Risto Juvaste | University of Turku (original) (raw)

Papers by Risto Juvaste

During migratory journeys, birds may become displaced from their normal migratory route. Experime... more During migratory journeys, birds may become displaced from their normal migratory route. Experimental evidence has shown that adult birds can correct for such displacements and return to their goal. However, the nature of the cues used by migratory birds to perform long distance navigation is still debated. In this experiment we subjected adult lesser black-backed gulls migrating from their Finnish/Russian breeding grounds (from > 60°N) to Africa (to < 5°N) to sensory manipulation, to determine the sensory systems required for navigation. We translocated birds westward (1080 km) or eastward (885 km) to simulate natural navigational challenges. When translocated westwards and outside their migratory corridor birds with olfactory nerve section kept a clear directional preference (southerly) but were unable to compensate for the displacement, while intact birds and gulls with the ophthalmic branch of the trigeminal nerve sectioned oriented towards their population-specific migratory corridor. Thus, air-borne olfactory information seems to be important for migrating gulls to navigate successfully in some circumstances.

Being faced with unknown environments is a concomitant challenge of species' range expansions... more Being faced with unknown environments is a concomitant challenge of species' range expansions. Strategies to cope with this challenge include the adaptation to local conditions and a flexibility in resource exploitation. The gulls of the <i>Larus argentatus-fuscus-cachinnans</i> group form a system in which ecological flexibility might have enabled them to expand their range considerably, and to colonize urban environments. However, on a population level both flexibility and local adaptation lead to signatures of differential habitat use in different environments, and these processes are not easily distinguished. Using the lesser black-backed gull (<i>Larus fuscus</i>) as a system, we put both flexibility and local adaptation to a test. We compare habitat use between two spatially separated populations, and use a translocation experiment during which individuals were released into novel environment. The experiment revealed that on a population-level flexibility best explains the differences in habitat use between the two populations. We think that our results suggest that the range expansion and huge success of this species complex could be a result of its broad ecological niche and flexibility in the exploitation of resources. However, this also advises caution when using species distribution models to extrapolate habitat use across space.

Royal Society Open Science, 2017

Being faced with unknown environments is a concomitant challenge of species' range expansions. St... more Being faced with unknown environments is a concomitant challenge of species' range expansions. Strategies to cope with this challenge include the adaptation to local conditions and a flexibility in resource exploitation. The gulls of the Larus argentatus-fuscus-cachinnans group form a system in which ecological flexibility might have enabled them to expand their range considerably, and to colonize urban environments. However, on a population level both flexibility and local adaptation lead to signatures of differential habitat use in different environments, and these processes are not easily distinguished. Using the lesser black-backed gull (Larus fuscus) as a system, we put both flexibility and local adaptation to a

Global Ecology and Conservation, Apr 1, 2017

In contrast to many other gull species, nominate lesser black-backed gulls (Larus fuscus fuscus, ... more In contrast to many other gull species, nominate lesser black-backed gulls (Larus fuscus fuscus, nLBBG) have shown generally decreasing population trends throughout their breeding area in northern and eastern Fennoscandia over the past decades and are now red-listed. Interspecific competition, predation, increased disturbance, organochlorine poisoning and food shortages were suggested as main reasons for the overall decrease. Here we contribute to a better understanding of population declines by comparing foraging movements of satellite tracked adult gulls in three geographical areas of Finland (West, South, and East) that differ in their population trends. Our analysis examines potential differences and preferences in the feeding site behaviour of adult gulls. Our comparison of the three geographical areas showed that nLBBGs preferred feeding at fur farms in West Finland, waste dumps in South Finland, and lakes and fields in East Finland. We found individual gulls of this purportedly generalist species to be highly specialised in their foraging behaviour, particularly those that might be associated with their survival probabilities. We ms 23-Mar-2017

Scientific Reports, Nov 24, 2015

During migratory journeys, birds may become displaced from their normal migratory route. Experime... more During migratory journeys, birds may become displaced from their normal migratory route. Experimental evidence has shown that adult birds can correct for such displacements and return to their goal. However, the nature of the cues used by migratory birds to perform long distance navigation is still debated. In this experiment we subjected adult lesser black-backed gulls migrating from their Finnish/Russian breeding grounds (from >60°N) to Africa (to < 5°N) to sensory manipulation, to determine the sensory systems required for navigation. We translocated birds westward (1080 km) or eastward (885 km) to simulate natural navigational challenges. When translocated westwards and outside their migratory corridor birds with olfactory nerve section kept a clear directional preference (southerly) but were unable to compensate for the displacement, while intact birds and gulls with the ophthalmic branch of the trigeminal nerve sectioned oriented towards their population-specific migratory corridor. Thus, airborne olfactory information seems to be important for migrating gulls to navigate successfully in some circumstances.

