This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: As they build their nests, many birds are known to interweave dried grasses and other materials with green plants, such as fresh leaves, grass stems, herbs and aromatic leaves. While this behavior is well documented, why many bird species choose to add fresh plants has remained unclear.
Some scholars have suggested that green nest material serves as a courtship signal that can attract potential mates. Others have proposed that it can protect birds and their offspring from harmful parasites or pathogens, improving their health. Researchers at Bielefeld University in Germany recently combined and analyzed evidence from earlier studies to shed more light on the possible reasons many birds decorate their nests with fresh plants.
Their paper, published in Proceedings of the Royal Society B: Biological Sciences, suggests that green nest material can boost birds' fitness, though more studies are needed to clearly elucidate its benefits. "Our interest in nests began with coming across studies showing that nests can be much more than structures in which birds lay their eggs and raise their young," Shreya Dimri, first author of the paper, told Phys.org. "One study that particularly fascinated us described male black wheatears carrying, on average, almost two kilograms (4.4 pounds) of stones to their nest cavities before a clutch is laid.
I would say this is an extraordinary investment for such a small bird that may serve as a sexually selected display." While reviewing past literature, Dimri and her colleagues also found a paper suggesting that great spotted cuckoos (Clamator glandarius), which are known to lay eggs in nests built by birds of another species, often choose the larger nests of magpies (Pica pica). This observation may suggest that they perceive nest size as an indicator of the parenting ability of the bird that built it. "These examples and many more force us to think of nests not simply as places where reproduction happens," said Dimri.
"They can be an extended expression of the birds themselves and convey information to potential mates, competitors or even other species. Over time, through talks and discussions at conferences, this drew our attention to another fascinating behavior in which some birds repeatedly bring fresh leaves, herbs or sprigs, often from aromatic plants, to their nests." While many researchers have tried to explain why some birds add green plants to their nests, the results of past studies have been mixed and inconclusive. Dimri and her colleagues tried to uncover these reasons by combining and collectively analyzing a large pool of previous results.
"We became quite curious, and we wanted to answer two main questions: Does green nest material provide measurable benefits to birds, and, if so, which of these proposed mechanisms best accounts for those benefits?" said Dimri. "Our lab works largely in evidence synthesis, bringing together results from many individual studies to determine what the literature shows as a whole, why findings sometimes differ, and where important knowledge gaps remain. We thus conducted a systematic review followed by a meta-analysis, which can be a powerful tool to combine results from multiple studies." The researchers first identified past studies in which scientists had added or removed green material from bird nests, then observed the effects on the birds.
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