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Autumn fueling behavior in passerines in relation to migratory distance and daylength

Engert, Elana Rae (2021) BION02 20202
Degree Projects in Biology
Abstract
Many songbird species that breed at northern latitudes migrate long distances each autumn, while others brave the cold winter. Long-distance migrants have physiological adaptations that allow them to rapidly gain weight at stopover sites during migration for optimal speed. There is some evidence from closely related species that birds with a longer migration distance deposit fuel faster. However, few studies have compared the maximum fueling rates and limitations of different species with long, medium, and short migration distances. In this study, I compare the fueling behaviors and the potential physiological costs of fueling at a stopover on autumn migration for 5 songbird species migrating through Sweden at the Baltic Sea; Willow... (More)
Many songbird species that breed at northern latitudes migrate long distances each autumn, while others brave the cold winter. Long-distance migrants have physiological adaptations that allow them to rapidly gain weight at stopover sites during migration for optimal speed. There is some evidence from closely related species that birds with a longer migration distance deposit fuel faster. However, few studies have compared the maximum fueling rates and limitations of different species with long, medium, and short migration distances. In this study, I compare the fueling behaviors and the potential physiological costs of fueling at a stopover on autumn migration for 5 songbird species migrating through Sweden at the Baltic Sea; Willow Warbler Phylloscopus trochilus, Lesser Whitethroat Sylvia curruca, Common Chiffchaff Phylloscopus collybita, European Robin Erithacus rubecula, and Blue Tit Cyanistes caeruleus. Each species sustained a high fuel deposition rate for only a few days and all levelled off at a specific fuel load, the long-distance migrants, Willow Warblers and Lesser Whitethroats, depositing the largest fuel loads. All species ceased to increase in mass when they reached a certain fuel load despite unlimited access to food and ample time for foraging, suggesting some physiological control of the maximum fuel load reached at a stopover. Blue Tits, Willow Warblers and Lesser Whitethroats had the highest fuel deposition rates. Blue tits are irruptive migrants that winter at northern latitudes in Scandinavia, while Willow Warblers and Lesser Whitethroats are long-distance migrants that winter in the tropics. European Robins and Common Chiffchaffs that winter in the temperate Mediterranean had the lowest fuel deposition rates. (Less)
Popular Abstract
Songbirds win the avian extreme eating contest
Many wild animals have evolved to cope with extreme environments for living. For instance, sea otters live in the cold waters of the Pacific Ocean, have a high metabolism, and eat up to 30% of their body weight each day in order to stay warm. Waders, long-legged birds that probe mudflats for food, can migrate long distances and gain weight at an impressively fast pace. They can store 15% of their body weight in fat per day as fuel for their long flights. Songbirds, however, are the heavy-weight champions.

Many bird species live in cold environments in the winter or perform extreme migrations to escape harsh winter conditions. Some birds migrate very long distances, for example, between... (More)
Songbirds win the avian extreme eating contest
Many wild animals have evolved to cope with extreme environments for living. For instance, sea otters live in the cold waters of the Pacific Ocean, have a high metabolism, and eat up to 30% of their body weight each day in order to stay warm. Waders, long-legged birds that probe mudflats for food, can migrate long distances and gain weight at an impressively fast pace. They can store 15% of their body weight in fat per day as fuel for their long flights. Songbirds, however, are the heavy-weight champions.

Many bird species live in cold environments in the winter or perform extreme migrations to escape harsh winter conditions. Some birds migrate very long distances, for example, between Scandinavia and sub-Saharan Africa. Others go a shorter distance, to the Mediterranean, for their non-breeding period. Still others stay in Scandinavia all winter. These strategies use a lot of energy, which comes in the form of food or stored fat. Birds that migrate are known for their ability to get very fat in a short amount of time when they rest between flights. In the wild, their ability to gain weight is limited by the amount of food available, competition for food, the amount of time they can spend looking for food, or the risk of getting eaten themselves.

I wanted to know what would happen if songbirds were given unlimited food and time to feed. Would the long-distance migrants gain weight faster than the others with the goal of reaching their distant wintering area in time? Would they get even fatter if the lights were switched on all night, allowing more time each day for feeding? In order to answer these questions, I captured 74 songbirds of 5 species on migration at Ottenby Bird Observatory in south-east Sweden, put them in bird cages temporarily and provided them with an all-you-can-eat buffet of meal worms. Several days later, after they had eaten their fill, I released them so that they could resume their migratory journey.

How fast can a bird get fat?
It turns out that songbirds get fat with record speed when they can feed throughout the day and night. Long and short distance migrants gained 20% of their body weight in a day on average when they had non-stop daytime feeding conditions. One impressive bird, a Blue Tit, gained 35% of its own weight in a day. That’s like an average-sized person (weighing 60 kg) gaining 21 kilos in 24 hours. Medium distance migrants that spend the winter in the mild climate of Central Europe gained weight more slowly, at 12% per day with lights on at night. This could mean that birds that migrate the farthest and experience the coldest winters need to gain weight the fastest.

Long distance migrants that fed only during the daytime gained 13% of their body weight per day on average, which is the same as the maximum found in nature. Assuming that 13% is the best possible rate for long distance migrants, the rate at which birds gain weight in nature can be compared to this value. Using this information, habitat quality can be assessed for different places that songbirds use along the migration route. This approach could potentially be used to focus conservation efforts for declining songbird species.


Master’s Degree Project in Biology 45 credits 2021
Department of Biology, Lund University

Advisor: Susanne Åkesson
Department of Biology, Lund University (Less)
Please use this url to cite or link to this publication:
author
Engert, Elana Rae
supervisor
organization
course
BION02 20202
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
9061441
date added to LUP
2021-07-09 10:22:46
date last changed
2021-07-09 10:22:46
@misc{9061441,
  abstract     = {{Many songbird species that breed at northern latitudes migrate long distances each autumn, while others brave the cold winter. Long-distance migrants have physiological adaptations that allow them to rapidly gain weight at stopover sites during migration for optimal speed. There is some evidence from closely related species that birds with a longer migration distance deposit fuel faster. However, few studies have compared the maximum fueling rates and limitations of different species with long, medium, and short migration distances. In this study, I compare the fueling behaviors and the potential physiological costs of fueling at a stopover on autumn migration for 5 songbird species migrating through Sweden at the Baltic Sea; Willow Warbler Phylloscopus trochilus, Lesser Whitethroat Sylvia curruca, Common Chiffchaff Phylloscopus collybita, European Robin Erithacus rubecula, and Blue Tit Cyanistes caeruleus. Each species sustained a high fuel deposition rate for only a few days and all levelled off at a specific fuel load, the long-distance migrants, Willow Warblers and Lesser Whitethroats, depositing the largest fuel loads. All species ceased to increase in mass when they reached a certain fuel load despite unlimited access to food and ample time for foraging, suggesting some physiological control of the maximum fuel load reached at a stopover. Blue Tits, Willow Warblers and Lesser Whitethroats had the highest fuel deposition rates. Blue tits are irruptive migrants that winter at northern latitudes in Scandinavia, while Willow Warblers and Lesser Whitethroats are long-distance migrants that winter in the tropics. European Robins and Common Chiffchaffs that winter in the temperate Mediterranean had the lowest fuel deposition rates.}},
  author       = {{Engert, Elana Rae}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Autumn fueling behavior in passerines in relation to migratory distance and daylength}},
  year         = {{2021}},
}