The effects of food abundance and disturbance on foraging flock patterns of the wintering Hooded Crane (Grus monacha)

Abstract

Background: Food abundance and availability affect flock patterns of foraging birds. Cost and risk tradeoffs are especially critical for flocks of wintering waterbirds foraging in lake wetlands. Waterbirds losing suitable habitats face insufficient food supplies and high levels of disturbance, affecting their foraging activities. Our objective was to study the effects of food abundance and disturbances on flock size and the structure of Hooded Crane flocks wintering at Shengjin Lake and, as well, to understand the response of wintering waterbirds to habitat degradation for future management decisions and protection of the population. Methods: We investigated food abundance, disturbances and flock foraging activities of the wintering Hooded Crane in several foraging habitats of Shengjin Lake from November 2013 to April 2014. Flock size and structure were observed by scan sampling. Data on food abundance and disturbances were collected by sampling. Flock size and structure were compared among three wintering stages. The relationship between food resources, disturbances and flock size were illustrated using a generalized linear model. Results: In the early and middle wintering periods, the Hooded Crane used paddy fields as its major foraging habitat, where the number of foraging birds and flocks were the highest. During the late period, the cranes took to meadows as their major foraging habitat. The variation among foraging flock was mainly embodied in the size of the flocks, while the age composition of these flocks did not change perceptibly. Family flocks were notably different from flock groups in size and age composition. The results of a generalized linear model showed that the food abundance had a marked effect on foraging flock size and age composition, while disturbances had a significant effect only on flock size. From our analysis, it appeared that the combined effect of the two variables was significant on the size of the foraging flock, but had less impact on age composition.Conclusions: Food abundance and disturbances affected the flock size of the Hooded Crane. With abundant food and high disturbances, flock sizes increased owing to cooperation in foraging. To avoid competition and maximize foraging benefits, flock size reduces with an abundance of food but low disturbance. By trading off risks and costs, the cranes showed flexible flock distributions and a variety of foraging strategies to maximize benefits and to improve their fitness.

Significant Differences in the Gut Bacterial Communities of Hooded Crane (Grus monacha) in Different Seasons at a Stopover Site on the Flyway

“…However, in stopover site of Lindian, corn is the main food resource of hooded cranes [16,17]. It is known that food abundance and availability can influence the foraging strategies of hooded cranes, which may affect the physiology and ecology of their intestines [20]. Thus, the results suggested that variation in food resources and abundance may led to significant differences of bacterial community composition between the habitats.…”

“…Thus, the hooded cranes might have relatively higher food resource availability in fall compared to the spring. Food abundance dictates foraging efficiency and energy production [16,20], which might be a crucial factor influencing the foraging strategies of migratory birds. Dramatic shifts in bacterial community composition of hooded cranes might be associated with the different food abundances between the two periods.…”

“…The main food resources for hooded cranes are Vallisneria natans, Potamogeton malaianu, and rice grains [19]. In addition, the abundance and availability of food can influence the foraging strategies of the hooded crane, which may affect their intestinal physiology and ecology [20]. We hypothesized that: (a) as different habitats provide hooded cranes with different food resources, the diversity and the composition of their intestinal bacterial communities differ between stopover and wintering sites, and; (b) different seasons may offer hooded cranes with different food abundance at the same site, thus differences in the diversity and composition of the intestinal bacterial community between the spring and fall stopover sites may exist.…”

How do free-ranging domestic herbivores reduce competition within owner-determined herds?

“…In our study, the frequent splitting of herds into subherds, especially for large herds, in the dry season when food tends to be less abundant and of lower quality (Isvaran 2007;Yang et al 2015),…”

“…Thus, during these periods, it may be better for individuals to move in smaller groups. Wild, and freeranging domestic herbivores, have an advantage over herded domestic livestock, as they can change the size and structure of foraging groups in response to variation in resources (Yang et al 2015). For example, when the availability and quality of food declines, wild herbivores can reduce competition by temporarily or permanently splitting into smaller subgroups (Smith et al 2010).…”