General population study shows that BMI classification system wrongly identifies some people as having overweight or obesity

Use of gold standard dual-energy X-ray absorptiometry (DXA) to measure body fat shows BMI places many people in the wrong weight category

European Association for the Study of Obesity

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Research from Italy to be presented at this year’s European Congress on Obesity (ECO 2026, Istanbul, Turkey, 12-15 May) and published in the journal Nutrients shows that when the gold standard technique of dual-energy X-ray absorptiometry (DXA) is used to measure body fat in the general population, it shows that the traditional WHO body mass index (BMI) classification system misidentifies significant numbers of people as having overweight or obesity. 

In the past few years there has been a lot of criticism of the BMI system due to its inability to accurately capture body fat percentage or distribution, in order to correctly categorise weight status based on adiposity explains Professor Marwan El Ghoch, of the Department of Biomedical, Metabolic and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy.  He adds that, despite these concerns, BMI as a weight classification system continues to be used in the general population in primary healthcare (i.e. general practitioners) and non-clinical (i.e. policy and health insurance) settings.

In this new study, Professor El Ghoch and researchers from the University of Verona in Italy and Beirut University in Lebanon set out to determine the validity of the BMI classification system, specifically regarding its ability to identify correctly those with overweight and obesity, in a sample of the general population who had all had their body fat measured using DXA. With DXA, the person’s age and body fat percentage is used to decide their weight status category according to their level of adiposity.*

The study included 1351 adults of mixed gender aged between 18 and 98 years (60% female) all of whom were referred to the Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy. All the participants in this study where White Caucasian (due to BMI variations in different ethnicities).

According to the WHO BMI system, among these participants there were 19 (1.4%) underweight individuals (BMI under 18.5), 787 (58.3%) normal weight (BMI 18.5-25), 354 (26.2%) with overweight (BMI 25-30), and 191 (14.1%) with obesity (BMI over 30). The overall prevalence of approximately 41% for overweight and obesity combined is consistent with the local population in the Veneto region of Italy. Participants were then re-categorised according to adiposity based on body fat percentage (BF%) measured by DXA.

DXA revealed that more than one third (34%) of those with obesity defined by BMI had been misclassified and should be in the overweight category. For those with an overweight BMI, DXA showed that more than half – 53% – had been misclassified – three quarters of those misclassified fall into the normal weight category, while the other quarter should have been classified as having obesity.

BMI and DXA had better agreement when considering those with a normal weight BMI (18.5 to 25), with DXA agreeing in 78% of cases. But 22% of those with normal weight were given a different category with DXA (9.7% underweight, 11.4% overweight and 0.8% obesity). Finally, despite the small absolute numbers, the biggest BMI-DXA disagreement was found in the underweight group - two thirds (13 of 19; 68.4%) in the underweight category defined by BMI (under 18.5) were in the wrong category when analysed by DXA - and should have been classified as having normal weight.

With all the correct and misclassifications combined, the DXA analysis found that the prevalence of overweight and obesity across the cohort was at around 37% overall (23.4% overweight, and 13.2% obesity, compared to 26.2% and 14.1% with BMI).

Professor El Ghoch, who led the study, says: “Our main finding highlights the fact that a large proportion of individuals, exceeding one-third of adults among the Italian general population, is misclassified and placed in an incorrect weight status category, when relying on the traditional WHO BMI classification resulting in an overestimation of the prevalence of underweight, overweight, and obesity when compared to the classification based on body fat percentage as measured by the gold standard technique of dual-energy X-ray absorptiometry (DXA).”

Study co-author, Professor Chiara Milanese, of the University of Verona, adds: “Another key finding of our study is that, even though both systems identify a similar overall prevalence of overweight and obesity,  we are talking in some cases about different people - or in other words the individuals identified by DXA are not all the same as those from BMI classification. This is due to the disagreement between WHO BMI and DXA-derived BF% classification systems in determining weight status in the general population among body weight ranges and age groups of both genders.”

Accordingly, the authors conclude: “Public health guidelines in Italy need to be revised to consider combining direct body composition or their surrogate measures such as skinfold measurement or body circumference - such as the waist-to-height ratio - with BMI while assessing weight status in the general population. We believe a similar level of misclassification can be expected in White Caucasian populations in other countries in Europe and Worldwide. However, to confirm this, and if a similar effect exists in other ethnicities, future research should extend the aim of our analysis to other countries across Europe and globally, as well as seeing if such misclassification occurs in people of other ethnicities.”

