Increased energetic cost of migration due to fewer stopovers and longer distances could result in a higher mortality rate than natural causes, notes study
The ongoing war between Russia and Ukraine has forced greater spotted eagles to change their migratory paths, making their journey more arduous and causing them to skip much-needed stopovers.
The conflict, which began in February 2022, coincided with the species’ migration period in March-April.
A study, Active European Warzone Impacts Raptor Migration, published in journal Current Biology, tracked the movements of 19 eagles tagged for another study. The researchers observed changes in their behaviour due to the war.
Researchers from the University of East Anglia, the British Trust for Ornithology and local partners in Estonia and Belarus had been tracking the eagles’ movements from wetlands in eastern Africa to 5,000 kilometres in Europe since 2017 to identify conservation areas and assist in recovering the depleting populations.
The Greater Spotted Eagle, a large raptor species, is listed as Vulnerable on the International Union for Conservation of Nature (IUCN) Red List. The species has mostly vanished from western and central Europe, with a limited breeding population in Polesia, Belarus.
The deviation in their path and the curtailment of stopovers have resulted in delays in arriving at breeding grounds, making the journey more energy-demanding with “sublethal” fitness effects.
The study’s lead author Charlie Russell, a PhD student at the University of East Anglia, described the species’ problems in an article published on the website of a non-profit conservation network, The Wildlife Society.
“In the most extreme cases, it’s like if you were running a marathon but you’re not allowed to take any water breaks,” Russell said, “and at the end someone makes you run an extra eight miles. It’s crazy to think about.”
Among the 18 eagles tracked, 15 significantly changed their paths, increasing their 800 km journey across Ukraine by over 80 km. One eagle logged an additional 250 km. The study observed that eagles reduced their much-needed stopovers by 60 per cent, which are crucial for recovery, feeding and completing their migration.
Contrary to earlier observations, the researchers found that about 90 per cent of the eagles used Ukraine as a stopover between 2018 and 2021, but in 2022, only 32 per cent did so.
Responding to an email query, Russell said that, “To our knowledge, this is the first study on how war impacts animal behaviour, as observing these changes in conflict zones is typically not possible. Our dataset provides a unique window into this.”
The researchers also found that the eagles migrated more slowly and flew higher than usual during their journey.
“Artillery fire and jets, tanks and other weaponry increased potential disturbance to wildlife, including the Greater Spotted Eagles in Ukraine, with unprecedented numbers of soldiers moving through the landscape and more than 10 million civilians displaced,” the study noted.
However, the researchers said it is unclear what triggered the responses of the tagged eagles. It may vary from visual or auditory factors of military activities to traffic, light, noise or a combination of these factors that could impact their behaviour.
They noted that the increased energetic cost of migration due to fewer stopovers and longer distances could result in a higher mortality rate than natural causes. Energy expenditures spike, causing immediate stress to these birds.
Speaking about the challenges faced by the raptors, Russell added that migration through Ukraine is at the end of their journey. It is an important area for them to make stopovers and recover their energy, making them vulnerable to threats like habitat loss.
These factors could eventually impact their recovery and improve their body condition for their return journey to breeding grounds, especially for the slow breeding species. The species is considered to have low breeding success with a production of one chick a year.
Russell said, “This is a really important flyway. There are nearly 150 breeding pairs in Polesia, a significant proportion of the European breeding population and most of these birds will be migrating through or breeding in Ukraine. Greater Spotted Eagles raise 1-2 chicks per year and mature slowly, so any impacts on breeding success in this region would contribute to population declines.”
The researchers noted the impacts on the birds are likely temporary but may vary depending on the intensity of the conflict zone.
“Our tagged birds migrated typically through central and western Ukraine, where conflict is now less intense, so the impacts here are likely short term. However, for birds migrating through or resident in eastern Ukraine, such as pairs that breed in Kharkiv, the impacts are likely much greater and ongoing,” he said.
“This study increases our understanding of the impacts of extreme anthropogenic disturbance and conflict on migratory raptors, demonstrating decreased route efficiency and highlighting potential sublethal fitness costs,” the study noted.
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