Contrasting consequences of climate change for migratory geese: Predation, density dependence and carryover effects offset benefits of high‐arctic warming

Abstract

Climate change is most rapid in the Arctic, posing both benefits and challenges for migratory herbivores. However, population‐dynamic responses to climate change are generally difficult to predict, due to concurrent changes in other trophic levels. Migratory species are also exposed to contrasting climate trends and density regimes over the annual cycle. Thus, determining how climate change impacts their population dynamics requires an understanding of how weather directly or indirectly (through trophic interactions and carryover effects) affects reproduction and survival across migratory stages, while accounting for density dependence. Here, we analyse the overall implications of climate change for a local non‐hunted population of high‐arctic Svalbard barnacle geese, Branta leucopsis, using 28 years of individual‐based data. By identifying the main drivers of reproductive stages (egg production, hatching and fledging) and age‐specific survival rates, we quantify their impact on population growth. Recent climate change in Svalbard enhanced egg production and hatching success through positive effects of advanced spring onset (snow melt) and warmer summers (i.e. earlier vegetation green‐up) respectively. Contrastingly, there was a strong temporal decline in fledging probability due to increased local abundance of the Arctic fox, the main predator. While weather during the non‐breeding season influenced geese through a positive effect of temperature (UK wintering grounds) on adult survival and a positive carryover effect of rainfall (spring stopover site in Norway) on egg production, these covariates showed no temporal trends. However, density‐dependent effects occurred throughout the annual cycle, and the steadily increasing total flyway population size caused negative trends in overwinter survival and carryover effects on egg production. The combination of density‐dependent processes and direct and indirect climate change effects across life history stages appeared to stabilize local population size. Our study emphasizes the need for holistic approaches when studying population‐dynamic responses to global change in migratory species.

High-Arctic family planning: earlier spring onset advances age at first reproduction in barnacle geese

“…Global warming is having profound effects on reproduction in Arctic geese and other Arctic herbivores [34,47]. Our results, from one of the most rapidly warming places on Earth [6], indicate that climate change is affecting key life-history traits like AFR.…”

“…However, they may, eventually, be unable to keep up with fast-changing spring conditions [51], leading to phenological mismatch in food-web interactions [52,53], with potentially negative reproductive consequences [54]. Nevertheless, this population shows no current indication of mismatch effects [34]. On the contrary, Arctic climate change appears to allow higher gosling production and earlier AFR, which may have positive consequences for population persistence.…”

“…In such cases, AFR is likely to change over time with long-term trends in breeding conditions. Spring phenology can affect AFR since it impacts both clutch success/size and hatching success, through effects on the timing of nesting and food availability during incubation [26,27,34]. Colder springs delay snowmelt, and therefore nest-site availability, but also the timing of food availability by delaying plant growth onset [34].…”

“…Accumulated winter snowfall [38] was included initially, but showed no evidence of an effect. SO is the (ordinal) day when the 10 day smoothed daily temperature crosses 0°C and remains above for at least 10 days [39] and has been shown to affect egg production [34]. POP is an annual estimate of adult numbers in the study population, which negatively affects gosling production and fledgling recruitment [34,40].…”

Management options for a resident Barnacle Goose (Branta leucopsis) population in Flanders. A comparison of different scenarios using population modelling

“…This can also be expected for non-migratory Barnacle Geese since the absence or decrease of migratory efforts, and associated high energy costs, can result in higher reproductive output as well as in higher adult, juvenile and offspring survival (Bromley & Jarvis 1993, van der Jeugd et al 2009. This is due to the fact that Arctic-nesting geese are generally classified as capital breeders, relying on stored energy levels and thus independent of nutritional intake during the pre-laying period (Ryder 1970, MacInnes & Dunn 1988, Bromley & Jarvis 1993, Layton-Matthews et al 2019). Therefore, reproductive success, reflected in laying date and clutch size, depends mainly on female pre-migration body condition, migratory behaviour and resulting energy reserves on arrival in the breeding area (Ankney & MacInnes 1978, Cooper 1978, Prop et al 1984, Lessels 1986, Alisauskas & Ankney 1990, Kostin & Mooij 1995, Prop & Black 1998, Bêty et al 2003, Prop et al 2003, Hübner 2006.…”