Professor Marwan El Ghoch, University of Modena and Reggio Emilia, Modena, Italy. T) +39 0592055371 E) m.elghoch@unimore.it

Tony Kirby in the ECO Media Centre. T) +44 7834 385827 E) tony.kirby@tonykirby.com

The authors confirm no conflicts of interest.

This press release is based on oral presentation 0360 at the European Congress on Obesity (ECO) in Istanbul, Turkey, 12-15 May. The material has been peer reviewed by the congress selection committee. The full paper has been published in the journal Nutrients. As such, the full paper is provided in place of the abstract.

Notes to editors:

The following thresholds are used in DXA – body fat values to give weight status:

For males:

18–39 years BF% < 8% (underweight); ≥8% (normal weight); ≥21% (overweight); ≥26% (obesity); 40–59 years BF% < 11% (underweight); ≥11% (normal weight); ≥23% (overweight); ≥29% (obesity) 60–98 years BF% < 13% (underweight); ≥13% (normal weight); ≥25% (overweight); ≥31% (obesity).

For females:

18–39 years BF% < 21% (underweight); ≥21% (normal weight); ≥33% (overweight); ≥39% (obesity); 40–59 years BF% < 23% (underweight); ≥23% (normal weight); ≥35% (overweight); ≥41% (obesity); 60–98 years BF% < 26% (underweight); ≥26% (normal weight); ≥36% (overweight); ≥41% (obesity).

For full paper, click here

For link to full paper to use in your stories, click here

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Journal

Nutrients

Article Title

The WHO BMI System MisclassifiesWeight Status in Adults from the General Population in North Italy: A DXA-Based Assessment Study (18–98 Years)

 

Global maternal deaths fell to 240,000 in 2023, but more than 100 countries still fall short of the global maternal mortality target as progress slows worldwide

Institute for Health Metrics and Evaluation

• The maternal mortality ratio in 2023 remained nearly three times higher than the United Nations’ Sustainable Development Goal (SDG) target 3.1 for 2030. 

• New estimates through 2023 show global maternal mortality progress slowed between 2015 and 2023 compared with 2000–2015. 

• Maternal hemorrhage and hypertensive disorders of pregnancy together account for more than 40% of maternal deaths globally, highlighting the need for improved access to quality maternal care. 

SEATTLE, Wash. – March 26, 2026 – Global maternal deaths have declined over the past three decades, yet progress has slowed in recent years and remains uneven across countries, according to new Global Burden of Disease (GBD) 2023 research published today in The Lancet Obstetrics, Gynaecology, & Women’s Health. 

The study estimates that 240,000 women died from maternal causes in 2023, accounting for 5.5% of all deaths among women aged 10-54 worldwide. Maternal deaths remain concentrated in regions facing the greatest health system and data challenges, particularly across sub-Saharan Africa, Oceania, South Asia, Southeast Asia, and parts of the Caribbean. In 2023, Nigeria, India, the Democratic Republic of the Congo, Ethiopia, and Pakistan recorded the highest numbers of maternal deaths worldwide. 

The analysis, led by researchers at the Institute for Health Metrics and Evaluation (IHME) at the University of Washington and collaborators worldwide, provides the most up-to-date global assessment of maternal mortality trends across 204 countries and territories through 2023, including subnational estimates for 20 countries. The study incorporates more than 1,000 newly available data sources and updated modeling approaches, and also provides updated estimates of causes of maternal death, progress toward global targets, and trends during and after the COVID-19 pandemic. 

Progress toward maternal mortality targets has slowed in many countries. 

While the global maternal mortality ratio declined by more than one-third, from 321 maternal deaths per 100,000 live births in 1990 to 191 in 2023, it remains far above the SDG target as progress has slowed in recent years. Maternal mortality fell more rapidly between 2000 and 2015, when maternal mortality ratios declined by nearly 3% per year on average. Since 2015, however, progress has slowed considerably, with global declines averaging only about 0.5% per year and some countries experiencing increases in maternal mortality. 

In 2023, the highest maternal mortality ratios were observed across the four regions of sub-Saharan Africa, as well as parts of the Caribbean and Oceania. Countries with particularly elevated rates included Liberia, the Central African Republic, Haiti, Eritrea, and Sierra Leone. 