Satellite tracking of the migratory pathways of first-year Lesser Black-backed Gulls Larus fuscus... more Satellite tracking of the migratory pathways of first-year Lesser Black-backed Gulls Larus fuscus departing from the breeding grounds of different subspecies. Vogelwelt 128: 141-148. The migratory behaviour of two Lesser Black-backed Gull Larus fuscus subspecies, fuscus and intermedius, was studied using satellite telemetry. To this end, first-year birds were equipped with satellite transmitters and released either at their natal site, or after transferring to a breeding site of the other subspecies. In addition, first-year birds from cross-breeding experiments between the two subspecies (fuscus x intermedius) were also equipped with satellite transmitters. In total, eleven first-year birds were successfully tracked during their initial autumn migration, at least one from each study group. First-year birds from the Danish intermedius subspecies migrated either southwest along the coast of the North Sea or through central Europe to Algeria. By contrast, first-year birds from the Finnish fuscus subspecies migrated on a south-southeastern course towards Ukraine and the Bosporus, Turkey. Only one of the transferred gulls could be tracked long enough to accurately determine the migratory behaviour: this bird from the intermedius subspecies left Finland on a south-southeasterly course towards the Ukraine, where transmission ceased. Thus, this gull resembled the migratory behaviour of the fuscus subspecies. One bird from the cross-breeding experiments wintered in Libya, but the migratory behaviour remained unknown due to the lack of positional data.

PLOS ONE, Feb 13, 2015

The ability to control infections is a key trait for migrants that must be balanced against other... more The ability to control infections is a key trait for migrants that must be balanced against other costly features of the migratory life. In this study we explored the links between migration and disease ecology by examining natural variation in parasite exposure and immunity in several populations of Lesser Black-backed Gulls (Larus fuscus) with different migratory strategies. We found higher activity of natural antibodies in long distance migrants from the nominate subspecies L.f.fuscus. Circulating levels of IgY showed large variation at the population level, while immune parameters associated with antimicrobial activity showed extensive variation at the individual level irrespective of population or migratory strategy. Pathogen prevalence showed large geographical variation. However, the seroprevalence of one of the gull-specific subtypes of avian influenza (H16) was associated to the migratory strategy, with lower prevalence among the long-distance migrants, suggesting that migration may play a role in disease dynamics of certain pathogens at the population level.

Ringing and Migration, 2008

Satellite tracking of the migratory pathways of first-year Lesser Black-backed Gulls Larus fuscus... more Satellite tracking of the migratory pathways of first-year Lesser Black-backed Gulls Larus fuscus departing from the breeding grounds of different subspecies. Vogelwelt 128: 141-148. The migratory behaviour of two Lesser Black-backed Gull Larus fuscus subspecies, fuscus and intermedius, was studied using satellite telemetry. To this end, first-year birds were equipped with satellite transmitters and released either at their natal site, or after transferring to a breeding site of the other subspecies. In addition, first-year birds from cross-breeding experiments between the two subspecies (fuscus x intermedius) were also equipped with satellite transmitters. In total, eleven first-year birds were successfully tracked during their initial autumn migration, at least one from each study group. First-year birds from the Danish intermedius subspecies migrated either southwest along the coast of the North Sea or through central Europe to Algeria. By contrast, first-year birds from the Finnish fuscus subspecies migrated on a south-southeastern course towards Ukraine and the Bosporus, Turkey. Only one of the transferred gulls could be tracked long enough to accurately determine the migratory behaviour: this bird from the intermedius subspecies left Finland on a south-southeasterly course towards the Ukraine, where transmission ceased. Thus, this gull resembled the migratory behaviour of the fuscus subspecies. One bird from the cross-breeding experiments wintered in Libya, but the migratory behaviour remained unknown due to the lack of positional data.

