Migratory birds find their wintering spot in Africa thanks to an interplay between genes and environment
image:
Pied Flycatcher male with a light-level geolocator on its back, which had its migration tracked from the Dutch population, Aekingerzand, The Netherlands, 9 June 2027. Credits Richard Ubels
view moreCredit: Richard Ubels, University of Groningen
Migratory birds such as the pied flycatcher typically have wintering locations in Africa close to others from the same breeding population. That means that birds breeding in the Netherlands run into each other again in Afrika, while, for instance, Spanish populations also end up close together. But how do they know where to go? A team of European researchers tracked the migration of pied flycatchers from eight different countries, but also performed a crucial intervention: what happens to the birds of Dutch eggs that are being raised by Swedish foster parents? The results of this study appeared in Science on June 25, and the researchers conclude that genes as well as environment influence where in Africa a bird finds its wintering spot.
Every fall, billions of migratory birds leave their breeding areas to go to a wintering location elsewhere. The pied flycatcher, a small bird of just 12 grams, travels some 3000 to 13,000 kilometres to Afrika. There, he often settles in a place where also his peers from the same population reside: pied flycatchers from the Netherlands run into each other in Africa in winter, while their Spanish counterparts meet up elsewhere in Africa.
Why birds from a certain breeding area migrate to such a specific wintering location, is not yet understood. For some species of birds, it’s obvious: young geese learn from their parents, and several other species learn from their travel companions. But for song birds that travel alone and in the night, it is not yet clear why the end up at a specific spot.
A non-stop flight of some forty hours
A large team of European researchers studied the pied flycatcher’s migration from eight different locations in the entire breeding area. The project was coordinated by Koosje Lamers and Janne Ouwehand from the University of Groningen (UG), under supervision of Christiaan Both (also UG). From Spain to Siberia, flycatchers were tracked using dataloggers to record their route to west-Africa. All populations first flew to Spain and Portugal in fall. There, they stopped for some time, before embarking on a non-stop flight of about forty hours over the Atlantic to the most western part of Africa.
After that, their migration route bent eastward, and the birds flew various distances: Spanish birds resided in the most western part of the wintering locations, while the Siberians went farther east to spend their winter in Nigeria. While the Spanish breeding population only flew about 3000 kilometres in fall, the Siberians travelled almost 13,000 kilometres because of the long detour via Spain and Portugal.
‘It is remarkable that these pied flycatchers from Siberia take such a detour,’ remarks PhD-student Koosje Lamers. ‘A less western route, for instance, crossing the Mediterranean Sea near Italy and then crossing the Sahara, would save them some 4,500 kilometres.’ This shorter route is in fact a perfectly fine alternative, because the collared flycatcher, which is closely related, uses it to fly from Central Europe to their African wintering locations. Lamers: ‘So it is plausible that this strange detour is an evolutionary remnant from the past, when during ice ages, the pied flycatchers only appeared in the western part of Africa and Europe.’
Raised by Swedish foster parents
To determine how pied flycatchers know where to go in Africa for wintering, the researchers translocated flycatchers from The Netherlands to South-Sweden. They did this by removing Dutch eggs, and having them hatched out and raised by Swedish parents. They also moved female Dutch birds to Sweden, resulting in half-Dutch-half-Swedish offspring. The migration routes from the Dutch and Swedish populations where then tracked. Lamers: ’The non-translocated Dutch flycatchers turned out to end up some 500 kilometres more to the east in West-Africa than Swedish counterparts. And Dutch flycatchers that grew up in Sweden, went to a location about halfway between the normal Dutch and Swedish locations, and the mixed offspring was a bit closer to the normal Swedish locations in Africa.’
This study shows that the wintering location of flycatchers is determined by a mixture of inheritance and natal environment. In addition, it is remarkable that the population-specific wintering locations are reached via shared routes. Lamers: ‘So, it is probably not the case that the direction of the migration is inherited, and differs per location. Instead, it is probably the length of the route that is fixed.’
