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

Abstract

Background: The ideal habitat use of waterbirds can be considered to be fixed, but current habitat use depends on environmental conditions, especially those of food characteristics, considered crucial to their use of habitats. Understanding how waterbirds respond to variation in food availability at degraded wetland sites and change their habitat use patterns over spatial and temporal scales should direct future conservation planning. The objectives of this study were to identify these spatial-temporal foraging habitat use patterns of Hooded Cranes (Grus monacha) and their relationship with food characteristics in the severely degraded wetlands of the Shengjin and Caizi lakes along with the Yangtze River floodplain. Methods: We investigated the changes in food characteristics, relative abundance and density of Hooded Cranes in various habitat types across three winter periods from November 2012 to April 2013. We examined the effect of these winter periods and habitat types on the pattern of use by the cranes and explored the relationship between these patterns and food characteristics using linear regression. Results: The food characteristics and habitat use clearly changed over spatial-temporal scales. In the early and mid-winter periods, the most abundant, accessible and frequented food resources were found in paddy fields, while in the late period the more abundant food were available in meadows, which then replaced the paddy fields. There were fewer effects of winter periods, habitat types and their interactions on habitat use patterns except for the effect of habitat types on the relative abundance, determined as a function of food abundance, but independent of food depth and sediment permeability. Conclusions: In response to the degradation and loss of lake wetlands, the cranes shifted their habitat use patterns by making tradeoffs between food abundance and accessibility over spatial-temporal scales that facilitated their survival in the mosaic of these lake wetlands.

Shifts in foraging behavior of wintering Hooded Cranes (Grus monacha) in three different habitats at Shengjin Lake, China

“…The collapse of submerged plants in lakes, the shrinking number of tubers of Vallisneria spiralis and their fragmented distribution have a detrimental effect on the distribution and foraging behavior of Hooded Cranes (Fox et al 2011). As the capacity of their natural habitat decreases, the cranes have shown flexible foraging strategies, by transferring to fallow paddy fields to forage and to supplement their food sources (Zheng et al 2015).…”

“…With wetland degradation and the loss of suitable habitats, the number and species of large submerged vascular plants are reduced and birds adjust their behavior to adapt to this change. Reductions in food availability force animals to move to habitats with higher food densities, such as paddy fields (Zheng et al 2015). Changes in food availability directly affect the foraging effort of waterbirds (Tome 1988).…”

“…Focal samplings were carried out using binoculars (8×) or a telescope (20-60×). We defined November and December as the early wintering period; January and February of the following year as the mid-wintering period and March and early April as the late wintering period (Zheng et al 2015). At the start of each focal observation, the location, date, time of day (morning, noon, afternoon), habitat type (meadows, mudflats, paddy fields), winter stage (early winter, midwinter, or late winter), age (adult or juvenile) and family size (including 0, 1 or 2 juveniles) were recorded.…”

“…Our cranes mainly exploit Anodonta woodiana, mollus and small amounts of tubers of wetland vegetation from the bare substrate of the lake bottom in the mudflats. Potentilla supina, Ranunculus polii and Polygonum criopolitanum with high digestibility were obtained from meadows and rice grains (Olyza sativa) from paddy fields (Zheng et al 2015). To investigate food density, we sampled the plots three times, i.e., at the arrival of the cranes at the lake (during the fall from 23 September to 17 October 2014), in the middle of the winter (from 5 to 25 January 2015) and at the departure of the cranes from Shengjin Lake (in the spring from 1 to 12 April 2015).…”

Effect of water level fluctuations on temporal-spatial patterns of foraging activities by the wintering Hooded Crane (Grus monacha)

“…Fluctuating water levels change the area of the exposed habitats as well as the soil hardness, which causes changes in food availability [59]. Accordingly, cranes adjust their foraging time budget to different water levels, responding to the changes in food resource abundance and availability and thus gain a greater energy intake with relatively less effort [60]. The foraging frequency of cranes was affected by the various types of food and interference in different habitats.…”