<p>(Sisargas (Galicia, Spain); Delta (Ebro delta, Spain); Moerdjik (The Netherlands); Häme ... more <p>(Sisargas (Galicia, Spain); Delta (Ebro delta, Spain); Moerdjik (The Netherlands); Häme (Finland); Kokkola (Finland). Häme and Kokkola are long-distance migrants. Different symbols denote subspecies: circles <i>L f</i>.<i>fuscus</i>, triangles <i>Lf</i>. <i>Intermedius</i>, squares <i>Lf</i>.<i>graellsii</i></p

<p>Mean, SE and SD.</p

<p>(Sisargas (Galicia, Spain); Delta (Ebro delta, Spain); Moerdjik (The Netherlands); Häme ... more <p>(Sisargas (Galicia, Spain); Delta (Ebro delta, Spain); Moerdjik (The Netherlands); Häme (Finland); Kokkola (Finland). Significant differences among populations are denoted by letters.</p><p>^ab denote differences among populations.</p><p>Pathogen prevalence (current protozoan infections and viral serology, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118279#sec002&quot; target="_blank">methods</a>) in the five populations of the study.</p

<p>Mean, SE and SD.</p

<p>Short-distance migrants: (Sisargas (Galicia, Spain); Delta (Ebro delta, Spain); Moerdjik... more <p>Short-distance migrants: (Sisargas (Galicia, Spain); Delta (Ebro delta, Spain); Moerdjik (The Netherlands); Long-distance migrants: Häme (Finland); Kokkola (Finland). Units: natural antibodies (-log₂ agglutination score), complement (-log₂ lysis score), IgY, Haptoglobin and Lysozyme (Optical density). Higher OD values indicate lower lysozyme.</p><p>^abc denote differences among populations in post-hoc statistical analyses.</p><p>Mean ±SD for immunological parameters in the five locations of the study.</p

During migratory journeys, birds may become displaced from their normal migratory route. Experime... more During migratory journeys, birds may become displaced from their normal migratory route. Experimental evidence has shown that adult birds can correct for such displacements and return to their goal. However, the nature of the cues used by migratory birds to perform long distance navigation is still debated. In this experiment we subjected adult lesser black-backed gulls migrating from their Finnish/Russian breeding grounds (from > 60°N) to Africa (to < 5°N) to sensory manipulation, to determine the sensory systems required for navigation. We translocated birds westward (1080 km) or eastward (885 km) to simulate natural navigational challenges. When translocated westwards and outside their migratory corridor birds with olfactory nerve section kept a clear directional preference (southerly) but were unable to compensate for the displacement, while intact birds and gulls with the ophthalmic branch of the trigeminal nerve sectioned oriented towards their population-specific migrat...

Being faced with unknown environments is a concomitant challenge of species' range expansions... more Being faced with unknown environments is a concomitant challenge of species' range expansions. Strategies to cope with this challenge include the adaptation to local conditions and a flexibility in resource exploitation. The gulls of the <i>Larus argentatus-fuscus-cachinnans</i> group form a system in which ecological flexibility might have enabled them to expand their range considerably, and to colonize urban environments. However, on a population level both flexibility and local adaptation lead to signatures of differential habitat use in different environments, and these processes are not easily distinguished. Using the lesser black-backed gull (<i>Larus fuscus</i>) as a system, we put both flexibility and local adaptation to a test. We compare habitat use between two spatially separated populations, and use a translocation experiment during which individuals were released into novel environment. The experiment revealed that on a population-level flexi...

The ability to control infections is a key trait for migrants that must be balanced against other... more The ability to control infections is a key trait for migrants that must be balanced against other costly features of the migratory life. In this study we explored the links between migration and disease ecology by examining natural variation in parasite exposure and immunity in several populations of Lesser Black-backed Gulls (Larus fuscus) with different migratory strategies. We found higher activity of natural antibodies in long distance migrants from the nominate subspecies L.f.fuscus. Circulating levels of IgY showed large variation at the pop-ulation level, while immune parameters associated with antimicrobial activity showed exten-sive variation at the individual level irrespective of population or migratory strategy. Pathogen prevalence showed large geographical variation. However, the seroprevalence of one of the gull-specific subtypes of avian influenza (H16) was associated to the migratory strategy, with lower prevalence among the long-distance migrants, suggesting that mi...

