Energetic consequences of a major change in habitat use: endangered Brent Geese Branta bernicla hrota losing their main food resource

Abstract

Coastal seagrasses are declining at increasing rates worldwide, forcing herbivores previously reliant on these habitats to abandon them in search of alternative ways to fulfil their daily energy budgets. After two decades of declining seagrass abundance in Mariager Fjord, Denmark, the Svalbard breeding population of Light‐bellied Brent Geese Branta bernicla hrota has experienced substantial changes in habitat use at this traditional autumn staging area. Declines in seagrasses have caused birds to depend increasingly on Sea Lettuce Ulva lactuca in recent years, and forced birds into terrestrial habitats such as saltmarsh and winter wheat. In contrast to those birds exploiting aquatic habitats, birds relying on these new habitats showed higher energy expenditure and failed to balance their energy budget. Eelgrass (Zostera) was energetically superior to other food resources, with marine Ulva being second best. Predicted body mass development under two different scenarios indicate that present habitat use resulted in a midwinter body mass around 122 g lower than just 20 years ago, equivalent to c. 9.4% of Brent Goose body weight. Even after controlling for inter‐annual differences in thermoregulatory costs, the effect of changes in habitat use translated into a body mass reduction of c. 56 g, which could adversely affect survival and future reproduction. Flyway‐wide declines in Zostera abundance and further reductions in traditional habitats due to climate change give cause to reassess projected population trends and consequent management implications for the East Atlantic flyway population of Light‐bellied Brent Geese.

Long-term Patterns of Eelgrass (Zostera marina) Occurrence and Associated Herbivorous Waterbirds in a Danish Coastal Inlet

“…We used body mass estimates from Simmons (1977, 1980) for wigeon (0.70 kg) and coot (0.76 kg) and an average autumn mass of 1.6 kg for lightbellied brent goose (from Clausen et al, 2012), and subsequently estimated the birds daily energy expenditure, DEE in kJ/day by three different allometric relationships. The first is from Drent et al (1978/79):…”

Philopatry in a changing world: response of pink-footed geese Anser brachyrhynchus to the loss of a key autumn staging area due to restoration of Filsø Lake, Denmark

“…The switch to an agricultural diet characteristic of both this population (Fox et al 2005) and other species of geese (Rosin et al 2012) opened the door to an almost inexhaustible food resource in the Danish landscape, and the availability of staging sites during the autumn migration may therefore depend more strongly on the relative proximity of secure roosting areas rather than specific food resources. As a consequence, philopatric waterfowl species exploiting cultivated areas might be much less susceptible to changes in staging areas than species targeting specific food sources much less available in a modern landscape (Clausen et al 2012;Fox et al 2011;Wang et al 2012). …”

“…As a consequence, species with restricted habitat choice and few available areas may suffer to a greater extent than species with flexible food choice and a selection of many and/or abundant habitats (Clausen et al 2012;Fox et al 2011). The ability of migrating birds to alter site use and migration patterns in response to habitat loss at stopover sites is dependent on the behavioral flexibility of individual species, and may theoretically affect departure load, mortality and phenology of individual birds (Weber et al 1999).…”

Effects of variation in food resources on foraging habitat use by wintering Hooded Cranes (Grus monacha)

“…Positive relationships between wader foraging habitat use and food abundance have also been found in other studies (Backwell et al 1998;Folmer et al 2010;Kuwae et al 2010), while Lantz et al (2011) and Beerens et al (2011) argue that food accessibility is also important. It is more profitable for cranes to raise the benefits/cost ratio of food accessibility simultaneously while avoiding deeper food items and harder sediment (Kuwae et al 2010;Baschuk et al 2012;Clausen et al 2012). Cranes also adopt effective strategies that protect their bills from wear and tear during the process of excavating, pecking and probing.…”