A field experiment on wild kittiwakes in Alaska reveals how short-term energy demands ripple across the year, with consequences for future reproduction and survival.

 
Wild seabirds that face high energy demands during the breeding season go on to migrate farther and raise more chicks the next year, but at a cost to their own survival. An international team, led by researchers from ºÚÁϳԹÏÍø, raised the energy cost of flight for some birds and tracked them through the next year of their annual cycle. The researchers introduce a concept called “energetic flexibility” and offer rare experimental evidence for how the costs of one season carry over to shape the next. The study appears in . 
 
The team studied 251 black-legged kittiwakes on Middleton Island, Alaska, from 2021 to 2024. In 2021, they altered the energy cost of breeding for three groups. One group received extra food, which reduced the energy cost of raising chicks. For a second group, the team clipped three wing feathers and two tail feathers at the base shortly after the birds had laid their eggs. This raised the energy cost of flight for the rest of the breeding season. The feathers grew back at the birds’ next molt. A third group was left alone as a control. 
 
Each bird carried a geolocator that recorded its movements through the non-breeding season. The team recovered 203 of the 251 devices the next year and tracked the same individuals through 2024. 
 
Birds with raised energy costs fledged only 10% of their chicks that year. The fed group and the control group did much better: 44% and 43% respectively. The high-cost birds also departed about 10 days earlier than the other groups, leaving the colony at the end of the breeding season to head out to sea for the long migration across the North Pacific Ocean. ? 

¡°Earlier departure from the breeding colony by birds that failed to raise chicks has long been recognized. However, our study demonstrates that early departure is driven not by breeding success or failure itself, but by the energetic costs incurred during reproduction,¡± said Akiko Shoji, senior author and professor at the , ºÚÁϳԹÏÍø. In other words, breeding failure appears to be one consequence of high energetic costs, rather than the direct cause of early departure.¡± 
 
Their earlier departure also resulted in longer migrations. Birds that travelled farther during the non-breeding season were more likely to breed successfully the following year. This suggests that longer migrations may facilitate recovery from the energetic costs incurred during breeding. 
 
However, they paid a price in survival. Only 67% of the high-cost birds returned the next year, compared with 83% of the control group and 90% of the fed group. 
 
The researchers say this pattern points to a hidden trade-off. To recover from a hard breeding season, kittiwakes invested more in the next migration. That strategy paid off in future reproduction but also lowered their chances of survival.  

While the survival cost of high energy demands during breeding has been documented in seabirds before, this study is the first to experimentally show that the same birds also gain more chicks the following year, through changes in their migration. ? 

¡°We use the term ‘energetic flexibility’ to describe an animal’s ability to flexibly adjust energy allocation among reproduction, survival, and migration as environmental conditions change. Our study suggests that this flexibility may be a key mechanism underlying carry-over effects, helping to explain how events in one season influence reproduction and survival in the next,¡± Shoji said. 

The findings have implications for seabirds as climate change reshapes the oceans. As prey availability shifts and conditions become less predictable, the ability to reallocate energy across seasons may decide which populations cope and which decline.?
?
The team plans to use miniature heart-rate loggers to track kittiwakes’ energy use throughout the year and identify the biological processes that drive this flexibility.?

Paper information:?

Chinatsu Nakajima, Don-Jean L¨¦andri-Breton, Marie Claire Gatt, Joan Ferrer Obiol, Diego Rubolini, Jacopo G. Cecere, Kyle H. Elliott, Shannon Whelan, Scott A. Hatch, Yasuaki Niizuma, Ken-ichiro Minato, Shigeki Wada and Akiko Shoji. 2026. Energetic flexibility as a hidden axis of life-history trade-offs: experimental evidence from a long-lived seabird, Proceedings of the Royal Society B, 293: 20253274. DOI:

Funding information:  

This work was supported by Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (19KK0159, 20H04374, 22K21355, 23KK0116) and by the Projects of Relevant National Interest 2017 funding scheme from the Italian Ministry of University and Research (20178T2PSW). 

Expert contact:  

Akiko Shoji
Graduate School of Environmental Studies
ºÚÁϳԹÏÍø?
Email: akiko.shoji@nagoya-u.jp

Media contact:  

Merle Naidoo
International Communications Office
ºÚÁϳԹÏÍø
Email: icomm_research@t.mail.nagoya-u.ac.jp?

Top image:

Adult black-legged kittiwakes tend to their chicks at a breeding colony on Middleton Island, Alaska, where researchers experimentally raised the energy cost of flight in some birds during breeding. The study shows that birds paying higher energy costs to raise chicks migrate farther and breed more successfully the next year, but at a cost to their survival. Credit: Jumpei Okado, ºÚÁϳԹÏÍø  
 

Scientists use clues from inhabitants and ocean current simulations to show how a small piece of plastic waste can transport a micro-ecosystem to new regions

Researchers have traced the journey of a plastic bottle cap recovered near the waters of southern Japan by combining data from the label, chemical clues in tiny shells, and ocean current simulations. They found 307 organisms, including a polychaetae worm not found in Japanese waters before. The findings, published in , show that when species that significantly shape their environments (ecosystem engineers) colonize plastic debris, entire micro-communities can be transported over extended periods, with implications for invasive species risk and marine biodiversity conservation. 

