According to Gram Research analysis, Chinese crested terns and greater crested terns eat almost exclusively small schooling fish, with anchovies making up 73% of their diet and mackerel-family fish comprising 27%, according to a 2026 DNA study of 50 birds. These endangered seabirds rarely eat commercially valuable fish, meaning they don’t directly compete with fishing industries for food resources.
Scientists studied what two types of terns eat by analyzing their droppings on breeding islands in China. Using advanced DNA technology, researchers found that these seabirds almost exclusively eat small schooling fish like anchovies, not the commercial fish that humans catch. The study shows these birds don’t compete much with fishing industries for food. However, researchers discovered some terns are eating freshwater fish, suggesting they’re adapting to human-changed environments. These findings are crucial for protecting the critically endangered Chinese crested tern by ensuring their main food sources stay available.
Key Statistics
A 2026 DNA metabarcoding study of 50 terns on Chinese breeding islands found that anchovies and related fish (family Engraulidae) comprised 72.73% of their diet, with mackerel-family fish making up 27.27%.
In the first documented detection of freshwater fish in tern diets in this region, 6.82% of samples (3 out of 44) contained freshwater fish DNA, suggesting behavioral adaptation to human-modified coastal environments.
A 2026 analysis of 50 tern fecal samples revealed that commercially valuable fish species made up less than 5% of the birds’ diet, indicating minimal competition with human fishing industries.
Terns feeding nestlings showed significantly greater dietary diversity (higher Chao index) compared to birds in pre-breeding stages, demonstrating increased foraging flexibility during the provisioning period.
The Quick Take
- What they studied: What do Chinese crested terns and greater crested terns eat during breeding season, and how does their diet change as they raise their babies?
- Who participated: Researchers collected droppings from 50 terns across two breeding islands in Zhejiang, China, studying both adult birds and those raising nestlings.
- Key finding: Both tern species eat almost the same diet: about 73% anchovies and related small fish, with 27% being mackerel-family fish. They rarely eat commercially valuable fish that humans catch.
- What it means for you: These endangered birds don’t directly compete with fishing industries for food, which means fishing regulations don’t need to protect the same fish species. However, protecting the small fish these terns depend on is critical for their survival.
The Research Details
Researchers collected poop samples from 50 terns on two Chinese breeding islands during the 2024 breeding season. They analyzed the DNA in these samples using a technique called DNA metabarcoding, which identifies what fish species the birds ate by reading the genetic material left in their droppings. This method is like reading a receipt that shows exactly what the bird had for dinner.
The team examined samples during two time periods: when birds were preparing to breed and when they were actively feeding baby birds. They used two different genetic markers (12S and COI regions) to make sure they correctly identified every fish species. This double-checking approach increases confidence in the results.
By comparing their findings with similar studies from Australia and South Africa, the researchers could see if terns worldwide eat the same foods or if their diets vary by location.
This research approach is important because it reveals exactly what endangered birds eat without disturbing them or needing to watch them constantly. Understanding diet is essential for conservation because it shows what resources these birds need to survive and reproduce. If we know what they eat, we can protect those specific fish populations and understand how human activities like fishing might affect the birds.
This study has several strengths: it used advanced DNA technology that accurately identifies fish species, it examined samples from two different islands to check consistency, and it compared results with international research. The sample size of 50 is reasonable for this type of study. One limitation is that the study only covered one breeding season, so researchers couldn’t determine if diet varies year to year. The study also relied on fecal samples, which show what birds ate recently but not their complete diet over time.
What the Results Show
The DNA analysis revealed that both tern species have a highly specialized diet focused on small schooling fish. Anchovies and their relatives (family Engraulidae) made up 72.73% of their diet, while mackerel-family fish (Scombridae) comprised 27.27%. The three most important fish species were Japanese anchovy, slender silverside, and kammal thryssa.
When researchers compared diets between breeding stages, they found something interesting: adult birds feeding nestlings showed more dietary variety than birds preparing to breed. This suggests that when terns need to feed hungry babies, they become more flexible about what fish they catch, eating a wider range of species.
Comparing the two islands and different breeding stages, the overall pattern of fish families remained consistent. However, at the species level—looking at specific types of fish—the diet changed noticeably between breeding stages, showing these birds can adapt their hunting strategy based on circumstances.
A surprising finding was that 6.82% of samples (3 out of 44) contained freshwater fish DNA. This is the first time freshwater fish have been documented in tern diets in this region, suggesting these birds are adapting to human-modified environments where freshwater and marine habitats mix.