During migratory journeys, birds may become displaced from their normal migratory route. Experime... more During migratory journeys, birds may become displaced from their normal migratory route. Experimental evidence has shown that adult birds can correct for such displacements and return to their goal. However, the nature of the cues used by migratory birds to perform long distance navigation is still debated. In this experiment we subjected adult lesser black-backed gulls migrating from their Finnish/Russian breeding grounds (from > 60°N) to Africa (to < 5°N) to sensory manipulation, to determine the sensory systems required for navigation. We translocated birds westward (1080 km) or eastward (885 km) to simulate natural navigational challenges. When translocated westwards and outside their migratory corridor birds with olfactory nerve section kept a clear directional preference (southerly) but were unable to compensate for the displacement, while intact birds and gulls with the ophthalmic branch of the trigeminal nerve sectioned oriented towards their population-specific migratory corridor. Thus, air-borne olfactory information seems to be important for migrating gulls to navigate successfully in some circumstances.

Being faced with unknown environments is a concomitant challenge of species' range expansions... more Being faced with unknown environments is a concomitant challenge of species' range expansions. Strategies to cope with this challenge include the adaptation to local conditions and a flexibility in resource exploitation. The gulls of the <i>Larus argentatus-fuscus-cachinnans</i> group form a system in which ecological flexibility might have enabled them to expand their range considerably, and to colonize urban environments. However, on a population level both flexibility and local adaptation lead to signatures of differential habitat use in different environments, and these processes are not easily distinguished. Using the lesser black-backed gull (<i>Larus fuscus</i>) as a system, we put both flexibility and local adaptation to a test. We compare habitat use between two spatially separated populations, and use a translocation experiment during which individuals were released into novel environment. The experiment revealed that on a population-level flexibility best explains the differences in habitat use between the two populations. We think that our results suggest that the range expansion and huge success of this species complex could be a result of its broad ecological niche and flexibility in the exploitation of resources. However, this also advises caution when using species distribution models to extrapolate habitat use across space.

Royal Society Open Science, 2017

Being faced with unknown environments is a concomitant challenge of species' range expansions. St... more Being faced with unknown environments is a concomitant challenge of species' range expansions. Strategies to cope with this challenge include the adaptation to local conditions and a flexibility in resource exploitation. The gulls of the Larus argentatus-fuscus-cachinnans group form a system in which ecological flexibility might have enabled them to expand their range considerably, and to colonize urban environments. However, on a population level both flexibility and local adaptation lead to signatures of differential habitat use in different environments, and these processes are not easily distinguished. Using the lesser black-backed gull (Larus fuscus) as a system, we put both flexibility and local adaptation to a

Global Ecology and Conservation, Apr 1, 2017

In contrast to many other gull species, nominate lesser black-backed gulls (Larus fuscus fuscus, ... more In contrast to many other gull species, nominate lesser black-backed gulls (Larus fuscus fuscus, nLBBG) have shown generally decreasing population trends throughout their breeding area in northern and eastern Fennoscandia over the past decades and are now red-listed. Interspecific competition, predation, increased disturbance, organochlorine poisoning and food shortages were suggested as main reasons for the overall decrease. Here we contribute to a better understanding of population declines by comparing foraging movements of satellite tracked adult gulls in three geographical areas of Finland (West, South, and East) that differ in their population trends. Our analysis examines potential differences and preferences in the feeding site behaviour of adult gulls. Our comparison of the three geographical areas showed that nLBBGs preferred feeding at fur farms in West Finland, waste dumps in South Finland, and lakes and fields in East Finland. We found individual gulls of this purportedly generalist species to be highly specialised in their foraging behaviour, particularly those that might be associated with their survival probabilities. We ms 23-Mar-2017

Scientific Reports, Nov 24, 2015

During migratory journeys, birds may become displaced from their normal migratory route. Experime... more During migratory journeys, birds may become displaced from their normal migratory route. Experimental evidence has shown that adult birds can correct for such displacements and return to their goal. However, the nature of the cues used by migratory birds to perform long distance navigation is still debated. In this experiment we subjected adult lesser black-backed gulls migrating from their Finnish/Russian breeding grounds (from >60°N) to Africa (to < 5°N) to sensory manipulation, to determine the sensory systems required for navigation. We translocated birds westward (1080 km) or eastward (885 km) to simulate natural navigational challenges. When translocated westwards and outside their migratory corridor birds with olfactory nerve section kept a clear directional preference (southerly) but were unable to compensate for the displacement, while intact birds and gulls with the ophthalmic branch of the trigeminal nerve sectioned oriented towards their population-specific migratory corridor. Thus, airborne olfactory information seems to be important for migrating gulls to navigate successfully in some circumstances.

