Patterns of Post-Breeding Dispersal of Sandwich Terns (Thalasseus sandvicensis) in Danish Waters
(2021) BION02 20211Degree Projects in Biology
- Abstract
- Like many other terns, European Sandwich Terns (Thalasseus sandvicensis) exhibit a period of post-breeding dispersal before migrating to their wintering grounds in Africa. In order to understand the significance of Danish waters for these movements, I analysed the post-breeding phenology of Sandwich Terns at nine roosting sites and determined their overall distribution throughout Denmark by using count data from the online database DOFbasen. I assessed habitat characteristics of important roosting sites and evaluated (human) disturbances with data recorded in the field. Furthermore, I explored changes in body condition over the season for adults and juveniles that were caught during night catches from July to August in West Denmark. I used... (More)
- Like many other terns, European Sandwich Terns (Thalasseus sandvicensis) exhibit a period of post-breeding dispersal before migrating to their wintering grounds in Africa. In order to understand the significance of Danish waters for these movements, I analysed the post-breeding phenology of Sandwich Terns at nine roosting sites and determined their overall distribution throughout Denmark by using count data from the online database DOFbasen. I assessed habitat characteristics of important roosting sites and evaluated (human) disturbances with data recorded in the field. Furthermore, I explored changes in body condition over the season for adults and juveniles that were caught during night catches from July to August in West Denmark. I used resightings of individually marked Sandwich Terns to assess of use of Danish waters by terns of different geographical origin and calculated stopover durations and abundance estimates on Fanø, Southwest Denmark. The results of this study show, that maximum numbers of roosting Sandwich Terns occurred earlier along the West Jutland Coast (from Southwest to North Denmark) than on the East Jutland Coast (East and Southeast Denmark). Together with the results of site characteristics that reflect the habitat preferences of their key prey species, it seems that phenological patterns of Sandwich Terns as piscivores are highly influenced by the phenology and relative abundance of their prey. Results from the resighting data suggest that the proximity of breeding colonies to Danish post-breeding roosting sites might influence the phenology patterns as well. Based on the results from Fanø, it was estimated that most individuals stayed for only a few days and that approx. 10,000 Sandwich Terns visited the island during the post-breeding period. Only juvenile Sandwich Terns significantly increased their body condition, perhaps reflecting the importance of parents to invest in energy stores of their offspring. An observed average disturbance rate of more than one disturbance per hour underlines the need for protected roosting spots on beaches with high human activity. These findings in combination with resightings of Sandwich Terns dispersing from various European countries highlight the international importance of Danish waters during the period of post-breeding dispersal. (Less)
- Popular Abstract
- Denmark: An International Hotspot for Sandwich Terns
Just like us humans, Sandwich Terns prefer sandy beaches with shallow waters in the summer. And where would it be better to find many of such beaches if not in Denmark?
Thousands of Sandwich Terns from various European countries fly to Denmark after the end of their breeding season and before they migrate to Africa. These movements are called post-breeding dispersal and play an important role in the life cycle of a Sandwich Tern.
For this project, I analysed the occurrence of Sandwich Terns in Demark from June until October in order to understand the importance of this region during the period of post-breeding dispersal. I used count data of roosting terns, measurements that... (More) - Denmark: An International Hotspot for Sandwich Terns
Just like us humans, Sandwich Terns prefer sandy beaches with shallow waters in the summer. And where would it be better to find many of such beaches if not in Denmark?
Thousands of Sandwich Terns from various European countries fly to Denmark after the end of their breeding season and before they migrate to Africa. These movements are called post-breeding dispersal and play an important role in the life cycle of a Sandwich Tern.
For this project, I analysed the occurrence of Sandwich Terns in Demark from June until October in order to understand the importance of this region during the period of post-breeding dispersal. I used count data of roosting terns, measurements that were taken during night catches and resightings of individually marked birds.
Most of the Sandwich Terns that fly to Denmark are families because the juveniles are still highly depended on their parents after leaving the breeding colony. The feeding method of Sandwich Terns as piscivorous is a very complex technique and requires a lot of practice before mastering it. It can take months for the juveniles to learn it and they would not survive without support and learning from their parents. Therefore, adult Sandwich Terns continue feeding their ever-hungry offspring throughout the summer. This parental support is reflected by the development of body mass of the juveniles from July to August, while the body mass of adults did not change.
