Photo credit: phys.org
Understanding Aggression in Cavity-Nesting Birds
“Get off my lawn!” While this phrase can evoke humor, it may also capture the essence of a female bird fiercely guarding her nest from intruders. A research team led by Sara Lipshutz from Duke University has uncovered significant insights into the aggressive behaviors of female birds that are obliged to nest in cavities.
These birds, referred to as obligate secondary cavity nesters, depend on pre-existing nooks in surfaces like tree trunks or rocky ledges for nesting, as they lack the ability to excavate cavities themselves. “Their reproductive success hinges on finding suitable holes, which makes these sites valuable resources worth defending,” Lipshutz explains.
The study concentrated on various bird families, including swallows, wood warblers, sparrows, thrushes, and wrens, analyzing two closely related species from each—one that nests in cavities and another that does not. Researchers deployed decoys and Bluetooth speakers that emitted the calls of each species to observe the resident birds’ reactions. The findings are documented in the journal Nature Ecology & Evolution.
Interestingly, aggressiveness in birds was found to be less about family lineage and more about nesting strategy. Typically, obligate cavity nesters manifested a higher disposition toward aggression compared to their more adaptable relatives. Notably, female cavity-nesters displayed heightened aggression over males, a behavior likely influenced by their stake in the nest’s survival.
“We observed a compelling behavioral trend,” remarked Lipshutz, noting the dynamics in competition leading to elevated aggression, particularly among females. “This tendency was pronounced.” Kimberly Rosvall, an alumna from Duke who contributed to the research, emphasized that the pressure to secure nesting sites was closely tied to this behavior.
The research also examined testosterone levels, which are often linked to aggression. Surprisingly, female cavity-nesting birds did not exhibit heightened testosterone compared to their counterparts. This lack of correlation raises new questions: if family ties and hormonal levels don’t fully explain the aggressive behaviors, could specific genetic expressions be at play?
The team investigated the gene expression patterns across the species included in their study to determine any common genetic markers associated with aggression. Although the results indicated that cavity-nesters shared many gene expression patterns, fewer genes consistently linked to aggression emerged across the different species.
“We anticipated identifying a small number of significant genes typically associated with aggression,” Lipshutz noted. “However, our results did not align with those expectations.” Yet, she remains optimistic about the implications of their findings. “Several hundred genes could be involved, functioning in nuanced ways. The diverse combinations that lead to similar aggressive behaviors are fascinating from an evolutionary standpoint.”
More information: Repeated behavioural evolution is associated with convergence of gene expression in cavity-nesting songbirds, Nature Ecology & Evolution (2025). DOI: 10.1038/s41559-025-02675-x
Citation: Many paths to an angry bird: Female cavity-nesting birds show higher aggression when defending limited nesting sites (2025, April 28) retrieved from Phys.org.
Source
phys.org