Scaring waterfowl as a management tool: how much more do geese forage after disturbance?

More management, less damage? With increasing population size, economic costs of managing geese to minimize yield losses may outweigh benefits

Conflicts between farmers and geese are intensifying; yet, it remains unclear how interactions between goose population size and management regimes affect yield loss and economic costs. We investigate the cost-effectiveness of accommodation and scaring areas in relation to barnacle goose (Branta leucopsis) population size. We use an existing individual-based model of barnacle geese foraging in nature, accommodation, and scaring areas in Friesland, the Netherlands, to study the most cost-effective management under varying population sizes (i.e., between 20 and 200% of the current size). Our study shows that population size non-linearly affects yield loss costs and total costs per goose. The most cost-effective management scenario for intermediate to large populations is to avoid scaring of geese. For small populations, intensive scaring resulted in minimized yield loss costs and total costs, but also substantially lower goose body mass. Our results strongly suggest that scaring becomes a less effective management measure as goose populations increase.

Impact of disturbance on common scoter carrying capacity based on an energetic model

Shallow coastal zones are intensely used by humans but simultaneously are biodiversity hotspots, with a crucial role in the life cycle of many marine species. The competition for food or space between humans and protected wildlife intensifies under pressure of an increased need for marine resources for human consumption. For successful management it is important to establish the key components driving such conflicts of interest. Here we focus on the protected common scoter (Melanitta nigra), a sea duck wintering in coastal habitats that are rich in food, but also among the most disturbed marine systems worldwide. Due to the scoters' shyness disturbance impacts the birds' ability to forage and poses a conflict for balancing bird conservation and economics, including a fishery on its main bivalve prey Spisula subtruncata. In this study, we use an energy budget model to quantify the consequences of depth, currents and disturbance on scoter energetics and carrying capacity. Energetics were described using physical parameters and field data on food availability and disturbance. Results reveal non-linear relationships and a threshold value for when a scoter can no longer maintain its energy balance. This is caused by limited foraging time, rather than food availability. From a conservation perspective, this implies that a precautionary principle should be used, because there will be no warning when an area becomes unsuitable. In addition, the model was applied to study the effects of disturbance from different kinds of shipping in a coastal area of the North Sea, north of The Netherlands. Cargo shipping has the largest impact on the carrying capacity, where there is spatial overlap of prey and an intensively used shipping lane. In other prey distribution situations shrimp vessels may cause most disturbance. Spisula-Ensis fisheries did not limit the potential carrying capacity due to the limited catches and number of fishing trips. Scoter protection should be aimed at flexible spatial management and on only those vessel types above a Spisula bed with a large number of trips, and above all should work from a precautionary principle given the critical thresholds for scoter presence.

Nocturnal foraging lifts time constraints in winter for migratory geese but hardly speeds up fueling

Climate warming advances the optimal timing of breeding for many animals. For migrants to start breeding earlier, a concurrent advancement of migration is required, including premigratory fueling of energy reserves. We investigate whether barnacle geese are time constrained during premigratory fueling and whether there is potential to advance or shorten the fueling period to allow an earlier migratory departure. We equipped barnacle geese with GPS trackers and accelerometers to remotely record birds’ behavior, from which we calculated time budgets. We examined how time spent foraging was affected by the available time (during daylight and moonlit nights) and thermoregulation costs. We used an energetic model to assess onset and rates of fueling and whether geese can further advance fueling by extending foraging time. We show that, during winter, when facing higher thermoregulation costs, geese consistently foraged at night, especially during moonlit nights, in order to balance their energy budgets. In spring, birds made use of the increasing day length and gained body stores by foraging longer during the day, but birds stopped foraging extensively during the night. Our model indicates that, by continuing nighttime foraging throughout spring, geese may have some leeway to advance and increase fueling rate, potentially reaching departure body mass 4 days earlier. In light of rapid climatic changes on the breeding grounds, whether this advancement can be realized and whether it will be sufficient to prevent phenological mismatches remains to be determined.

