Agriculture and herbivorous waterfowl: a review of the scientific basis for improved management

Abstract

Swans, geese and some ducks (Anatidae) are obligate herbivores, many are important quarry species and all contribute to a variety of ecosystem services. Population growth and shifting ranges have led to increasing proximity to man and thus increasing conflicts. We review and synthesize the role of these birds as herbivores on agricultural land (cropland, rotational grassland and pasture) and other terrestrial habitats where conflict with human interests may occur. A bibliographic analysis of peer-reviewed papers (N = 359) shows that publication activity peaked in 1991-2000 in North America and 2000-2010 in Europe, and has decreased since. Taxonomic and geographical biases are obvious in research to date: Snow Goose Chen caerulescens was the most studied species (N = 98), and Canada Branta canadensis, Barnacle B. leucopsis and Brent geese B. bernicla all featured in more than 40 studies; most studies originated in northwest Europe or North America, very few have been carried out in Asia and European Russia. On the basis of nutrient/energy budgets of herbivorous waterfowl, it is evident that dense single-species crops (such as rotational grassland, early-growth cereals and root crops) and spilled grain in agricultural landscapes offer elevated energetic and nutritional intake rates of food of higher quality compared to natural or semi-natural vegetation. Hence, although affected by seasonal nutritional demands, proximity to roost, field size, disturbance levels, access to water, food depletion and snow cover, agricultural landscapes tend to offer superior foraging opportunities over natural habitats, creating potential conflict with agriculture. Herbivorous waterfowl select for high protein, soluble carbohydrate and water content, high digestibility as well as low fibre and phenolic compounds, but intake rates from grazing varied with goose body and bill morphology, creating species-specific loci for conflict. Crop damage by trampling and puddling has not been demonstrated convincingly, nor do waterfowl faeces deter grazing stock, but where consumption of crops evidently reduces yields this causes conflict with farmers. Studies show that it is difficult and expensive to assess the precise impacts of waterfowl feeding on yield loss because of other sources of variation. However, less damage has been documented from winter grazing compared to spring grazing and yield loss after spring grazing on grassland appears more pronounced than losses on cereal fields. Although yield losses at national scales are trivial, individual farmers in areas of greatest waterfowl feeding concentrations suffer disproportionately, necessitating improved solutions to conflict. Accordingly, we review the efficacy of population management, disturbance, provision of alternative feeding areas, compensation and large-scale stakeholder involvement and co-management as options for resolving conflict based on the existing literature and present a framework of management advice for the future. We conclude with an assessment of the research needs fo...

Impact of hunting along the migration corridor of pink‐footed geeseAnser brachyrhynchus– implications for sustainable harvest management

“…As a consequence, hunting may be an important tool to manage populations as a means to alleviate conflicts with farmers and reduce the degradation of natural habitats (Pedersen, Speed & Tombre ; Koons, Rockwell & Aubry ; Fox et al . ). The efficiency of hunting as a management tool can be hard to evaluate, but it is strictly dependent on proper harvest monitoring and a flexible and adaptive harvest strategy.…”

Relating national levels of crop damage to the abundance of large grazing birds: Implications for management

“…Knowledge about the relationship between population size and damage levels is crucial for wildlife damage management (Conover, ; Madsen et al, ). However, this knowledge is lacking for large grazing birds, especially at large spatial scales (Fox et al, ), and the relationship is often assumed to be linear (Cusack et al, ; McKenzie & Shaw, ). In this manuscript we investigated this important knowledge gap in the ecology of wildlife damage management.…”

“…The need for interventions to mitigate damage by large grazing birds (geese, swans and cranes) on agricultural fields, has recently been accentuated (Fox & Madsen, ). Many populations of large grazing birds have increased from threatened to superabundant in Europe during at least five decades (Fox & Madsen, ) due to conservation efforts and agricultural intensification (Ebbinge, ; Fox, Elmberg, Tombre, & Hessel, ; Gauthier, Giroux, Reed, Bechet, & Belanger, ) and a warmer climate (Jensen, Madsen, Johnson, & Tamstorf, ; Mason, Keane, Redpath, & Bunnefeld, ). The increasing numbers of large grazing birds and their preference for agricultural fields over their natural foraging habitats – because crops provide higher quality food (Fox & Abraham, ) – cause a loss in harvest yield for the farmers (Fox et al, ).…”

“…For instance, plants may compensate for grazing (Van der Graaf, Stahl, & Bakker, ; McNaughton, ) and under certain conditions intermediate grazing may stimulate plant growth (McNaughton, ). Few studies have been able to evaluate the relationship between bird numbers and damage levels and this link has often simply been assumed to be linear (Cusack et al, ; McKenzie & Shaw, ), especially at the national scale where most political and strategic management decisions are conducted (Fox et al, ).…”

“…All states along the flyway for these birds need to reach a consensus in agreeing their goals and measures to tackle this issue (Madsen et al, ; Stroud et al, ). Several measures to mitigate the damage and conservation conflicts exist and have been suggested within the plans for example, set‐aside areas, bird‐scaring and population control (Fox et al, ). However, the current lack of data linking crop damage with population size creates a challenge when it comes to (a) predicting outcomes of proposed interventions, (b) allocating money for compensation costs and (c) adapt any subsequent goals and recommendations for monitoring and compensation strategies.…”