The study found that commercially valuable fish species made up less than 5% of the terns’ diet, indicating minimal competition with human fishing industries. This is important because it suggests fishing regulations don’t need to restrict the same species that terns depend on. The presence of freshwater fish in some samples highlights behavioral flexibility—these birds are learning to hunt in new environments created by human development. The greater dietary diversity during the nestling-feeding stage (measured by a statistical measure called the Chao index) shows that terns adjust their foraging strategy when they have more mouths to feed.
This research aligns with studies from Australia and South Africa showing that greater crested terns worldwide specialize in epipelagic schooling fish (fish that swim near the ocean surface in groups). The findings support the idea that this is a universal characteristic of the species globally. The discovery of freshwater fish in tern diets is novel for this region and suggests that as human activities modify coastal environments, these birds are developing new feeding behaviors not previously documented.
The study examined only 50 samples from one breeding season, so researchers cannot determine if diet varies significantly from year to year or if these patterns hold during non-breeding seasons. The research focused on two specific islands, so results may not apply to tern populations in other regions. DNA metabarcoding can identify what fish were eaten but cannot determine how much of each species was consumed by weight. Additionally, the study couldn’t determine whether the freshwater fish findings represent a new adaptation or an occasional occurrence, since only three samples contained freshwater fish DNA.
The Bottom Line
Based on this research, conservation efforts should prioritize protecting anchovy and related small fish populations in coastal waters where these terns breed. Fishing regulations should be designed to maintain healthy populations of these species. Coastal development should be managed to prevent further habitat modification that might force terns into human-altered environments. These recommendations have strong evidence support from this study combined with international research.
Fisheries managers, conservation organizations, and government agencies responsible for protecting endangered species should use these findings. Policymakers in coastal regions where these terns breed need this information to balance fishing interests with bird conservation. The general public should care because protecting these seabirds indicates healthy ocean ecosystems that benefit all marine life, including fish populations humans depend on.
Protecting fish populations takes time. If conservation measures are implemented now, tern breeding success could improve within 2-3 breeding seasons as food availability stabilizes. However, rebuilding depleted fish populations may take 5-10 years depending on fishing pressure and ocean conditions.
Frequently Asked Questions
What fish do endangered Chinese crested terns eat?
Chinese crested terns primarily eat small schooling fish, especially anchovies (73% of diet) and mackerel-family fish (27%), according to a 2026 DNA study of 50 birds. The three key species are Japanese anchovy, slender silverside, and kammal thryssa.
Do terns compete with fishing industries for fish?
No, terns show minimal competition with commercial fishing. A 2026 study found commercially valuable fish comprised less than 5% of tern diets, indicating niche separation from human fisheries targeting the same waters.
How does tern diet change during breeding season?
Terns feeding nestlings eat more diverse fish species than birds in pre-breeding stages, showing greater foraging flexibility when provisioning hungry chicks. The overall fish families remain consistent, but specific species choices vary significantly.
Why is protecting small fish important for tern conservation?
Since anchovies and related schooling fish comprise over 70% of tern diet, maintaining healthy populations of these species is essential for breeding success. Protecting these prey resources directly supports recovery of the critically endangered Chinese crested tern.
Are terns eating new types of fish due to human activity?
Yes, freshwater fish appeared in 6.82% of samples—the first documented occurrence in this region. This suggests terns are adapting to human-modified coastal environments where freshwater and marine habitats mix, indicating behavioral plasticity.
Want to Apply This Research?
- Users interested in seabird conservation could track local fish population health by recording anchovy catch data or participating in citizen science programs that monitor small fish abundance in coastal waters.
- Users could support conservation by choosing seafood products certified as sustainable, particularly avoiding overfishing of small schooling fish species that endangered terns depend on. They could also support marine protected areas that preserve tern breeding habitats.
- Long-term tracking could involve monitoring tern breeding success rates in your region, participating in seabird surveys, or tracking changes in local fish populations through community science initiatives. Users could set reminders to check annual tern breeding reports from conservation organizations.
This research describes the diet of specific tern species and has no direct application to human health or medical treatment. The findings are based on a single breeding season study of 50 birds from two islands in China and may not apply to all tern populations globally. Conservation decisions should be made in consultation with wildlife biologists and fisheries experts. This article is for informational purposes and should not be used as the sole basis for environmental policy decisions.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.