Marine plastic waste poses direct threats such as ingestion and entanglement but can also transport attached organisms to distant locations. Plastic can remain at the sea surface longer than natural drifting materials such as wood or seaweed. Consequently, marine plastics represent a growing pathway for dispersing organisms to new regions. 

This is the first study to combine information from the organisms attached, chemical records of past environmental conditions preserved in shells, and ocean current simulations to trace a single small piece of ocean plastic. ? 

Bottle cap habitat engineered by a worm 

Nine taxonomic groups and 307 individuals were found, including tiny tube-building worms, bryozoans (tiny colonial filter-feeders), gooseneck barnacles, foraminifera, flatworms, and larger polychaete worm species. ºÚÁϳԹÏÍø three-quarters of the individuals were tiny worms that build coiled calcareous tubes.  

“The most striking colonist was a polychaete worm, Eunice bipapillata, which had built a nest that transformed the cap into a complex three-dimensional habitat. Inside, we found organisms that normally live in southern tropical waters,” said Naoto Jimi, lead author and lecturer at ºÚÁϳԹÏÍø’s . “Geographic range extensions of some species may be occurring under the radar, so if this waste can be properly disposed, we may reduce the number of non-native species carried into new habitats.”

Evidence to trace the origins and drift route 

The researchers investigated where the cap originated, the water temperatures it had passed through, and whether those temperatures matched the sea surface temperatures along drift paths predicted by ocean current simulations. Three sources of evidence were used: 

1. Biofouling community: The coexistence of coastal seafloor and reef species as well as typical open-ocean foulers (organisms that attach to floating objects in the ocean) suggested that the cap had passed through both coastal and open-ocean environments. 

2. Foraminiferal stable isotopes: Foraminifera, single-celled organisms that build intricate shells, record ambient water temperature as they grow their shells. Stable isotope analysis measures the ratios of isotopes of an element to obtain clues about the environment an organism has experienced. Analysis of different parts of the shells suggested that the specimens had experienced warmer waters before reaching the collection site, where the water temperature was about 22 degrees Celsius. 

3. Ocean current modeling: Using surface drift current simulations, virtual particles were released into ocean current models to reproduce possible drift paths of debris. They indicated that the cap likely drifted from the northern Philippines on the Kuroshio system and reached the collection area in at least 70 days and up to several months.

Small plastics, big consequences

This study shows that when ecosystem engineers such as tube-building worms colonize small plastic fragments, these plastics may serve as shelters and transport vehicles that allow multiple organisms to survive together. This may result in entire biological communities reaching new regions.  

¡°The marine plastic problem should therefore be considered not only from the perspectives of aesthetic damage, ingestion, and entanglement, but also from those of biogeography and invasive species risk,¡± said Jimi. ¡°Multi-method reconstructions of the drift history of marine debris may support future estimation and control of invasive species pathways originating from ocean waste.¡± 

The researchers conclude that future research should quantify how frequently small plastics host organisms found at the bottom of marine habitats, identify which taxa are most likely to survive during drift, and evaluate ecological outcomes if debris-borne organisms arrive and establish in new environments. 

Publication information: 

Naoto Jimi, Naoki Saito, Akito Ogawa, Hiroki Kise, Natsumi Hookabe, Toyoho Ishimura, Masashi Tsuchiya, 2026. Multi-proxy reconstruction of bottle-cap rafting using biofouling communities, stable isotopes and drift modeling, Marine Pollution Bulletin, 232,120051. DOI:

Funding information:

This research was supported by the Narishige Zoological Science Award and JSPS KAKENHI (22K15165). 

Expert contact: 

Naoto Jimi  
Sugashima Marine Biological Laboratory 
ºÚÁϳԹÏÍø 
Email: jimi.naoto.p0@f.mail.nagoya-u.ac.jp 

Media contact: 

Merle Naidoo
International Communications Office
ºÚÁϳԹÏÍø
Email: icomm_research@t.mail.nagoya-u.ac.jp 

Top image:

Inside a 3.5 cm plastic bottle cap: A miniature ecosystem of 307 organisms drifted from the Philippines to waters south of Japan. Credit: Sugashima Marine Biological Laboratory, ºÚÁϳԹÏÍø

The analysis was based on blood samples from over 11,000 seabirds, the first biologically derived estimate of oceanic mercury distribution.

Mercury released into the oceans affects marine environments worldwide. Traditionally, its distribution and quantity have been estimated using marine biogeochemical simulation models.

A recent international study led by Japanese researchers analyzed blood mercury concentrations in more than 11,215 seabirds from 108 species, of which 659 were newly collected samples and over 10,556 were from previous studies. This is the first biologically based estimate of oceanic mercury distribution.

The study found that mercury levels in seabirds vary according to prey trophic level, bird body weight, and foraging depth. The findings were published in .

Mercury emissions into the ocean have risen since the Industrial Revolution, primarily due to increased atmospheric mercury from coal combustion. Mercury travels long distances by wind and enters the ocean through rainfall.