Satellite tracking of the migratory pathways of first-year Lesser Black-backed Gulls Larus fuscus... more Satellite tracking of the migratory pathways of first-year Lesser Black-backed Gulls Larus fuscus departing from the breeding grounds of different subspecies. Vogelwelt 128: 141-148. The migratory behaviour of two Lesser Black-backed Gull Larus fuscus subspecies, fuscus and intermedius, was studied using satellite telemetry. To this end, first-year birds were equipped with satellite transmitters and released either at their natal site, or after transferring to a breeding site of the other subspecies. In addition, first-year birds from cross-breeding experiments between the two subspecies (fuscus x intermedius) were also equipped with satellite transmitters. In total, eleven first-year birds were successfully tracked during their initial autumn migration, at least one from each study group. First-year birds from the Danish intermedius subspecies migrated either southwest along the coast of the North Sea or through central Europe to Algeria. By contrast, first-year birds from the Finnish fuscus subspecies migrated on a south-southeastern course towards Ukraine and the Bosporus, Turkey. Only one of the transferred gulls could be tracked long enough to accurately determine the migratory behaviour: this bird from the intermedius subspecies left Finland on a south-southeasterly course towards the Ukraine, where transmission ceased. Thus, this gull resembled the migratory behaviour of the fuscus subspecies. One bird from the cross-breeding experiments wintered in Libya, but the migratory behaviour remained unknown due to the lack of positional data.

PLOS ONE, Feb 13, 2015

The ability to control infections is a key trait for migrants that must be balanced against other... more The ability to control infections is a key trait for migrants that must be balanced against other costly features of the migratory life. In this study we explored the links between migration and disease ecology by examining natural variation in parasite exposure and immunity in several populations of Lesser Black-backed Gulls (Larus fuscus) with different migratory strategies. We found higher activity of natural antibodies in long distance migrants from the nominate subspecies L.f.fuscus. Circulating levels of IgY showed large variation at the population level, while immune parameters associated with antimicrobial activity showed extensive variation at the individual level irrespective of population or migratory strategy. Pathogen prevalence showed large geographical variation. However, the seroprevalence of one of the gull-specific subtypes of avian influenza (H16) was associated to the migratory strategy, with lower prevalence among the long-distance migrants, suggesting that migration may play a role in disease dynamics of certain pathogens at the population level.

Ringing and Migration, 2008

Satellite tracking of the migratory pathways of first-year Lesser Black-backed Gulls Larus fuscus... more Satellite tracking of the migratory pathways of first-year Lesser Black-backed Gulls Larus fuscus departing from the breeding grounds of different subspecies. Vogelwelt 128: 141-148. The migratory behaviour of two Lesser Black-backed Gull Larus fuscus subspecies, fuscus and intermedius, was studied using satellite telemetry. To this end, first-year birds were equipped with satellite transmitters and released either at their natal site, or after transferring to a breeding site of the other subspecies. In addition, first-year birds from cross-breeding experiments between the two subspecies (fuscus x intermedius) were also equipped with satellite transmitters. In total, eleven first-year birds were successfully tracked during their initial autumn migration, at least one from each study group. First-year birds from the Danish intermedius subspecies migrated either southwest along the coast of the North Sea or through central Europe to Algeria. By contrast, first-year birds from the Finnish fuscus subspecies migrated on a south-southeastern course towards Ukraine and the Bosporus, Turkey. Only one of the transferred gulls could be tracked long enough to accurately determine the migratory behaviour: this bird from the intermedius subspecies left Finland on a south-southeasterly course towards the Ukraine, where transmission ceased. Thus, this gull resembled the migratory behaviour of the fuscus subspecies. One bird from the cross-breeding experiments wintered in Libya, but the migratory behaviour remained unknown due to the lack of positional data.

