Metabolic Rates and Nighttime Energy Saving in Long-Distance versus ShortDistance Migratory Passerines

Abstract

Billions of birds migrate thousands of kilometres twice a year. The migration is an energetic challenge, with over 70% of the total energy expenditure being spent at stopover sites. There are different strategies birds can use to conserve energy, such as reducing the metabolic rate. This study aimed to investigate the potential nighttime energy saving in long-distance versus short-distance migrating passerines and what factors might influence the regulation of metabolic rate during stopover. This was investigated by studying the nighttime metabolic rate of 23 different passerine species. The study was done at Falsterbo Bird Observatory in Falsterbo, Sweden (55° 23’ 1.93” N, 12° 49’ 0.16” E) from the 4th of September 2023 until the 16th of October 2023. The results showed that long-distance migrants had a higher minimum metabolic rate and average resting metabolic rate during the night compared to short-distance migrants. However, there was no difference between the two migration groups when it came to the daytime resting metabolic rate. When it comes to energy saving there was no significant difference in nighttime energy saving (i.e., nighttime metabolic rate compared to daytime metabolic rate) between the two migration distances. Possible explanations could be that long-distance migrants turn into metabolic ‘super machines’, leading to higher metabolic rates at night. Due to less pressure during autumn migration compared to spring, there could be less need to conserve energy. Moreover, migratory restlessness could have masked any possible differences between the two groups. Body mass and ambient temperature were also shown to significantly affect metabolic rate, which is in line with previous research. More knowledge of the physiology of these migrating birds can help us better predict how they will respond to future environmental changes.

Popular Abstract

How Songbirds Manage Energy on Epic Journeys

Billions of birds travel thousands of kilometres twice a year during migration. This migration is like a big marathon, which costs a lot of energy. How do birds do it? How can a small animal like that have enough energy to fly to the other side of the earth?

Birds have clever ways to save energy. They can, for example, lower their metabolic rate. Metabolic rate is the pace at which your body burns calories to produce energy for all its functions. A lower metabolic rate will cost the body less energy to function. I wanted to find out if these migrating birds save energy at night by lowering their metabolic rate. I also wanted to see if there was a difference in this energy saving between birds that travel short distances and birds that travel long distances. Birds that travel short distances are birds that fly further down South in Europe or the North of Africa. Long-distance migrants fly past the Sahara.

I caught more than 100 birds from 23 different songbird species at Falsterbo Bird Observatory in the South of Sweden. This was done from September to October 2023. Each bird was measured and weighed. At night, they were put into glass chambers where air was pushed in and out through tubes. A machine measured how much oxygen each bird was using for the whole night. This could then be used to calculate each bird's metabolic rates at different times.

It turns out that the metabolic rate of long-distance migrating birds is higher compared to birds that migrate shorter distances. This can be because the further a bird needs to travel, the more fuel and muscle it needs to be able to make it. Long-distance migrants are possibly more efficient in processing food and building up large fuel reserves.

There is no difference in nighttime energy savings between the two migration groups. This might be because the data was collected during the autumn migration. In autumn, there is less urgency to migrate quickly compared to spring. During spring migration, birds benefit from finishing faster so they can select better territories. Another reason could be because of something called migratory restlessness. This is a restlessness that captive migrating birds can have at night because they want to migrate. So instead of resting at night, they are very active. This restlessness could have occurred in both migration groups. This means that this could have hidden any differences between the groups when it comes to saving energy at night.

Conservation
In the future, extreme weather events are likely to increase. This can be for example heatwaves. This will affect not only individuals but whole ecosystems. Songbirds, who have a higher metabolic rate than other birds, are more sensitive to things like increasing temperatures. Therefore, if we know more about how these migrating birds migrate and regulate their metabolic rate, we can better predict how they will respond to these changing climates. This will help us to protect them better.

Master’s Degree Project in Conservation Biology 45 credits 2024
Department of Biology, Lund University
Advisors: Andreas Nord & Fredrik Andreasson

• author: Vermorken, Louise
• supervisor: Fredrik Andreasson; Andreas Nord
• organization: Degree Projects in Biology
• course: BION02 20232
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9176023
• date added to LUP: 2024-10-03 14:24:53
• date last changed: 2024-10-03 14:24:53