Table: Countries with the highest maternal mortality ratios, 2023 

Country	Maternal mortality ratio (maternal deaths per 100,000 live births)
Liberia	1,210
Central African Republic	865
Haiti	819
Eritrea	768
Sierra Leone	762
Chad	728
Democratic Republic of the Congo	713
Cameroon	661
Guinea	626
Gabon	586

 

“While the world made impressive strides in reducing maternal mortality after 2000, momentum has slowed since 2015 and, in some places, has started to regress. To reverse this trend, health systems must strengthen access to quality care before, during, and after pregnancy, particularly in countries where maternal mortality remains highest,” said Dr. Mae Dirac, senior author and Assistant Professor of Health Metrics Sciences and Family Medicine. 

Leading causes of maternal deaths remain largely preventable. 

The study shows that the leading causes of maternal deaths vary by location but remain well known and largely preventable, with maternal hemorrhage and hypertensive disorders of pregnancy responsible for the largest share of deaths globally. Improvements in access to antenatal care, safe delivery services, emergency obstetric care, and post-partum follow-up could substantially reduce mortality, especially in countries with the highest burdens.  

However, many high-burden regions remain data-sparse, making it harder to track progress and respond quickly to emerging challenges. Expanding high-quality vital registration, maternal death surveillance, and local data systems will be critical to guide effective policy and investment. 

“Maternal mortality is both a health system challenge and a reflection of broader inequities affecting women’s health,” said Ira Martopullo, co-lead author and a PhD candidate in Global Health Metrics at the University of Washington and IHME. “In some countries, progress has followed economic growth and expanded health resources. Others, including Ethiopia, Bangladesh, Nepal, and Cambodia, have reduced maternal deaths by expanding access to facility-based delivery and strengthening maternal health services despite ongoing resource limitations.” 

Pandemic disruptions temporarily increased maternal deaths in some regions. 

Beyond the known causes of maternal death, COVID-19 infection also led to increases in maternal mortality early in the pandemic. During 2020 and 2021, prior to widespread vaccination, COVID-19 caused temporary increases in maternal deaths in several regions, particularly in locations with high COVID-19 mortality. Increases were observed across parts of Latin America and the Caribbean, Central and Eastern Europe, Central Asia, and high-income North America, temporarily reversing progress in some countries that had previously been approaching SDG targets.  

Globally, the maternal mortality ratio remained relatively stable during the peak pandemic years, but health system disruptions and increased infection risks during pregnancy contributed to setbacks in several locations. In most places with data available through 2022 and 2023, maternal mortality returned toward pre-pandemic trends, highlighting both health system resilience in some settings and vulnerability in others. 

While some locations have returned to pre-pandemic maternal mortality trends, levels remain far above global targets in many parts of the world. With less than five years remaining to meet SDG target 3.1, renewed global action and sustained investment will be needed to accelerate progress, strengthen health systems, and improve countries’ ability to monitor and reduce maternal mortality. 

For interviews with the authors, please contact IHME’s Media Team at ihmemedia@uw.edu. 

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Journal

The Lancet

DOI

10.1016/S3050-5038(26)00047-6 

Subject of Research

People

Article Title

Global, regional, and national levels and trends in maternal mortality, progress towards the Sustainable Development Goals, and mortality from COVID-19 infection in pregnant women, 1990–2023: a systematic analysis for the Global Burden of Disease Study 2023

Article Publication Date

26-Mar-2026

 

The Lancet Neurology: Over 250,000 deaths from meningitis globally in 2023; over one third in children under five, suggests most comprehensive global assessment to date

The Lancet

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In 2023, globally 259,000 people died from meningitis and 2.5 million people were infected with the disease, suggests a study published in The Lancet Neurology. Although death and infection rates have declined significantly since 1990, progress is insufficient to meet the WHO targets of a 50% reduction in infections and 70% reduction in deaths by 2030.  
 
Meningitis is the leading infectious cause of neurological disabilities globally. Since 2000, widespread global vaccine rollout has greatly reduced the number of infections and deaths in both high-income and low-income countries, however progress lags behind other vaccine-preventable diseases. 
   
This study provides the most comprehensive global assessment of meningitis to date. It suggests globally 259,000 people died from meningitis and 2.5 million people were infected with the disease in 2023, with the greatest risk factors for deaths being low birthweight followed by premature birth and air pollution (both household and atmospheric). The burden of disease remained disproportionately high in low-income countries, particularly in the African meningitis belt, where Nigeria, Chad, and Niger recorded the highest death and infection rates. Streptococcus pneumoniae, Neisseria meningitidis, non-polio enteroviruses, and other viruses were the leading causes of death, while non-polio enteroviruses caused the most cases. 
 