COVID19-induced reduction in human disturbance enhances fattening of an overabundant goose species

Overabundant species can have major impacts on their habitat and induce trophic cascades within ecosystems. In North America, the overabundant greater snow goose (Anser caerulescens atlanticus) has been successfully controlled through special spring hunting regulations since 1999. Hunting is a source of mortality but also of disturbance, which affects the behavior and nutrient storage dynamics of staging snow geese. In 2020, the lockdown imposed by the COVID19 pandemic reduced hunting activity during their migratory stopover in Québec by at least 31%. This provided a unique opportunity to assess the effects of a sudden reduction in hunting disturbance on geese. We used long-term data on body mass combined with movement data from GPS-tracked birds in 2019 and 2020 to assess the effects of the 2020 lockdown on the spring body condition and behavior of greater snow geese. Body condition was higher in 2020 than in all years since the inception of spring hunting in 1999, except for 2019. However, in 2020 geese reached maximal body condition earlier during the staging period than in any other year and reduced by half time spent feeding in highly profitable but risky agricultural habitat in late spring compared to 2019. Although our study was not designed to evaluate the effects of the lockdown, the associated reduction in disturbance in 2020 supports the hypothesis that hunting-related disturbance negatively affects foraging efficiency and body condition in geese. Since spring body condition is related to subsequent breeding success, the lockdown could increase productivity in this overabundant population.

Less is more: On-board lossy compression of accelerometer data increases biologging capacity

GPS‐tracking devices have been used in combination with a wide range of additional sensors to study animal behaviour, physiology and interaction with their environment. Tri‐axial accelerometers allow researchers to remotely infer the behaviour of individuals, at all places and times. Collection of accelerometer data is relatively cheap in terms of energy usage, but the amount of raw data collected generally requires much storage space and is particularly demanding in terms of energy needed for data transmission.

Here, we propose compressing the raw accelerometer (ACC) data into summary statistics within the tracking device (before transmission) to reduce data size, as a means to overcome limitations in storage and energy capacity.

We explored this type of lossy data compression in the accelerometer data of tagged Bewick's swans Cygnus columbianus bewickii collected in spring 2017. Using software settings in which bouts of 2 s of both raw ACC data and summary statistics were collected in parallel but with different bout intervals to keep total data size comparable, we created the opportunity for a direct comparison of time budgets derived by the two data collection methods.

We found that the data compression in our case yielded a six times reduction in data size per bout, and concurrent, similar decreases in storage and energy use of the device. We show that with the same accuracy of the behavioural classification, the freed memory and energy of the device can be used to increase the monitoring effort, resulting in a more detailed representation of the individuals’ time budget. Rare and/or short behaviours, such as daily roost flights, were picked up significantly more when collecting summary statistics instead of raw ACC data (but note differences in sampling rate). Such level of detail can be of essential importance, for instance to make a reliable estimate of the energy budgets of individuals.

In conclusion, we argue that this type of lossy data compression can be a well‐considered choice in study situations where limitations in energy and storage space of the device pose a problem. Ultimately, these developments can allow for long‐term and nearly continuous remote monitoring of the behaviour of free‐ranging animals.

Water body type and group size affect the flight initiation distance of European waterbirds

Human encroachment on nature grows constantly, increasing human-wildlife interactions. Flight initiation distance (FID, the distance at which animals flee from an approaching threat) is often used to measure antipredator behaviour and establish buffer zones to reduce human impact on wildlife. In this study, we approached 10 waterbird species on larger lakes and narrower rivers using a motorboat. We investigated whether water body type, season (winter/spring), approach starting distance, species body mass, and group size influenced bird FID. Average bird FID was 145 ± 92 m and differed between species. In general, FID of all species was larger on lakes than rivers and increased with increasing group size and approach starting distance. When analysed separately for the two most common species, common goldeneyes (Bucephala clangula) and mallards (Anas platyrhynchos), FID increased with increasing starting distance on rivers, but not lakes, likely because birds on lakes have enough time to evaluate the approaching object and take flight at great distance. Additionally, birds might perform different activities on lakes versus rivers, leading to varying energetic trade-offs between the two habitat types, which may affect the decision when to take flight. Finally, mallards aggregated in larger groups on lakes, which affected FID, likely due to enhanced visibility (i.e., earlier detection of the approaching boat) and detection probability (via increased group size) on lakes. Our results emphasize the importance of accounting for habitat characteristics, such as water body type, when studying waterbird FID, because they can affect the visibility of stimuli, group size and potentially animal behaviour, factors which should be taken into account when planning buffer zones for waterbirds in conservation areas.

