Female whiskered terns deceive strange males to get food

Some female whiskered terns deceive strange males to get extra food. These females offer copulation in return for food, but ultimately do not allow it. Until now, similar situations in the bird world have not been known, researchers say.

Whiskered terns were observed for two years on carp ponds of the Institute of Inland Fisheries near Zator. It is a Natura 2000 area - the Valley of Lower Skawa.

It turns out that female whiskered terns deceive strange males to get extra food.

"Females offer copulation in exchange for a gift. But they do not behave fairly, and although at first they encourage strange males, later they take away their food and do not allow them to copulate" - says Dr. Mateusz Ledwoń from the Institute of Systematics and Evolution of Animals PAS in Kraków, author of observations. Grzegorz Neubauer from the University of Wrocław was also involved in the study.

In practice, some of the observed females, seeing a strange male nearby, invite the male to copulate by raising the rump and making a specific call. Holding the gift in its beak, the male jumps onto the back of the female and attempts to copulate. "Using the moment of the male`s distraction, the female immediately turns her head, grabs the food and chases the male away, preventing copulation" - the ornithologist describes.

"In many species of birds studied in this respect, females - in exchange for different kinds of gifts, food or nest material - allowed copulation with a strange male. Female whiskered terns are an exception. They do not have to mate with strange males to get extra food They simply trick them" - emphasises Dr. Ledwoń.

According to Ledwoń, the success rate in obtaining food with fraud was high, amounting to 70 percent. To compare, the success associated with getting food from a strange male in a situation where the female tried to snatch food immediately after his arrival (without attempting to deceive the male), amounted to only 1 percent.

Ornithologists estimate that in the population they studied, 30-40 percent females obtained additional food this way. Why were others not doing it? Dr. Ledwoń believes that they either have not learnt to cheat, or they simply ... were not that hungry.

"For the females that were insufficiently fed by their own partners, the food gained through deception covered even several dozen percent of their food demand" - he adds.

Researchers estimate that only 0.7 percent visits of males trying to get copulation in exchange for food actually succeed.

"It appears that in conditions of abundance of food in carp ponds, the loss of males as a result of female fraud does not adversely affect their own condition or the condition of their female partners" - the researcher says.

This behaviour of females is the first known case of such fraudulent behaviour in the bird world, emphasise the authors of the publication on this behaviour, which appeared in the "Journal of Avian Biology".

Whiskered tern is a water-marsh bird, nesting in colonies on water reservoirs. A few weeks before laying eggs, females spend most of their time in nests. They save the energy needed to lay three eggs, which make up a significant proportion of their body weight. Males spend most of their time feeding and bringing their females food: fish, tadpoles and dragonflies.

"During that time, males also try to copulate with other females. Copulation with a non-partner is a great advantage for every male, because it creates an opportunity to become a father of chicks, which will be taken care of by another male. For females, copulation with a strange male has many negative consequences. For example, when +dating+, females risk their partner`s revenge" - concludes the scientist. (PAP)

author: Szymon Zdziebłowski

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