Authors say greater efforts, including expanding vaccination programmes, greater antibiotic stewardship, improving access to care, and strengthening diagnostics and monitoring for meningitis, are essential to achieve further reductions in the disease globally. 
 

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Journal

The Lancet Neurology

DOI

10.1016/S1474-4422(26)00101-8 

Method of Research

Observational study

Subject of Research

People

Article Title

Global, regional, and national burden of meningitis, its risk factors, and aetiologies, 1990–2023: a systematic analysis for the Global Burden of Disease Study 2023

Article Publication Date

27-Mar-2026

 

Masripithecus: A new Miocene ape from Egypt sheds light on the origins of modern apes

A 17–18-million-year-old ape from Egypt suggests that the Middle East was a key center in early hominoid evolution

Mansoura University Vertebrate Paleontology Center (MUVP)

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Reconstruction of Masripithecus moghraensis by Mauricio Antón.

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Credit: Copyrights belong to Professor Hesham Sallam

In a study to be published in Science on [3/26/2026], an international research team from the Mansoura University Vertebrate Paleontology Center (Egypt) and the University of Southern California (USA) describe Masripithecus moghraensis, a newly identified fossil ape that lived around 17–18 million years ago, during the Early Miocene. Recovered from the Wadi Moghra fossil site in northern Egypt, the remains represent the first definitive fossil ape known from North Africa. The finding not only extends the geographic range of early apes, but also places Egypt—and the wider Middle East region—at the heart of a pivotal evolutionary transition leading to modern apes.

Hesham Sallam, a paleontologist at Mansoura University, Egypt, and senior author of the study, said, “We spent five years searching for this kind of fossil because, when we look closely at the early ape family tree, it becomes clear that something is missing—and North Africa holds that missing piece.”

Previously, Early Miocene sites in North Africa had yielded fossils of monkeys, but not apes. As a result, early apes and their close relatives were thought to be confined largely to more southern parts of Africa during this period. Geologically younger ape fossils have been reported from Africa, Asia, and Europe, but their relationships and geographic roots are actively debated. Now it appears likely that this uneven fossil record obscured our understanding of the origin of crown Hominoidea—the group that includes all living apes, from gibbons and orangutans to gorillas, chimpanzees, and humans, along with their last common ancestor.

The discovery of Masripithecus not only reveals that apes were present in North Africa during this time period, but also that the new species was quite distinct from similar-aged species in East Africa. The genus name Masripithecus combines Masr (مصر), the Arabic word for Egypt, with the Greek píthēkos, meaning ape. The species name refers to Wadi Moghra, a well-known fossil locality in northern Egypt, where the remains were recovered during fieldwork by the Sallam Lab team in 2023 and 2024.

Although the new fossil material is limited to the lower jaw, it preserves a distinctive combination of features not seen in any other known ape from this time. These include exceptionally large canine and premolar teeth, molar teeth with rounded and heavily textured chewing surfaces, and a notably robust jaw. “Together, they suggest that Masripithecus was adapted for versatility. The study interprets its chewing anatomy as evidence of a flexible, mainly fruit-based diet, with the ability to process harder foods such as nuts or seeds when needed. This flexibility would have helped Masripithecus to thrive at a time when climatic changes were leading to more pronounced seasonality in northern Africa and Arabia,” said Shorouq Al-Ashqar, a researcher at the Mansoura University Vertebrate Paleontology Center, Egypt who was a first author of the study.

Anatomy alone, however, is only part of the story. Masripithecus occupies a key position on the ape family tree. Using sophisticated Bayesian methods, the team combined anatomical evidence from living and extinct apes, DNA from living apes, and the geological ages of fossil species to determine how living and extinct species are related, and when they all split from each other. The researchers’ analysis found that Masripithecus is more closely related to the living apes than are any species known from the Early Miocene of East Africa.

Additional biogeographic analyses by the team point to northern Africa and the Middle East as the most likely home for the common ancestor of all living apes, which is estimated to have lived during the Early Miocene. During that time period, this region occupied a key position as the African and Arabian plates moved to the north during their final phase of collision with Asia. Shifting sea levels periodically reduced marine barriers, turning the region into a natural corridor for animal dispersal.

In this context, Masripithecus provides a crucial intermediate link between the previously disjunct African and Eurasian fossil records, revealing that apes were already diversifying in the area and therefore positioned to expand into Europe and Asia as soon as land connections were established.