<p>(Sisargas (Galicia, Spain); Delta (Ebro delta, Spain); Moerdjik (The Netherlands); Häme ... more <p>(Sisargas (Galicia, Spain); Delta (Ebro delta, Spain); Moerdjik (The Netherlands); Häme (Finland); Kokkola (Finland). Häme and Kokkola are long-distance migrants. Different symbols denote subspecies: circles <i>L f</i>.<i>fuscus</i>, triangles <i>Lf</i>. <i>Intermedius</i>, squares <i>Lf</i>.<i>graellsii</i></p

<p>Mean, SE and SD.</p

<p>(Sisargas (Galicia, Spain); Delta (Ebro delta, Spain); Moerdjik (The Netherlands); Häme ... more <p>(Sisargas (Galicia, Spain); Delta (Ebro delta, Spain); Moerdjik (The Netherlands); Häme (Finland); Kokkola (Finland). Significant differences among populations are denoted by letters.</p><p>^ab denote differences among populations.</p><p>Pathogen prevalence (current protozoan infections and viral serology, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118279#sec002&quot; target="_blank">methods</a>) in the five populations of the study.</p

<p>Mean, SE and SD.</p

<p>Short-distance migrants: (Sisargas (Galicia, Spain); Delta (Ebro delta, Spain); Moerdjik... more <p>Short-distance migrants: (Sisargas (Galicia, Spain); Delta (Ebro delta, Spain); Moerdjik (The Netherlands); Long-distance migrants: Häme (Finland); Kokkola (Finland). Units: natural antibodies (-log₂ agglutination score), complement (-log₂ lysis score), IgY, Haptoglobin and Lysozyme (Optical density). Higher OD values indicate lower lysozyme.</p><p>^abc denote differences among populations in post-hoc statistical analyses.</p><p>Mean ±SD for immunological parameters in the five locations of the study.</p

During migratory journeys, birds may become displaced from their normal migratory route. Experime... more During migratory journeys, birds may become displaced from their normal migratory route. Experimental evidence has shown that adult birds can correct for such displacements and return to their goal. However, the nature of the cues used by migratory birds to perform long distance navigation is still debated. In this experiment we subjected adult lesser black-backed gulls migrating from their Finnish/Russian breeding grounds (from > 60°N) to Africa (to < 5°N) to sensory manipulation, to determine the sensory systems required for navigation. We translocated birds westward (1080 km) or eastward (885 km) to simulate natural navigational challenges. When translocated westwards and outside their migratory corridor birds with olfactory nerve section kept a clear directional preference (southerly) but were unable to compensate for the displacement, while intact birds and gulls with the ophthalmic branch of the trigeminal nerve sectioned oriented towards their population-specific migrat...

Being faced with unknown environments is a concomitant challenge of species' range expansions... more Being faced with unknown environments is a concomitant challenge of species' range expansions. Strategies to cope with this challenge include the adaptation to local conditions and a flexibility in resource exploitation. The gulls of the <i>Larus argentatus-fuscus-cachinnans</i> group form a system in which ecological flexibility might have enabled them to expand their range considerably, and to colonize urban environments. However, on a population level both flexibility and local adaptation lead to signatures of differential habitat use in different environments, and these processes are not easily distinguished. Using the lesser black-backed gull (<i>Larus fuscus</i>) as a system, we put both flexibility and local adaptation to a test. We compare habitat use between two spatially separated populations, and use a translocation experiment during which individuals were released into novel environment. The experiment revealed that on a population-level flexi...

The ability to control infections is a key trait for migrants that must be balanced against other... more The ability to control infections is a key trait for migrants that must be balanced against other costly features of the migratory life. In this study we explored the links between migration and disease ecology by examining natural variation in parasite exposure and immunity in several populations of Lesser Black-backed Gulls (Larus fuscus) with different migratory strategies. We found higher activity of natural antibodies in long distance migrants from the nominate subspecies L.f.fuscus. Circulating levels of IgY showed large variation at the pop-ulation level, while immune parameters associated with antimicrobial activity showed exten-sive variation at the individual level irrespective of population or migratory strategy. Pathogen prevalence showed large geographical variation. However, the seroprevalence of one of the gull-specific subtypes of avian influenza (H16) was associated to the migratory strategy, with lower prevalence among the long-distance migrants, suggesting that mi...