Decadal declines in avian herbivore reproduction: density‐dependent nutrition and phenological mismatch in the Arctic

Abstract

A full understanding of population dynamics depends not only on estimation of mechanistic contributions of recruitment and survival, but also knowledge about the ecological processes that drive each of these vital rates. The process of recruitment in particular may be protracted over several years, and can depend on numerous ecological complexities until sexually mature adulthood is attained. We addressed long-term declines (23 breeding seasons, 1992-2014) in the per capita production of young by both Ross's Geese (Chen rossii) and Lesser Snow Geese (Chen caerulescens caerulescens) nesting at Karrak Lake in Canada's central Arctic. During this period, there was a contemporaneous increase from 0.4 to 1.1 million adults nesting at this colony. We evaluated whether (1) density-dependent nutritional deficiencies of pre-breeding females or (2) phenological mismatch between peak gosling hatch and peak forage quality, inferred from NDVI on the brood-rearing areas, may have been behind decadal declines in the per capita production of goslings. We found that, in years when pre-breeding females arrived to the nesting grounds with diminished nutrient reserves, the proportional composition of young during brood-rearing was reduced for both species. Furthermore, increased mismatch between peak gosling hatch and peak forage quality contributed additively to further declines in gosling production, in addition to declines caused by delayed nesting with associated subsequent negative effects on clutch size and nest success. The degree of mismatch increased over the course of our study because of advanced vegetation phenology without a corresponding advance in Goose nesting phenology. Vegetation phenology was significantly earlier in years with warm surface air temperatures measured in spring (i.e., 25 May-30 June). We suggest that both increased phenological mismatch and reduced nutritional condition of arriving females were behind declines in population-level recruitment, leading to the recent attenuation in population growth of Snow Geese.

Normalized Difference Vegetation Index as an Estimator for Abundance and Quality of Avian Herbivore Forage in Arctic Alaska

“…The timing of peak nitrogen concentration is an essential parameter for understanding reproductive success of arctic herbivores. Failure by an animal to adjust the timing of reproduction to match optimal availability of high quality food resources on breeding areas (i.e., "phenology mismatch") can lead to poor reproductive success [60][61][62], slower growth of young [61,63], and ultimately lower survival and recruitment [61,64,65]. The timing of peak nitrogen concentration in halophytic wetlands is not only important for assessing wildlife habitat quality, but is variable enough from year to year to require frequent monitoring.…”

Delayed herbivory by migratory geese increases summer‐long CO2 uptake in coastal western Alaska

“…These phenological mismatches may be even greater at high latitudes where many herbivores migrate in the spring from temperate regions and do not experience local cues that may minimize the difference in timing of biological events between trophic levels. Phenological mismatches have changed many populations (Doi, Gordo, & Katano, 2008;Doiron, Gauthier, & Levesque, 2015;Post & Forchhammer, 2008;Ross, Alisauskas, Douglas, & Kellett, 2017;Visser, Noordwijk, Tinbergen, & Lessells, 1998) but could also alter ecosystem function, as the timing of interactions between primary producers and consumers could affect ecosystem processes, such as greenhouse gas fluxes (Kelsey et al, 2018). Phenological mismatches have changed many populations (Doi, Gordo, & Katano, 2008;Doiron, Gauthier, & Levesque, 2015;Post & Forchhammer, 2008;Ross, Alisauskas, Douglas, & Kellett, 2017;Visser, Noordwijk, Tinbergen, & Lessells, 1998) but could also alter ecosystem function, as the timing of interactions between primary producers and consumers could affect ecosystem processes, such as greenhouse gas fluxes (Kelsey et al, 2018).…”

Density‐dependent and phenological mismatch effects on growth and survival in lesser snow and Ross's goslings

“…Adult survival during the breeding season can reasonably be assumed to be very nearly 1.0. Annual survival of arctic‐nesting snow goose adults was recently estimated as 0.899 (Calvert et al ), yielding a mean monthly survival of 0.99. Summer survival is higher than average since hunter harvest does not occur during the breeding period, and there are no records of severe mass mortality events due to disease as seen in other colonial arctic‐nesting species (e.g.…”

“…Quasi‐observational weather conditions were retrieved from the North American Regional Reanalysis (NARR) obtained through the National Oceanic and Atmospheric Administration National Operational Model Archive and Distribution System (NOMADS, <http://nomads.ncdc.noaa.gov/>). [see Ross et al () for reliability of NARR data in comparison with conditions measured by an automated weather station at Karrak Lake]. Adverse weather conditions after hatch can cause high mortality of precocial young [e.g.…”

“…Grazing pressure from high densities of foraging geese can depress productivity of principal forage plants (Jefferies , Kerbes et al 1990), and result in density‐dependent effects on life‐history traits (e.g. clutch size; Cooch et al ), growth (Larsson et al , Slattery ) and ultimately, population dynamics (Fondell et al , but see Hupp et al ).…”