In the ocean, some mercury becomes highly toxic and bioaccumulates in the food chain, ultimately concentrating in the tissues of seabirds that consume fish and zooplankton.

Professor and Researcher Jumpei Okado of , along with Senior Researcher Bungo Nishizawa of the Japan Fisheries Research and Education Agency, led an international study with 12 institutions from four countries.

Why were seabird blood samples used?

Blood samples from seabirds are efficiently collected when they come ashore for breeding. Mercury concentrations in adult birds’ blood at breeding sites reflect their dietary mercury intake from specific ocean areas within the two months prior to sampling.

This method enables a more accurate correlation of mercury levels with specific times and locations than other sample types. Additionally, blood collection causes minimal harm to the birds.

Analysis of seabird blood data

Between 2017 and 2024, researchers collected blood samples from 659 individuals representing 10 seabird species at breeding sites in Japan, Alaska, and New Zealand. They dried and homogenized the samples, then measured total mercury concentrations using atomic absorption spectrometry. Results were standardized to total mercury per gram of dry weight in whole blood for comparison.

Researchers also conducted a systematic review of 106 publications from 1980 to 2025, with over 80% published after 2010, and analyzed data on more than 10,556 adults representing 105 seabird species.

In total, the team analyzed blood mercury concentrations in over 11,215 individuals from 108 seabird species worldwide, covering diverse diets and geographic regions.

The analysis found that seabirds at higher trophic levels, with larger body mass, and those feeding on prey from depths between 200 and 1,000 meters have higher mercury levels.

Statistical analysis showed distinct regional patterns in oceanic mercury contamination. Mercury levels were higher in the North Atlantic, North Pacific, South Pacific below 40 degrees south, and in areas with low productivity, as indicated by reduced chlorophyll a levels. In contrast, mercury levels were much lower in the South Atlantic and Southern Oceans.

The study also found that albatrosses and shearwaters are more exposed to mercury than other seabird species.

Significance and future perspectives

The researchers found that predictions from the seabird-based model and the marine biogeochemical simulation models were only weakly correlated.

“The seabird model is based on empirical measurements from organisms and is therefore considered more reliable than values from marine simulation models,” said Shoji. “Seabirds live in diverse environments, from coastal and tropical zones to polar regions. Their varied feeding patterns make them effective indicators of global ocean health.” ?

This approach offers a promising method to monitor and verify the effectiveness of international mercury emission regulations, such as the Minamata Convention, and to support stronger global efforts to reduce mercury contamination in marine ecosystems.

Paper information

Jumpei Okado, Bungo Nishizawa, Johannes H. Fischer, Olivia C. Rowley, Yukihiko Toquenaga, Yasuaki Niizuma, Chinatsu Nakajima, Futoshi Ujiie, Toru Kawai, Shannon Whelan, Scott A. Hatch, Paco Bustamante, Graeme Elliott, Graham C. Parker, Kalinka Rexer-Huber, Kate Simister, Grace Tocker, Kath Walker, Heiko U. Wittmer, Igor Debski, Akiko Shoji (2026). Global drivers of variation in blood mercury of seabirds revealed by a meta-analysis, Science of The Total Environment.

Funding information

This study was supported by the Japan Society for the Promotion of Science (Grants-in-Aid for Scientific Research awarded to AS: 23KK0116, 22K21355, and 19KK0159), Japan Science and Technology Agency (EXPLORATORY RESEARCH GRANT awarded to AS: JPMJFR241E), and Japan Polar Research Association (2022 and 2023 awarded to CN). Sample collection in Aotearoa New Zealand was supported by the Conservation Services Programme of the Department of Conservation (POP2022¨C08, POP20220¨C7, and POP2022¨C10), the National Geographic Society (WW-249C-17), the Mohamed Bin Zayed Species Conservation Fund (Project 192520234), and Birds New Zealand (Birds NZ Research fund 2017, 2019).

Expert contact:

Akiko Shoji
Graduate School of Environmental Studies, ºÚÁϳԹÏÍø
Email: akiko.shoji@nagoya-u.jp

Media contact:

Naomi Inoue
International Communications Office, ºÚÁϳԹÏÍø
Email: icomm_research@t.mail.nagoya-u.ac.jp

Top image:

This study provides the drivers of variation in mercury concentrations in seabirds and, further, the first biologically based estimate of oceanic mercury distribution, analyzing blood mercury levels in more than 11,215 seabirds from 108 species, including 659 newly collected samples and over 10,556 from prior research. (THg: total mercury)
Credit: Jumpei Okado (modified from Okado et al. 2026, licensed under CC BY 4.0)

It will be held on March 18, 2026 (10:00 AM – 12:00 PM at) ºÚÁϳԹÏÍø, Environmental Studies Building, 1F Lecture Hall, and via Zoom.

Please find the attached promotional material while the registration link and the zoom details are as follows:

Topic: Nagoya-Philippines Watershed Workshop
Time: 18 March 2026, 10:00 AM (Osaka, Sapporo, Tokyo)