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Testing the habitat choice of captive brent geese, branta bernicla, on manipulated vegetation characteristics in an experimental set-up

Timmer, M. (1998) Testing the habitat choice of captive brent geese, branta bernicla, on manipulated vegetation characteristics in an experimental set-up. Master's Thesis / Essay, Biology.

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Abstract

The habitat choice of geese depends on the food offer. This offer changes during the year. Brent Geese use only one third of the energetic content of their food, so they have to eat large quantities of relatively high-quality food. The geese maximise their net-energy intake by a shift from the improved grassland in early spring to the salt marsh vegetation in late spring. In this period they have to build up body reserves for the flight to their breeding grounds. So the geese need high quality of food. We want to know if geese are selecting for plant quality or biomass (quantity). In the field quality and quantity of food offer are usually associated. In this study we tried to test the effect of plant quality, quantity and salinity on the habitat choice of Brent Geese. The choice of the geese could be measured by observations of Brent Geese in an experimental cage of 4 x 4 m. Two types of experiments were done. The decision experiments with four Brent Geese and salt experiments with four Brent and two Barnacle Geese. During the decision experiments the geese could choose between two halves differing in quality (fertilised, unfertilised) or quantity (high biomass, low biomass). The behaviour and location of the geese were recorded. During the salt experiments the geese could choose between a vegetation sprayed with fresh and a vegetation sprayed with salt water. There is a difference in food choice between the experimental geese and the wild geese. The wild geese have to gain weight in spring so they feed on the vegetation with the highest quality at that moment. Wild geese spent more time in foraging an feed twice intensively. The experimental geese could forage 24 hours and spent more time in sleeping or grooming. The wild geese showed a clear preference for the fertilised vegetation. In most cases the highest biomass was on the fertilised parts of the vegetation. In the first experiment the geese choose for quantity (biomass) and there was no preference for the fertilised vegetation when there was no difference in biomass. In the second experiment, there was a preference for the fertilised vegetation, when there was no difference in biomass. The quantity of the food seemed to have no effect on the preference. However we showed that the geese can select on quantity and quality, it is not yet clear how the preference for vegetation can be independently explained by quantity or quality of the vegetation. Salt influences the food choice of the Brent Geese and the Barnacle Geese. Brent Geese choose for a vegetation with fresh water. Barnacle Geese also choose for a vegetation with fresh water. During the experiments with two Brent and two Barnacle Geese there was a difference in choice between the geese. The Brent Geese fed on the salt and the Barnacle Geese fed on the fresh vegetation. The food choice of the Brent Geese was influenced by the behaviour of the Barnacle Geese. Inter-specific competition (competition between two species) influences the food choice of the geese.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Biology
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 07:45
Last Modified: 15 Feb 2018 07:45
URI: http://fse.studenttheses.ub.rug.nl/id/eprint/9461

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