Foraging behaviour of brent geese, Branta b. bernicla, on grasslands: effects of sward length and nitrogen content

Abstract

Feeding behaviour and preferences of brent geese, Branta b. bernicla were observed on pastures of different sward lengths and nitrogen contents. On swards of 2.0-6.0 cm captive geese took larger bites and had a higher intake rate when feeding on 6-cm swards than when feeding on shorter ones. In the field wild geese chose 6-cm swards in preference to both shorter and longer ones. For unfertilized pastures there was a strong negative relationship between nitrogen content and sward height: 11-cm swards contained 2.8% nitrogen, 3.5-cm swards 4.2% nitrogen. Application of 75 kg N ha organically based fertilizer at the end of October eliminated this relationship between nitrogen content and sward height, swards of all heights then having a mean content of 4.1% N. On fertilized plots the geese preferred swards longer than 6 cm with no indication of a decrease in preference up to the maximum height investigated, 16 cm. Breaking strain of grass laminae was measured to give an indication of the proportion of strengthening tissues in the leaves and hence their digestibility. Apical laminae from longer swards had a higher breaking strain than those from shorter swards. Unfertilized swards had a higher breaking strain than fertilized swards but the difference in breaking strain between long and short swards was the same on fertilized and control treatments. These results are discussed in relation to the forage maturation hypothesis and are interpreted as indicating that the primary constraint on maximizing energy intake rates is not the reduced energy digestibility of older foliage but the reduced nitrogen content in the higher-biomass swards. We conclude that it is the balance between maximizing energy intake and nitrogen absorption rates which results in the observed preference for intermediate-height swards.

Variation in Elevation and Sward Height Facilitate Coexistence of Goose Species through Allometric Responses in Wetlands

“…Vegetation in lower elevation areas is often of higher quality (Olff et al 1997). Many experimental studies report that nitrogen content can affect herbivore habitat selection (Hassall et al 2001;Durant et al 2004). In our study, we failed to detect any relationship between nitrogen content and fecal densities, similar to a study on the Barnacle Goose (B. leucopsis) in The Netherlands (Si et al 2011), which was also based on field observations.…”

“…Plant quality generally decreases over the growing season with increasing plant height and biomass (van der Wal et al 2000). With increasing plant height, the nitrogen content decreases (Prins and Olff 1998;Hassall et al 2001), whereas the fiber content increases (Gekara et al 2005). Foragers face a trade-off between maximizing forage quantity and quality.…”

Distribution of Barnacle GeeseBranta leucopsisin Relation to Food Resources, Distance to Roosts, and the Location of Refuges

“…The eight tracked geese spent 80% of their foraging time in refuges, demonstrating the importance of the refuge system. experimental conditions, in particular to understand decisions that take place at a small scale (Riddington et al 1997, Hassall et al 2001, Bos et al 2004. However, processes that take place at the habitat scale have been investigated less often.…”

Feeding patch selection by herbivorous Anatidae: the influence of body size, and of plant quantity and quality

“…Indeed, geese have a high nitrogen requirement as a result of their relative inefficiency in incorporating protein because the proteins in plants and avian tissues have different amino acid profiles (Sedinger 1984). In the trade-off between quality and quantity, birds will therefore be expected to favour quality to a greater extent than mammalian herbivores Prins 1987, Stahl 2001).The 'forage maturation hypothesis' has been tested in brent geese Branta bernicla on pastures (Riddington et al 1997, Hassall et al 2001) and the birds did trade-off quantity for quality, and nitrogen apparently played a key role. They selected grass of intermediate height for which the intake rate of nitrogen is higher.…”