Moth Populations Surprisingly Propel Blue Tit Bird Numbers

In 2019, a joint study from seven research institutions reported that the number of birds in the United States and Canada  had fallen by 2.9 billion since 1970 . In other words, the population of birds had decreased by a staggering one-third over the preceding half century. This significant decline was particularly evident among familiar and cherished bird species: one-third of California quails had vanished, as well as almost half of all yellow-rumped warblers. These were birds that brought life to California and North America, and their alarming disappearance suggested a potential breakdown of the delicate balance of North America's ecosystem.

The question was, why?

A  study recently published in January 2024  sheds light on a possible contributor to bird population decline and growth. The research project specifically focuses on the population dynamics of the blue tit (Cyanistes caeruleus), a songbird commonly found in Eurasia. They wondered what factors affected blue tit populations. Was it increasing temperatures? Carbon emission levels? In fact, it was none of those. By assessing data spanning 23 years, researchers discovered that the mass disappearance of blue tits was largely determined by one factor: the abundance of moths. Specifically, when moths are plentiful, there is a significant increase in blue tit populations the following spring and summer.

Dr. Luke Evans, the lead author of the study at the University of Reading, hypothesizes that this correlation is likely due to the fact that moths are a primary component of the blue tit’s diet. Thus, elevated moth populations provide blue tits with ample resources for feeding and breeding. “Insect abundance directly impacts songbird numbers from year to year,” Evans explains. “When moth caterpillars are large in number, blue tit parents can easily find food for their demanding chicks. When moth numbers crash it gets much harder for birds to find enough insects and raise as many young.”

The importance of food availability for the continued survival of bird species isn’t a newfinding. In fact, the relationship between flourishing insect prey populations and predator bird populations is a classic example of predator-prey relationships, a concept frequently covered in high school biology courses. What is novel about this research study, however, is two-fold.

First, the study precisely pinpoints the moth species that play a crucial role in the survival of the blue tit population. Among all moths, the most impactful were winter moths, which are known to be the primary food source for blue tits given that they emerge during the spring months, coinciding with the blue tit’s breeding season. By understanding which food sources are most necessary for the survival of bird species, conservation biologists are better equipped with the knowledge needed to prioritize the preservation of specific prey species to most effectively safeguard bird populations.

Secondly, this study marks a pioneering approach that can serve as a framework to address the larger problem of declining bird populations more broadly. The data for this research project was gathered through two expansive datasets: the Rothamsted Insect Survey, which has been tracking moth populations since the late 1960s, and the Breeding Bird Survey, which uses crowdsourced data from volunteers across the UK. By being the first large-scale study of its kind to merge these two datasets and devise an algorithm to assess their interrelation, this was noteworthy demonstration of the insights achievable when monitoring data for different species are consolidated. This methodology can be extended to a diverse range of bird species and aid in the identification of vulnerable sites across ecosystems.

Moreover, this research highlights the urgent need for integrated conservation strategies that address both predator and prey species. Conservation efforts often focus on protecting charismatic or flagship species, but the findings of this study suggest that ensuring the survival of crucial insect populations is equally important. Effective conservation strategies should thus include measures to maintain healthy insect communities, such as reducing pesticide use, preserving natural habitats, and supporting biodiversity-friendly agricultural practices.

The successful integration of the Rothamsted Insect Survey and the Breeding Bird Survey datasets also sets a precedent for future research. By demonstrating the value of combining long-term datasets and utilizing innovative analytical approaches, this study provides a model for how to tackle complex ecological questions. Future research can build upon this framework, applying similar methodologies to other species and ecosystems to uncover hidden patterns and relationships that might inform conservation efforts.

In short, this study isn’t just about the blue tit or the winter moth; it reveals a deeper story about how every part of our ecosystem is connected. In the context of the delicate balance of nature, where each species plays a crucial role, from tiny moths to vibrant birds, researchers have given us a valuable new way to understand and protect our environment. This perspective challenges us to see our own role in this intricate web. As we face ongoing environmental issues, we have the opportunity to not just watch but actively shape the outcome of this unfolding story. If we’re not careful, we might miss the chance to address these challenges before it’s too late.

Original Article:    https://doi.org/10.1111/ele.14362