Ecological implications of reduced forage quality on growth and survival of sympatric geese

Abstract

Summary1. Allometric constraints associated with digesting leaves require relatively small avian herbivores to consume high-quality forage. How such constraints are overcome during ontogeny when energy and nutrient requirements are relatively high has not been adequately explored. 2. We compared growth trajectories of Canada and lesser snow goose goslings raised on grass-based diets that differed in protein (10%, 14% or 18%) and fibre (30% or 45%) with those of free-living goslings on Akimiski Island, Canada. This common-garden experiment allowed us to test the hypotheses that (i) smaller-bodied geese are more negatively affected by reduced forage quality than larger-bodied geese, and (ii) goslings from subarctic brood-rearing areas have a limited capacity to slow growth in response to reduced forage quality. 3. Canada goose goslings fed low-protein (10%) diets were on average 44% lighter in body mass, had slower growth rates and were delayed >20 days in reaching 90% of asymptotic size compared with Canada goose goslings fed 18% protein. In contrast, snow goose goslings were unable to survive on the low-protein diets, and those fed high-or medium-protein diets grew at a similar rate and achieved similar asymptotic size. Canada and snow goose goslings fed low-protein diets had reduced growth rates of the tarsus and delayed emergence of the 9th primary. 4. Free-ranging Canada goslings on Akimiski Island were similar in mass and structural size to captive-reared goslings fed low-protein diets. In contrast, snow goslings were similar in mass and structural size to the captive-reared goslings fed the high-and medium-protein diets. This suggests that degraded habitats with mostly low-protein forage may be able to support Canada goslings better than snow goslings which require higher-quality forage to survive. 5. Size-related differences in gosling growth and survival in response to diminished diet quality may influence population size when available food reaches a lower threshold in protein content. However, goslings can avoid such density-dependent population regulation if they are able to move their broods and find adequate quality and quantity of forage.

Trophic mismatch and its effects on the growth of young in an Arctic herbivore

“…they do not digest plant fiber) and have a low nitrogen retention rate (Mattocks, ; Sedinger, ). Growing goslings, which must synthesize a large amount of new tissues, depend on food with high nitrogen concentration to meet their protein requirement as they cannot compensate a reduction in nitrogen concentration by increasing food intake (Sedinger, ; Richman et al ., ).…”

Forage plants of an Arctic‐nesting herbivore show larger warming response in breeding than wintering grounds, potentially disrupting migration phenology

“…This can be problematic for small goslings, which cannot access tall grass swards and need short, nitrogen‐rich grass for rapid growth after hatching (Doiron et al., 2014; Richman et al., 2015). In the breeding grounds of barnacle geese, climate warming is expected to result in a shorter “food peak” during which this high‐quality forage is available.…”

Nesting by Canada Geese on Baffin Island, Nunavut

“…The Canada Geese that we observed hatched on 18 July, which suggests that goslings would not have fledged until around 20 September, assuming a 63-day fledging period (captive Canada Geese fed high-quality diets ad libitum required 70 days to complete growth of primaries; Richman et al, 2015). Ground frosts began on northern Baffin Island in mid-August, and daily mean temperatures fell below freezing after 5 September 2013 (Fig.…”