Geology topics

P. Clausen

Publications and source records attributed to P. Clausen.

3 recordsLinked to original sources

USGS2024

Predicting the response of a long-distance migrant to changing environmental conditions in winter

Access to high-quality food is critical for long-distance migrants to provide energy for migration and arrival at breeding grounds in good condition. We studied effects of changing abundance and availability of a marine food, common eelgrass ( Zostera marina L.), on an arctic-breeding, migratory goose, black brant ( Brant bernicla nigricans Lawrence 1846), at a key non-breeding site, Bahía San Quintín, Mexico. Eelgrass, the primary food of brant, is consumed when exposed by the tide or within reach from the water's surface. Using an individual-based model, we predicted effects of observed changes (1991–2013) in parameters influencing food abundance and availability: eelgrass biomass (abundance), eelgrass shoot length (availability, as longer shoots more within reach), brant population size (availability, as competition greater with more birds), and sea level (availability, as less food within reach when sea level higher). The model predicted that the ability to gain enough energy to migrate was most strongly influenced by eelgrass biomass (threshold January biomass for migration = 60 g m −2 dry mass). Conversely, annual variation in population size (except for 1998), was relatively low, and variation in eelgrass shoot length and sea level were not strongly related to ability to migrate. We used observed data on brant body mass at Bahía San Quintín and annual survival to test for effects of eelgrass biomass in the real system. The lowest observed values of body mass and survival were in years when biomass was below 60 g m −2 , although in some years of low biomass body mass and/or survival was higher. This suggests that the real birds may have some capacity to compensate to meet their energy demands when eelgrass biomass is low. We discuss consequences for brant population trends and conservation.

Baja California↗

USGS2019

Current trends and future directions in swan research: Insights from the 6th International Swan Symposium

Given their popularity with researchers and public alike, together with their welldocumented importance in aquatic and terrestrial ecosystems, fundamental and applied research on swans continues to develop in the 21st century. The 6th International Swan Symposium (6th ISS), was held at the Estonian University of Life Sciences in Tartu, Estonia, in October 2018. The symposium brought together 101 delegates from 17 countries, with presentations on a range of topics on Cygnus and Coscoroba species, including monitoring, habitat and resource use, demography, movements and migration, and threats and conservation. The proceedings of the 6th ISS in this special issue of Wildfowl include select papers on swan research presented at the 6th ISS, covering a wide range of species, systems and issues. This paper presents a synthesis of the 6th ISS and an overview of current trends and future directions in swan research. Despite progress on many topics, southern hemisphere swan species continue to receive less attention than their northern hemisphere counterparts, whilst facing many of the same pressures. It is clear that, given the challenges facing swan researchers in the twenty-first century, international cooperation will continue to be vital. Swans are highly mobile animals and many populations undertake migrations spanning thousands of kilometres, and crucially do not recognise human geographic and political borders. Such international collaborations will be particularly important in coordinating future monitoring and conservation activities. The IUCN-SSC/Wetlands International Swan Specialist Group (SSG) will continue to facilitate international collaborations and communication among the global network of swan researchers, through its activities, website and annual newsletter. Given the substantial challenges and knowledge gaps documented here, there is no doubt that swan researchers will continue to benefit from regular symposia to share information and develop collaborations towards understanding and addressing emerging conservation issues. As such, we recommend holding International Swan Symposia every 4–5 years.

Wildfowl↗

USGS2019

Conservation status of the world’s swan populations, Cygnus sp. and Coscoroba sp.: a review of current trends and gaps in knowledge

Recent estimates of the world’s swan Cygnus sp. populations indicate that there are currently between 1.5–1.6 million birds in 8 species, including the Coscoroba Swan Coscoroba coscoroba as an honorary swan. Monitoring programmes in Europe and North America indicate that most populations increased following the introduction of national and international legislation to protect the species during the early- to mid-20th century. A switch from feeding primarily on aquatic vegetation to foraging on farmland (especially high-energy arable crops) in winter during the second half of the 20th century, is also considered a contributing factor. Trumpeter Swans Cygnus buccinator famously increased from just 69 individuals known to exist in 1935 (although small numbers were missed) to c. 76,000 at the present time, and most of the northern hemisphere swan populations have continued to show increasing/stable trends over the last 20 years. The exception to this pattern is a decline since 1995 in the Northwest European Bewick’s Swan population, following an increase in its population size during the 1970s–1980s, which is now being addressed through implementation of an International Single Species Action Plan. A proposal to change enforcement regulations of the Migratory Bird Treaty Act in the United States is also of concern, as potentially undermining protection for Trumpeter Swans in North America, illustrating the importance of politics and legislation as well as on-the-ground measures for species conservation. Elsewhere, less is known about the trends and conservation status for swans in central and eastern Asia, though count and research programmes introduced in China, added to those underway in Japan and Korea, have recently greatly enhanced our knowledge of swan populations on the East Asian flyway. Trends for the Black Swan Cygnus atratus in Australia and for the Black-necked Swan Cygnus melancoryphus in South America are also poorly known, because of the large numbers involved for the former and a lack of coordinated counts across difficult terrain for the latter. These southern hemisphere species are considered vulnerable to water resource developments ( i.e . where diversion of water is shrinking wetlands), and to droughts associated with El Nino events and climate change. More extensive monitoring is therefore required to determine whether swan populations and species are stable, fluctuating or in decline.

Wildfowl↗