Erik Seiffert, a paleontologist at the University of Southern California who was a co-author of the study, said that his perspective on ape origins has changed. “For my entire career, I considered it probable that the common ancestor of all living apes lived in or around East Africa. But this new discovery, and our new and novel analyses of hominoid phylogeny and biogeography, now strongly challenge that idea. And, importantly, the likelihood of this scenario doesn’t depend on Masripithecus -- but it is very much consistent with it.”

The researchers anticipate that renewed exploration in this region will uncover further fossils critical to understanding the origin and early diversification of modern apes. As Masripithecus moghraensis shows, key chapters of our evolutionary history may still lie hidden in regions that have yet to be fully explored.

Masripithecus: A new Miocene ape from Egypt sheds light on the origins of modern apes [VIDEO] 

 

Masripithecus moghraensis mandibular fragment with right M3 at the moment of discovery.

Credit

copyrights belong to Professor Hesham Sallam

Sallam Lab team from Mansoura University Vertebrate Paleontology Center

Credit

copyrights belong to Professor Hesham Sallam

Masripithecus: A new Miocene ape from Egypt sheds light on the origins of modern apes [VIDEO] 

Masripithecus sculpting video, sculpting by Mohammed Hebeish

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Journal

Science

DOI

10.1126/science.adz4102 

Subject of Research

Not applicable

Article Title

An Early Miocene ape from the biogeographic crossroads of African and Eurasian Hominoidea

Article Publication Date

26-Mar-2026

 

Study in search of a tropical spring is the first to show some birds flip their breeding season in response to climate

Florida Museum of Natural History

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Scientists know comparatively little about the breeding seasons of tropical birds. This point is underscored by a new study that shows insect-eating birds in the tropics can postpone breeding by nearly half a year, more than four times as long as previously observed.

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Credit: Photo by Felicity Newell

Key points

• Many years of scientific observation and research show that temperate birds nest in the spring, and their breeding seasons rarely vary by more than a few days from year to year for any given species

• In contrast, scientists know little about the breeding seasons of tropical birds. The information that does exist suggests that species may shift their breeding times by up to one month at a given site.

• The recently published results of a five-year field study show that this variation has been drastically underestimated in tropical mountains, where — in some cases — whole chunks of the community can breed in opposite seasons in response to shifting climates and resource availability.

In 2014, Felicity Newell joined the Florida Museum of Natural History as a doctoral student, then promptly left the country in search of a tropical spring. It’s a concept she started thinking about while doing biological surveys in Honduras. There, a colleague told her about the work of Alexander Skutch, a renowned ornithologist who spent 20 years studying the breeding habits of birds in Costa Rica. Based on this work, he became “convinced that the birds … have a definite nesting season, and its beginning coincides with the return of spring.”

Costa Rica is a tropical country 9 degrees north of the equator, and as such, it does not have the spring and winter seasons associated with temperate regions. Its climate is balmy year-round, which — Skutch noted — gave people “…the impression that, with tropical birds, singing and nesting continue freely throughout the year.”

Skutch combined the observations he’d made over 20 years with those from other naturalists and determined that this was not the case. Tropical birds, it seemed, primarily nested when their resources were abundant. For birds that eat insects, called insectivores, this occurred from March through June, aligning with the spring breeding season of birds further north. Hence, the concept of a tropical spring.

Back in Honduras, Newell was intrigued. She read up on similar studies to see what had been learned since Skutch’s initial discovery, which he’d published in 1950. But research on the breeding habits of tropical birds was scarce. Much of the work that had been done was anecdotal, lacking data on rainfall and other climate variables and often combining all the observations from a particular country or region. That meant that any local variation in breeding times would be effectively invisible.

“I realized we actually didn’t know how the whole ecosystem worked at all,” Newell said. So she decided to conduct her own study, developing a new project from scratch on tropical montane birds with colleague Ian Ausprey; both Newell and Ausprey are now asisstant professors at Texas A&M University, and were advised by study co-author Scott Robinson, the Ordway eminent scholar at the Florida Museum.

They found a spot in the cloud forests of northern Peru where they lived with local families and communities and collected data for the next five years.

“It was a massive undertaking,” Newell said. “We’d leave before it was light and spend 12 hours in the fields, hiking up mountains in the mud and rain, often getting back after dark. We worked with over 20 field assistants, many from across Peru and Latin America.”

An important decision they had to make early on was how to go about monitoring birds and how to distinguish between those that were breeding and those that weren’t. The obvious and most direct strategy would be to locate nests, which Newell had gotten good at while studying migratory songbirds in the Appalachians. This type of work is long and arduous, but it initially suited Newell just fine.

