Habitat utilization and resource partitioning of wintering Hooded Cranes and three goose species at Shengjin Lake

Abstract

The loss and degradation of wetlands have adversely affected waterbirds, which depend on wetland habitats. Interspecific competition has an important effect on habitat utilization of wintering waterbirds. Resource utilization, including partitioning, in degraded wetlands has become a hot issue in ecological studies of wintering waterbirds. In order to have an insight into the habitat utilization and resource partitioning between a Hooded Crane (Grus monacha) population and the guild of three goose species, i.e., Anser fabalis, A. albifrons and A. erythropus wintering in lake wetlands, we carried out a study at Shengjin Lake National Nature Reserve from November 2011 to April 2012. We surveyed the Hooded Cranes and goose guild foraging in various habitats during the wintering periods with a combined method of fixed route searching and fixed site observations. Resource partitioning was studied by means of calculating habitat utilization rates and the width and overlap of spatial niches. The results showed that the habitat utilization rate and the width of spatial niches of the Hooded Crane population and goose guild shifted with the season. The habitat utilization rates of the cranes in grasslands were high at all three wintering stages. The habitat utilization rates were 0.454, 0.435 and 0.959 respectively for the Hooded Cranes and 0.627, 0.491 and 0.616 for the goose guild. This suggests that the overlap in grasslands was higher between cranes and goose guild. Most habitats were accessible at the middle stage, so the width of the spatial niche of the cranes (1.099) and goose guild (1.133) both reached their peak at this stage. The greatest niche overlap was 0.914 for these two groups at the late stage, followed by 0.906 at the middle stage and the smallest was 0.854 at the early stage. Ecological response to the changes in habitats of wintering waterbirds was clearly shown in the dynamic variations of the niche of both the Hooded Cranes and the three goose species. Coexistence among waterbirds was achieved by regulation of niche width to reduce niche overlap and relieve interspecific resource partitioning.

Effects of variation in food resources on foraging habitat use by wintering Hooded Cranes (Grus monacha)

“…Spatial-temporal fluctuations in food availability affect crane habitat use within the wetlands (Zhao et al 2013). For the purposes of our study, the wintering periods were separately analyzed.…”

“…Given that the length of the bill of cranes is approximately 15 cm and that cranes exhibit a variety of foraging techniques (Jia et al 2013), in each quadrat, we collected from each of these plots the tubers and roots of aquatic vegetation, such as those of Potentilla supine, Polygonum hydropiper, Ranunculus polii, Sagittaria sagittifolia, some other vegetable food items consumed by the Hooded Cranes (Zhao et al 2013), entrails of mollusks and rice grains, within the typical 15 cm foraging depth constraint for Grus species of the foraging sediment (not including water depth) (Wang 1988;Jia et al 2013). We dried these food items at 65°C in an oven (YHG-9050A; Derip, Suzhou, China) to a constant weight for ≥ 72 h, which represented their dry weight (g).…”

“…In these lake wetlands, Vallisneria natans, Potamogeton malaianus and mollusks are the main food resources for the Hooded Crane. Owing to the degradation and loss of these lake wetlands, the cranes have changed their dietary structure (Zhou et al 2010) and are declining in number (Harris et al 2000;Zhao et al 2013). Although some recent studies have revealed considerable flexibility in wader habitat use (Puglisi et al 2005;White et al 2006), including Grus species (Liu et al 2010;Li et al 2013), this flexibility of habitat use by larger migratory waders is regional and species-specific (Ma et al 2003;Aborn 2010;Liu et al 2010).…”

“…Variety in spatial and temporal food resources plays an important role in habitat use patterns of many avian species (Newton 1998;Ackerman et al 2006), adjusting their spatial behavior to complete their annual life history (Fox et al 1998;Link et al 2011;Zhao et al 2013). In winter, food availability may be a particular constraint on habitat use by birds (Marra and Holberton 1998;Wang et al 2013), because the food supply usually is at its lowest level (Moen 1976).…”

“…Lake wetlands, such as the middle and lower Yangtze River floodplains, form significant global networks (Chen et al 2011;Zhao et al 2013), containing abundant aquatic and biological resources and represent important wintering grounds supporting large numbers of wintering migratory waterbirds, including several endangered species Chen et al 2011). However, rising levels of human intervention and destruction over the last thirty years Fox et al 2011) are largely responsible for the increasing degeneration and loss of lake wetlands, resulting in the decline of suitable habitats for waterbirds in the Yangtze River floodplains (Zhou et al 2010;Jia et al 2013), possibly exerting far-reaching effects on the networks and services for waterbirds, which are experiencing dramatic changes in this ecosystem Chen et al 2011).…”