Finally, the study shows that this migration behaviour is not learned from the parents, because their young embark on their travels later in the year. This knowledge is relevant to understand how migratory birds might adapt to climate change. The timing of their migration is heavily influenced by climate change, and whether or not the birds can start earlier, depends on where in Africa they spend their winter. Lamers: ‘Moreover, our research shows that new combinations of breeding areas and wintering locations can arise, as we saw with the Dutch eggs that hatched in Sweden.’
Juvenile Pied Flycatcher a few days after fledging. They are still fed by their parents and in about one and a half month they will departure to the wintering grounds, Aekingerzand, The Netherlands, 12 June 2017. Credits Richard Ubels
Credit
Richard Ubels, University of Groningen
Pied Flycatcher on its wintering grounds in Ivory Coast. Credits Sander Bot
Credit
Sander Bot, University of Groningen
Dutch pied flycatcher eggs collected for translocation to Sweden. Credit: Koosje Lamers
Credit
Koosje Lamers, University of Groningen
Pied Flycatcher male of Dutch descent in Sweden. This male hatched from a Dutch egg translocated to Sweden in the experiment, returned the next year as an adult, and was then deployed with a datalogger on its back to track its migration. The aluminum ring and a small yellow color ring (for visual recognition) are visible. Credits Koosje Lamers
Credit
Koosje Lamers, University of Groningen
Journal
Science
Method of Research
Experimental study
Article Title
Innate factors and ontogeny determine non-breeding areas of migrant songbirds
Tiny raptor, tiny range: GPS tracking reveals Pygmy Falcons use less than 1 km² to raise nestlings
University of Cape Town - Faculty of Science
image:
A breeding pair of Pygmy Falcon
view moreCredit: Olufemi Olubodun
A new study, published in the Journal of Raptor Research revealed that Africa’s smallest diurnal bird of prey, the Pygmy Falcon (Polihierax semitorquatus), operates within one of the smallest breeding home ranges ever recorded for a raptor. The study was led by researchers from the University of Cape Town with collaborators at Hartpury University, and the Forest Science and Technology Centre of Catalonia. Using ultra-light GPS tracking technology, researchers found that these birds require less than 1 km² to raise their young, challenging long-held assumptions regarding the spatial needs of predatory birds.
A defining characteristic of the Pygmy Falcon’s ecology is its unusual nesting strategy. Unlike most raptors that construct their own nests, the Pygmy Falcon depends entirely on the nests constructed by the Sociable Weaver (Philetairus socius). They roost and breed in chambers within the massive, multi-generational communal haystack nest, coexisting with the weavers at these nests, and effectively anchoring their activities around a weaver colony.
To capture this fine-scale movement, the research team deployed miniaturized GPS tags weighing less than two grams—manufactured by Pathtrack Ltd—on 13 adult Pygmy Falcons at Tswalu Kalahari, a private reserve in South Africa. Because the falcons weigh only about 56 grams, such studies were historically impossible until recent breakthroughs in technology.
The data, comprising nearly 4,000 GPS locations, showed that during the chick-rearing phase, the falcons utilized an average area of just 0.93 km². This is approximately 14 times smaller than the home range of the Lesser Kestrel, previously one of the smallest GPS-tracked raptors.
The findings suggest that conservation strategies modelled after wide-ranging "umbrella species," such as eagles or vultures, may not fully capture the ecological requirements of smaller predators. “This study provides a crucial baseline for understanding the spatial requirements of small raptors, which have been largely overlooked due to technological limitations,” said lead author Dr. Olufemi Olubodun, Carnegie Postdoctoral Fellow at the FitzPatrick Institute of African Ornithology (Fitz). “While wide-ranging raptors are often used as surrogates for broad-scale conservation plans, species with smaller home ranges may complement this role by reflecting ecological processes operating at finer spatial scales.”
The study also revealed a surprising lack of sexual dimorphism in movement. While female raptors are typically larger and often exhibit different movement patterns than males, both male and female Pygmy Falcons used similar-sized home ranges. This suggests “a high degree of shared parental responsibility during the critical period of chick-rearing”, said senior author Associate Professor Robert Thomson also from the Fitz. “Small raptors have been underrepresented in movement ecology, now with advances in technology, we can begin to understand their ecology in the same detail as larger species.”