“I’m kind of obsessed with nests. Actually, that was the original goal of the study, to spend more time looking for nests. But then I realized I didn’t even know when the birds were nesting, and I didn’t have 20 years to find out like Alexander Skutch.” She also had a lot more ground to cover. While Skutch had mostly stuck to one spot, Newell and Ausprey were sampling on eight separate mountains over an area spanning more than 60 miles.

So they settled on mist nets, a reliable and widely used tool among ornithologists everywhere, though they still made note of any nests that they could find.

After netting a bird, they looked for any signs of recent breeding, such as the downy feathers of juvenile birds or a cloacal protuberance on males, which would indicate their readiness to mate. If they had a female, they’d search for a brood patch, which forms when they “lose the feathers on their abdomen, which becomes more vascularized to help incubate the eggs,” Newell said.

Newell wanted to know when tropical birds were nesting, but she also wanted to know what environmental factors were correlated with breeding. So she, Ausprey and the field assistants also measured the abundance of flowers and fruit, recorded rainfall and collected insect biomass data by “vigorously beating the nearest shrub several times over a sweep net.”

At the end of five years, they’d captured and released more than 8,000 birds, documented nearly 4,000 breeding events (such as the presence of juveniles), collected 48,000 insects and found 318 nests.

Finally, they conducted analyses to determine how all of these factors influenced each other. The results caught Newell off guard.

“I wasn’t expecting this amount of variation,” she said. In temperate regions, she explained, the start of the nesting season for a given species can vary annually by three to five days. Research done in the tropics suggested breeding times could vary by a few weeks, potentially even a month. What Newell found was much more than that.

“There was a massive amount of variation, and not just in individual species. Whole chunks of the community were shifting, both spatially and temporally in different ways.”

Tropical environments may not have a true spring, but they do have pronounced wet and dry seasons. Skutch found that most of the birds at his site nested at the tail end of the dry season, just as the rains were beginning to return, stirring plants from their torpor as they busily transformed water into fresh, new leaves, and insects turned those leaves into chitin, hemolymph and viscera. Skutch likened this flush of activity to spring, but the reality is more nuanced and complex.

To tease apart the subtleties, Newell divided the birds into three groups based on their diet: nectarivores, frugivores and insectivores.

The first two groups had fairly predictable patterns that aligned with previous data. Nectar drinkers, like hummingbirds, built nests at the beginning of the dry season, when bird-pollinated flowers were in bloom. Fruit-eating birds, such as tanagers, built their nests during the wet season, when fruit was abundant.

But insectivores couldn’t seem to make up their mind.

“They might breed in June in one year, and if the next year was dry they would breed in May, so they’re varying temporally by about a month,” which isn’t particularly unusual, she said. “However, within 60 miles of each other, one insectivore community might breed in May and the other community might breed in October.”

That was unusual. No other study had shown that tropical birds could put off breeding by nearly half a year.

The point at which a community seesawed between seasons was strongly correlated with insect abundance, to the extent that Newell could pinpoint the average weight of insect biomass at which the scales tipped; 43 milligrams per square meter was the magic number. If the average weight of insects in a square meter remained adequate during the dry season across decades, insect-eating birds would nest as rain tapered off; anything below that number, and the whole community would flip to breed at the beginning of the rainy season, as Skutch had found in Costa Rica.

In the tropics, the abundance of insects is directly tied to rainfall, a fact that Newell knows firsthand. In a separate analysis of the data she’d collected in Peru, she was again caught off guard when the results showed that tropical insects seem to have a Goldilocks preference for the amount of rainfall. Too little is obviously bad, but too much rainfall can similarly reduce their abundance and biomass.

“Intermediate rainfall is where their biomass is highest,” she said. Similar to tropical birds, little is known about the biology of tropical insects. Newell’s results were the first to show that too much rainfall can be detrimental to their abundance, and even now, the functional relationship between the two remains unclear.

This leaves both insects and the animals that eat them especially susceptible to global climate change. Long-term studies have documented declines in many tropical bird species, especially insectivores, and changes in insect biomass could explain some of these declines.

The team’s work has also shown deforestation in the Andes Mountains has jeopardized the existence of hundreds of birds that are specially adapted to the green-tinted gloom created by densely packed tropical trees.  

The authors published their study in the journal Global Change Biology.

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Journal

Global Change Biology

DOI

10.1111/gcb.70790 

Article Title

Changing Rainfall Drives Locally Asynchronous Reproduction of Tropical Birds via Modular Trophic Pathways

Article Publication Date

26-Mar-2026