Cost-benefit analysis for invasive species control: the case of greater Canada goose Branta canadensis in Flanders (northern Belgium)

Background

Sound decisions on control actions for established invasive alien species (IAS) require information on ecological as well as socio-economic impact of the species and of its management. Cost-benefit analysis provides part of this information, yet has received relatively little attention in the scientific literature on IAS.

Methods

We apply a bio-economic model in a cost-benefit analysis framework to greater Canada goose Branta canadensis, an IAS with documented social, economic and ecological impacts in Flanders (northern Belgium). We compared a business as usual (BAU) scenario which involved non-coordinated hunting and egg destruction with an enhanced scenario based on a continuation of these activities but supplemented with coordinated capture of moulting birds. To assess population growth under the BAU scenario we fitted a logistic growth model to the observed pre-moult capture population. Projected damage costs included water eutrophication and damage to cultivated grasslands and were calculated for all scenarios. Management costs of the moult captures were based on a representative average of the actual cost of planning and executing moult captures.

Results

Comparing the scenarios with different capture rates, different costs for eutrophication and various discount rates, showed avoided damage costs were in the range of 21.15 M€ to 45.82 M€ under the moult capture scenario. The lowest value for the avoided costs applied to the scenario where we lowered the capture rate by 10%. The highest value occurred in the scenario where we lowered the real discount rate from 4% to 2.5%.

Discussion

The reduction in damage costs always outweighed the additional management costs of moult captures. Therefore, additional coordinated moult captures could be applied to limit the negative economic impact of greater Canada goose at a regional scale. We further discuss the strengths and weaknesses of our approach and its potential application to other IAS.

Responses of wintering geese to the designation of goose foraging areas in The Netherlands

The Netherlands is important for wintering migratory herbivorous geese, numbers of which have rapidly increased, leading to conflict with agriculture. In 2005/2006, a new goose management policy aimed to limit compensation payments to farmers by concentrating foraging geese in 80 000 ha of designated 'go' areas-where farmers received payment to accommodate them-and scaring geese from 'no go' areas elsewhere. Monthly national counts of four abundant goose species during 10 years prior to the new policy and in 8 years following implementation found that 57% of all goose days were spent within 'go' areas under the new management, the same as prior to implementation. Such lack of response suggests no predicted learning effects, perhaps because of (i) increases in abundance outside of 'go' areas, (ii) irregularly shaped boundaries and enclaves of 'no go' farmland within 'go' areas and/or (iii) insufficient differences in disturbance levels within and outside designated areas.

Why geese benefit from the transition from natural vegetation to agriculture

The energy and nutrient content of most agricultural crops are as good as or superior to natural foods for wild geese and they tend to be available in agricultural landscapes in far greater abundance. Artificial grasslands (fertilised native swards and intensively managed reseeds) offer far superior quality forage and higher intake rates than seminatural or natural grasslands. The availability of such abundant artificial food explains the abandonment of traditional habitats for farmland by geese over the last 50-100 years and favours no reduction in current levels of exploitation of agriculture. Continental scale spatial and temporal shifts among geese undergoing spring fattening confirm their flexibility to respond rapidly to broadscale changes in agriculture. These dramatic changes support the hypothesis that use of agricultural landscapes has contributed to elevated reproductive success and that European and North American farmland currently provides unrestricted winter carrying capacity for goose populations formerly limited by wetlands habitats prior to the agrarian revolution of the last century.