Scientists say male shrikes eat impaled prey to improve singing
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The reputation of the male bull-headed shrike just took a dive.
Once seen as paragons of being practical for hoarding prey they’ve killed for the winter, it turns out the birds eat almost all of the cache before January.
Researchers have discovered they’re doing it as part of their effort to attract females.
“It turns out that male shrikes’ practice of impaling prey on thorns is important for them to court their lovers in a more attractive fashion,” said Yusuke Nishida, a specially appointed lecturer at Osaka City University who studies behavioral ecology. “They seemingly can’t exhibit courtship behavior well when they are hungry.”
Nishida and another scientist said they found male shrikes that consume more impaled food before the breeding season can chirp faster, which boosts their chances of attracting females.
The findings were published in the international ethology journal Animal Behavior.
Bull-headed shrikes were believed to impale grasshoppers and other prey on the tips of tree branches and elsewhere to store for winter, when food is scarce.
However, Nishida and his colleague examined the species’ behavior and discovered that male bull-headed shrikes eat almost all their impaled prey by January ahead of the opening of mating season.
February is frigid and food is scarce. Thus, if the practice of impaling their prey is part of their preparation for winter, the shrikes should eat as much in the month as they do in January.
But the scientists found that it wasn’t the case.
They also observed 14 male shrikes in the wild and looked for correlations between how much food they consumed and how many notes they sang per second.
Their results showed the more impaled prey the birds eat, the faster they can chirp. That’s likely because eating more helps boost the birds’ nutritional states.
Nishida and his colleague surveyed the successful mating rate of the species by changing the amounts of food in the birds’ territories. They found males that ate more were more likely to quickly find a mate.
The researchers’ thesis is available on the online version of the journal Animal Behavior at (https://doi.org/10.1016/j.anbehav.2019.04.002).
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