The seasonal occurrence (phenology) of Sandwich Terns showed differences between the Danish West Coast and the east side of Denmark. More precisely, maximum numbers of Sandwich Terns are seen along the Danish West Coast in the beginning of August while maximum numbers along the East Coast are seen towards the end of August. This is very likely influenced by the phenology and distribution of the fish that the terns eat. One of their favourite fish species, the Sandeel, is particular abundant in the Danish North Sea. However, Sandeels have an overwintering phase during which they are buried in the sand, starting in August/September. Before Sandeels disappear into the sand in the Danish North Sea, the Danish West Coast seems to be more attractive to Sandwich Terns than the East Coast. After that, Sandwich Terns re-distribute themselves more and might feed on their other preferred fish species: Sprat and Herring, which are abundant in both the North Sea and Kattegat. The occurrence of terns may also depend on from where the Sandwich Terns started their journey to Denmark. For example, German birds are mainly seen in Southwest Denmark, while birds from Southeast Denmark are more often seen in East Denmark.
Not only the distribution of fish is important for Sandwich Terns, they also need safe and peaceful roosting sites. However, Sandwich Terns prefer the same beaches as most people do, and where there are many people, there are also many disturbances for the terns. The more frequently the terns get disturbed the less terns remain on the beach. Such disturbances lead to difficulties for the adults to find their offspring again. Furthermore, the terns might be forced to move to less suitable roosting sites that are further away from the best foraging areas.
Analysis of resightings of individually marked Sandwich Terns indicated that in a single season more than 10,000 birds can visit the island of Fanø in Southwest Denmark, making Fanø an internationally important roosting site for Sandwich Terns. Many birds from Germany or the Netherlands come to profit from its rich feeding areas, but also birds from Poland or Great Britain have been seen on Fanø. Taking all of this into account, one message from the study is that it would be relevant to consider protecting important post-breeding roosting sites so that the Sandwich Terns can prepare for their migratory journey to Africa without being disturbed. So, the next time you go to a beach and see a lot of birds, watch out for the Sandwich Terns!
Master’s Degree Project in Biology, Specialisation in Animal Ecology. 45 credits 2021
Department of Biology, Lund University
Advisor: Thomas Bregnballe & Thomas Alerstam
Department of Ecoscience, Aarhus University
Department of Biology, Evolutionary Ecology, Lund University (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9069177
- author
- Vergin, Lisa
- supervisor
- organization
- course
- BION02 20211
- year
- 2021
- type
- H2 - Master's Degree (Two Years)
- subject
- language
- English
- id
- 9069177
- date added to LUP
- 2021-12-16 12:49:43
- date last changed
- 2021-12-16 12:49:43
@misc{9069177,
abstract = {{Like many other terns, European Sandwich Terns (Thalasseus sandvicensis) exhibit a period of post-breeding dispersal before migrating to their wintering grounds in Africa. In order to understand the significance of Danish waters for these movements, I analysed the post-breeding phenology of Sandwich Terns at nine roosting sites and determined their overall distribution throughout Denmark by using count data from the online database DOFbasen. I assessed habitat characteristics of important roosting sites and evaluated (human) disturbances with data recorded in the field. Furthermore, I explored changes in body condition over the season for adults and juveniles that were caught during night catches from July to August in West Denmark. I used resightings of individually marked Sandwich Terns to assess of use of Danish waters by terns of different geographical origin and calculated stopover durations and abundance estimates on Fanø, Southwest Denmark. The results of this study show, that maximum numbers of roosting Sandwich Terns occurred earlier along the West Jutland Coast (from Southwest to North Denmark) than on the East Jutland Coast (East and Southeast Denmark). Together with the results of site characteristics that reflect the habitat preferences of their key prey species, it seems that phenological patterns of Sandwich Terns as piscivores are highly influenced by the phenology and relative abundance of their prey. Results from the resighting data suggest that the proximity of breeding colonies to Danish post-breeding roosting sites might influence the phenology patterns as well. Based on the results from Fanø, it was estimated that most individuals stayed for only a few days and that approx. 10,000 Sandwich Terns visited the island during the post-breeding period. Only juvenile Sandwich Terns significantly increased their body condition, perhaps reflecting the importance of parents to invest in energy stores of their offspring. An observed average disturbance rate of more than one disturbance per hour underlines the need for protected roosting spots on beaches with high human activity. These findings in combination with resightings of Sandwich Terns dispersing from various European countries highlight the international importance of Danish waters during the period of post-breeding dispersal.}},
author = {{Vergin, Lisa}},
language = {{eng}},
note = {{Student Paper}},
title = {{Patterns of Post-Breeding Dispersal of Sandwich Terns (Thalasseus sandvicensis) in Danish Waters}},
year = {{2021}},
}