Agricultural pastures challenge the attractiveness of natural saltmarsh for a migratory goose

Abstract

Abstract1. Broad-scale land conversions and fertilizer use have dramatically altered the available staging area for herbivorous long-distance migrants. Instead of natural land, these birds rely increasingly on pastures for migratory fuelling and stopover, often conflicting with farming practices. To predict and manage birds' future habitat use, the relative advantages and disadvantages of natural (e.g. saltmarsh, intertidal) versus anthropogenic staging sites for foraging need to be understood.2. We compared the migratory staging of brent geese on saltmarsh and pasture sites in spring. Food quality (nitrogen and fibre content), antagonistic behaviour, and body weight were quantified at nearby sites in simultaneous seasons. Individuals were tracked with high-resolution GPS and accelerometers to compare timing of migration and time budgets during fuelling.3. On pastures, birds rested more and experienced higher ingestion rates, similar or superior food quality and reduced antagonistic interactions than on saltmarsh.4. Brent geese using fertilized grasslands advanced their fuelling and migration schedules compared to those using saltmarsh. Pasture birds reached heavy weights earlier, departed sooner, and arrived in the Arctic earlier.5. Intertidal mudflats were frequently visited by saltmarsh birds during the day, and available food there (algae, some seagrass) was of higher quality than terrestrial resources. Availability of intertidal resources was an important factor balancing the otherwise more favourable conditions on pastures relative to saltmarsh.6. Synthesis and applications. Disadvantages of longer foraging effort, more antagonistic interactions and delayed fuelling schedules on traditional saltmarshes may cause geese to exchange this traditional niche in favour of pastures, especially in a warming climate that requires advancement of migratory schedules. However, due to its high quality, intertidal forage can complement terrestrial foraging, potentially removing the incentive for habitat switches to pastures. The relatively high quality of green algae and seagrass, and birds' remarkable preference for these resources when available, provides a key for managers to create landscapes that can sustain this special- | INTRODUC TI ONHuman activity is altering our planet's surface in rapid and pervasive ways. Over 80% of the earth's land mass is now under direct human influence (Sanderson et al., 2002), with croplands and pastures occupying over 40% of the total area (Asner, Elmore, Olander, Martin, & Harris, 2004;Foley, 2005). Migratory birds need to navigate these humanaltered landscapes during their seasonal migration and depend on them as alternatives to lost natural habitat. Especially, agricultural land plays an important role in supporting migratory bird communities year-round:pastures provide wintering and breeding grounds to meadow passerines, waterfowl and waders (Knopf, 1994); rice fields (Elphick, 2015;Lourenço, Mandema, Hooijmeijer, Granadeiro, & Piersma, 2010) (Abraham, Jefferies, & Alisauskas, ...

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

“…and 'inactive' (Dokter et al, 2018). Although this yielded interesting results in combination with the GPS data of the same tags, more ACC measurements could have increased the understanding of the behavioural patterns of these geese in their fuelling and migration periods.…”

“…One example of lossy data collection is a conditional sampling regime, where the frequency of sampling is not continuously the same. The exact frequency of sampling can then, for example, be determined by the researcher (Bouten et al, 2013), based on the energy level of the device (Dokter et al, 2018; see Appendix A), or the inferred behaviour of the focal animal (e.g. flight detection, based on GPSground speed [Harel, Horvitz, & Nathan, 2016] or the overall activity level [Brown et al, 2012]).…”

Ontogenetic niche shifts as a driver of seasonal migration

“…Arctic foxes, Taimyr gulls and snowy owls, even though the exact predation pressure depends on the lemming cycle (Summers 1986;Ebbinge and Spaans 2002;de Fouw et al 2016). In its coastal temperate non-breeding range, brent geese utilize different habitats, ranging from seagrass beds to lower salt marshes to coastal agricultural fields (Dokter et al 2018). Especially adult brent geese, with active salt glands, profit from the saline conditions, which provide high-quality salt marsh plants, seagrasses (Zostera spp.)…”

Wintering Geese Trade-Off Energetic Gains and Costs When Switching from Agricultural to Natural Habitats

“…Barnacle Geese grazing in salt marshes achieved lower intake rates of protein and fat, but the difference was only slight. An increase in grazing to make up for lower food quality has been observed for Brent Geese Branta bernicla grazing in salt marshes (Dokter et al 2018b) and Pink-footed Geese, which spent 80% of their time grazing in pastures, but only 54% in newly sown barley fields where intake rates were higher (Madsen 1985). Due to the relatively low fibre content and high digestibility of food plants in pastures, geese can attain their daily energy requirements at a faster rate than in salt marshes (Fox et al 2016).…”

“…This suggests that geese which switch to salt marshes prior to migration do not suffer from potential protein deficiency. For Brent Geese, the timing of migration of birds primarily staging in salt marshes was delayed relative to birds staging in pastures, a difference which only disappeared close to arrival on the breeding grounds (Dokter et al 2018b). Geese may be able to compensate for smaller protein stores by additional feeding in salt marshes while staging or at stopover sites during migration (Prop & Spaans 2004).…”