Using a Y-shaped maze, Grieves placed a song sparrow at the bottom and two cotton balls, one soaked with preen oil from an MHC dissimilar female and the other with MHC similar, at the top in two chambers. She found was the male spent more time with the MHC dissimilar smell.
“We think, for the health of their young, they are choosing a healthier mate,” she said. “Because that gene region is so important, there is gene-selection pressure for them to make good choices. Whether or not they know why they are making the choice, there is a drive to make that good choice.”
With quite a diverse gene region in the birds – with Grieves finding more than 300 different proteins – the birds could even be looking for a mate who is optimally different from them, because too many alleles can also lead to auto-immune diseases. They might be hyperreactive, sort of a Goldilocks scenario, she added.
“When it comes to wildlife, we already know noise impacts animals,” said Greives, adding her research could potentially assist other grassland species that are a priority for protection. “Pumping a lot of smells from industry, maybe animals will have a harder time smelling each other. If they’re ingesting pollutants, maybe it will change how they smell. That could affect things. We need to factor in when thinking about noise, other disturbances or what goes into our environment. It’s something for humans explore in the future.”