Modelling behavioural and fitness consequences of disturbance for geese along their spring flyway

Abstract

Summary 1.For migratory birds the implications of environmental change may be difficult to predict because they use multiple sites during their annual cycle. Moreover, the migrants' use of these sites may be interdependent. Along the flyway of the Svalbard pinkfooted goose Anser brachyrhynchus population, Norwegian farmers use organized scaring to minimize goose use of their grasslands in spring. We assessed the consequences of this practice for regional site use of pink-footed geese along their spring migration route. 2. We used dynamic programming to find the sequence of migratory decisions that maximizes the fitness of female geese during spring migration, assuming scaring impinges on both food-intake rates and predation risk. The parameterization of the model was based on data gathered from individually marked pink-footed geese between 1991 and 2003. 3. The effect of scaring in terms of fitness and site use was most noticeable regarding food-intake rate. Scaring resulted in a redistribution of geese along the flyway. Furthermore, the outcomes of the modelling exercises were highly dependent on whether or not the geese were omniscient or naive: at moderate scaring levels naive geese were predicted to succumb. 4. On a qualitative basis there was good correspondence between the predictions from the model and the empirical evidence gathered to date. 5. Synthesis and applications . Besides highlighting the importance of learning and changing behaviour in an adaptive fashion, our modelling exercise indicated the potential vulnerability of the geese to abrupt environmental change. In addition, the exercise emphasized the interdependence of site use along the migratory flyway. The model supports the necessity for an integrated flyway management approach. In Norway, discussion is ongoing about the future management of the spring conflict between farming interests and geese. Farmers in north and mid-Norway have announced that they will expand the scaring campaign if a long-term solution, including a compensation scheme, is not forthcoming. If scaring on such a large scale is implemented abruptly, it may have severe consequences for the population: management of both the scaring intensity and its geographical extent is urgently required.

Ecophysiology of avian migration in the face of current global hazards

“…Modification of migratory and subsequent breeding schedules in attempts to match climate-change-driven changes in food availability along the flyway has been observed in geese and numerous passerine species; however, these adjustments in timing appear to be imperfect [111]. Although some theoretical modelling of optimal migration itineraries of birds in response to a changing environment indicate that migrants may theoretically be able to cope with substantial changes to their surroundings [112], this has only been partly confirmed by empirical data [113]. The outcome of those theoretical models may not appear surprising given the huge climatic changes that many of the current migratory avifauna experienced during the past ice ages.…”

“…However, it should be borne in mind that during those periods, some species experienced bottlenecks that almost led to their extinction [114]. Theoretical models also indicate that abrupt changes in environmental conditions may be too rapid for birds to cope with, unless transitions are in temporal synchrony with birds' ability to evolve or adapt to these changes [112]. Moreover, optimality models consider only what a bird should and should not do, and assume it has the mechanisms to make appropriate responses.…”

Manipulating individual state during migration provides evidence for carry-over effects modulated by environmental conditions

“…Geese are a suitable model because they depend in part on imported energy reserves to invest in egg production and incubation [16], and spring body condition is thought to be a key factor determining their reproductive output [16 -18]. Examples of previously documented COEs negatively affecting reproduction in geese include scaring off agricultural lands in pink-footed geese (Anser brachyrhynchus; [19]) and non-lethal effects of hunting [8] in greater snow geese (Anser caerulescens atlanticus; [3]). In the latter example, disturbance owing to a new spring hunt reduced feeding time, increased flying time and precluded access to some foraging areas, which reduced nutrient storage [20] and reproductive success [21].…”

Landscape structure, human disturbance and crop management affect foraging ground selection by migrating geese

“…The effect may be linked with two phenomena. Firstly, farmers and local inhabitants may directly disturb foraging birds around their properties due to normal human activity or by implementing scaring practices to protect crops Klaassen et al 2006;Jensen et al 2008). Secondly, there is an abundance of freely roaming dogs and cats in Polish villages.…”

“…In Poland, forest edges and small mid-field forests are a major habitat of the opportunistic Red Fox Vulpes vulpes (Tryjanowski et al 2002;Jankowiak et al 2008) are used as well by the White-tailed Eagle Haliaeetus albicilla that preys on geese (Roder et al 2008) and whose appearance causes entire goose flocks to take flight (personal observations). Other explanations for avoidance of forest edges is that hunters often hunt from hides at forest edges and forestry workers may occasionally work and appear at forest edges, thereby disturbing geese foraging nearby (Klaassen et al 2006).…”