Scientific American - USA (2020-12)

December 2020, ScientificAmerican.com 19

ANIMAL BEHAVIOR

Bird Battles

Scientists have company watching woodpecker combat

The Americas’ western oak woodlands are fragmented into fiercely contested territories by cadres of acorn woodpeckers, each guarding “granary” oaks storing thousands of acorns. The birds nest in groups that cooperatively raise chicks; when one member of a breeding pair in a granary-rich turf dies, rival teams of nonbreeding birds swoop in from surrounding areas to fight for the spot. These sometimes deadly struggles can last for days. Scientists have studied the skir- mishes for over 50 years—but they only recently learned that other woodpeckers are keenly observing the battles, too. Smithsonian biologist Sahas Barve led a study of these fights that was published in Current Biology. His group discovered the spectators by fitting dozens of birds with ultralight solar-powered radio track- ers. “Power struggles are so chaotic that you can’t [visually] track the movements of any one animal,” Barve says. Biologists have seen news of a breeding opportunity travel with astonishing speed. “Because animals don’t have lan- guage, we often assume it’s harder for them to transmit information,” says Princeton University evolutionary biologist Christina Riehl, who was not involved in the study. “They’re not posting about it on Face book or talking about it in the streets.” Nobody yet knows how birds in surrounding territories find out so quickly, sometimes triggering battles in minutes. Barve’s group saw that combat draws not only fighters but also birds that come to watch for up to an hour. These viewers leave their own granaries undefended, which suggests intelligence gained about rival groups is worth the risk, Riehl says. Monitoring the relationships between individuals in other groups is rarely seen among birds, Barve says. The study shows that the woodpeckers “have a very high-level understanding of social dynamics in their population,” he adds. “It highlights how much we don’t know about how animals perceive and navigate a complicated social system.” — Jim Daley

tion exposure at those estimated levels to deleterious genetic, physiological and repro- ductive effects, Mousseau says. “This work is very important and is well done,” says Carmel Mothersill, a radiobiolo- gist at McMaster University in Ontario, who was not involved in the study. “My own lab has used this approach to reanalyze data from Fukushima as well as Chernobyl, and it gives a much more meaningful relation between radiation exposure and risk of harm.” But according to University of Georgia wildlife ecologist James Beasley, a co-author of past conflicting studies, the paper suffers from “critical flaws”—primarily in how the authors estimated animal abundance. Their original measurement locations, he says, were not spaced appropriately or extensively enough to draw conclusions about the entire area. Karine Beaugelin-Seiller, study lead author and a radioecologist at the Institute for Radiological Protection and Nuclear Safety in France, agrees that uncertainty remains. Yet, she says, the study provides a more accurate way to establish the connec- tion between radiation exposure and effects, ideally guiding future research. — Rachel Nuwer

December 2020, ScientificAmerican.com 19

ANIMAL BEHAVIOR

Bird Battles

Scientists have company watching woodpecker combat

The Americas’ western oak woodlands are fragmented into fiercely contested territories by cadres of acorn woodpeckers, each guarding “granary” oaks storing thousands of acorns. The birds nest in groups that cooperatively raise chicks; when one member of a breeding pair in a granary-rich turf dies, rival teams of nonbreeding birds swoop in from surrounding areas to fight for the spot. These sometimes deadly struggles can last for days. Scientists have studied the skir- mishes for over 50 years—but they only recently learned that other woodpeckers are keenly observing the battles, too. Smithsonian biologist Sahas Barve led a study of these fights that was published in Current Biology. His group discovered the spectators by fitting dozens of birds with ultralight solar-powered radio track- ers. “Power struggles are so chaotic that you can’t [visually] track the movements of any one animal,” Barve says. Biologists have seen news of a breeding opportunity travel with astonishing speed. “Because animals don’t have lan- guage, we often assume it’s harder for them to transmit information,” says Princeton University evolutionary biologist Christina Riehl, who was not involved in the study. “They’re not posting about it on Face book or talking about it in the streets.” Nobody yet knows how birds in surrounding territories find out so quickly, sometimes triggering battles in minutes. Barve’s group saw that combat draws not only fighters but also birds that come to watch for up to an hour. These viewers leave their own granaries undefended, which suggests intelligence gained about rival groups is worth the risk, Riehl says. Monitoring the relationships between individuals in other groups is rarely seen among birds, Barve says. The study shows that the woodpeckers “have a very high-level understanding of social dynamics in their population,” he adds. “It highlights how much we don’t know about how animals perceive and navigate a complicated social system.” — Jim Daley

tion exposure at those estimated levels to deleterious genetic, physiological and repro- ductive effects, Mousseau says. “This work is very important and is well done,” says Carmel Mothersill, a radiobiolo- gist at McMaster University in Ontario, who was not involved in the study. “My own lab has used this approach to reanalyze data from Fukushima as well as Chernobyl, and it gives a much more meaningful relation between radiation exposure and risk of harm.” But according to University of Georgia wildlife ecologist James Beasley, a co-author of past conflicting studies, the paper suffers from “critical flaws”—primarily in how the authors estimated animal abundance. Their original measurement locations, he says, were not spaced appropriately or extensively enough to draw conclusions about the entire area. Karine Beaugelin-Seiller, study lead author and a radioecologist at the Institute for Radiological Protection and Nuclear Safety in France, agrees that uncertainty remains. Yet, she says, the study provides a more accurate way to establish the connec- tion between radiation exposure and effects, ideally guiding future research. — Rachel Nuwer

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