The researchers note that while these findings are definitive for the breeding season, further study is required to determine how these home ranges shift during the non-breeding months when the birds are not tethered to the weaver colonies for raising nestlings.
Journal
Journal of Raptor Research
Method of Research
Observational study
Subject of Research
Animals
Article Title
Breeding Home Range of the Pygmy Falcon: The Smallest GPS-Tracked Diurnal Raptor
A female Pygmy Falcon perches beneath a Sociable Weaver colony, prey clasped in her beak, moments before entering into one of the colony's chambers to provision its nestlings.
Credit
Anthony Lowney
Article Publication Date
25-Jun-2026
What molting hawks can teach researchers about resilient flight
Red-tailed hawks maintain flight performance despite missing feathers
image:
Jack, a red-tailed hawk, alights on a perch. Research shows that the birds can compensate for feather loss during molt by changing their wing and tail movements.
view moreCredit: Alfonso MartÃnez-Carmena, UC Davis
Red-tailed hawks can compensate for feather loss during molt by subtly changing their wing and tail movements, according to a new study by University of California, Davis, researchers in the College of Engineering and the Weill School of Veterinary Medicine.
The findings could inform wildlife rehabilitation efforts for birds of prey and inspire the design of more resilient uncrewed aerial vehicles, or UAVs, that can continue operating despite losing part of a wing or control surface.
The study was published June 17 in The Royal Society Publishing.
“We see during molt that the bird experiences a temporary reduction in aerodynamic capability due to the missing feathers but still maintains performance by adjusting the kinematics,” said Alfonso MartÃnez-Carmena, lead author on the paper and a postdoctoral researcher in the Department of Mechanical and Aerospace Engineering. “For UAV design, this could translate into morphing structures or adaptive flight controllers that can compensate for changes in the aerodynamic configuration, such as damage or component degradation, rather than relying on a fixed optimal design.”
During molt, which typically occurs at least once a year, birds shed old feathers to make room for new ones. The process leaves gaps in the wings and tail, which can make flight more difficult. Yet birds still need to fly to navigate their environment, hunt and perch.
Using four synchronized high-speed cameras, MartÃnez-Carmena tracked wing and tail movements of Jack, a resident red-tailed hawk at the California Raptor Center, a rehabilitation center for birds of prey at the Weill School of Veterinary Medicine. While Jack flew from a handler’s arm to a fixed perch, the handler moved their arm between heights for each flight.
This maneuver, said MartÃnez-Carmena, involves intense coordination.
“It requires the bird to fly at low speed, with its wings operating at high angles of attack, a regime in which aerodynamic forces become nonlinear and difficult to predict,” he said. “It necessitates continuous adjustment of the body, the wing and the tail kinematics to balance forces right up to touchdown.”
The hawk was filmed performing this maneuver during natural molt and again after its feathers had fully regrown. The researchers found that during molt, several tail feathers were missing, reducing the hawk’s tail area. The bird compensated for this by changing its tail angle immediately after takeoff, which may have contributed to the additional transient thrust observed by MartÃnez-Carmena.
The hawk also adjusted its wing motion, putting its wings closer together during part of each wingbeat, potentially helping reduce gaps caused by missing feathers. Overall, the hawk maintained flight performance despite having fewer feathers.
Researchers plan to extend the study to additional bird species and across the entire molting season to investigate how kinematic variations change depending on the location of feather gaps in the tail and wings.
This study is the first to emerge from the interdisciplinary partnership between Assistant Professor of Mechanical and Aerospace Engineering Christina Harvey and Michelle Hawkins, a professor of veterinary medicine and director of the California Raptor Center. Their partnership is now formalized as the Center for Animal Locomotion and Innovation.
Journal
Journal of The Royal Society Interface
Subject of Research
Animals
Article Title
Tuning for feather loss: wing–tail kinematic adjustments of a moulting red-tailed hawk during perching flight
Article Publication Date
27-Jun-2026
Animation of hawk in flight and measurements [VIDEO]
Alfonso MartÃnez-Carmena, a postdoctoral researcher in the Department of Mechanical and Aerospace Engineering, poses with Jack, a red-tailed hawk.
Credit
Courtesy Alfonso MartÃnez-Carmena, UC Davis
