鄱阳湖区稻田生境中灰鹤越冬行为的时间分配与觅食行为

2013年11月—2014年2月,采用瞬时扫描和焦点动物法研究了鄱阳湖区稻田生境中灰鹤越冬行为的时间分配、活动节律与觅食行为。结果显示,觅食(64.09%)行为所占比例最大,其次为警戒(15.97%)、飞行(8.67%)和修整(7.37%)行为。4种主要行为中,觅食行为时间分配随越冬前期(11月)、中期(12月—翌年1月)、后期(2月)逐渐增加,其余行为时间均逐渐减少。各环境因子对主要行为的影响存在显著交互效应,修整行为随各环境因子变化最为明显,日最低温度升高、日最高温度降低、日照长度增加及湿度降低都会使修整行为增加;日照长度增加和湿度降低时,觅食行为增加;日照长度增加时,警戒行为减少。环境因子对成鹤影响效果与总体相同。环境因子仅对幼鹤的觅食行为影响显著,即日照长度增加和湿度降低,幼鹤觅食行为增加。环境因子对行为的影响为非线性关系,致使其影响趋势在不同范围内有所变化。行为节律上,灰鹤昼间各时段觅食行为保持较高水平,觅食高峰出现在11:00—11:59和17:00—17:30。灰鹤觅食生境与其夜宿地分离,致其上午觅食高峰有所推后。幼鹤昼间各时段行为节律与成鹤有较大差异,且各时段觅食行为比例均高于成鹤。灰鹤越冬期在稻田生境的平均啄食频率为(32.06±0.47)次/min,平均步行频率为(6.55±0.35)步/min。啄食频率与步行频率呈极显著负相关。时段和集群类型对啄食频率的影响存在显著交互效应。稻田中食物资源的可利用性逐渐下降,灰鹤的啄食频率随时间逐渐降低,为保证越冬期间获取足够的能量供应,灰鹤采取逐渐增加步行频率和觅食时间的策略。有觅食间隔的抽样单元中,平均警戒次数为(1.37±0.04)次/单元,平均警戒持续时间为(6.02±0.37)s/单元。成鹤花费在警戒的时间多于幼鹤,家庭群中的个体警戒持续时间多于聚集群中的个体。

Time budget and foraging behavior of wintering common cranes inhabiting rice fields of Poyang Lake

The common crane Grus grus is currently listed in the Second Category of National Key Protected Wildlife Species in China and the second appendix of CITES with a global population size estimated at 360000-370000 individuals. In China there is a wintering population of 10000-12000 individuals, of which 8408 individuals are found at Poyang Lake, which represents an important wintering habitat for the species in China. From November 2013 to February 2014, the wintering time budget and foraging behavior of common cranes inhabiting rice fields of Poyang Lake were observed by instantaneous scan and animal focal sampling methods. Common cranes spent most of their time foraging (64.09%), followed by alerting (15.97%), flying (8.67%) and maintenance (7.37%) behaviors. While foraging behavior increased over early, middle and late wintering stages, the other behaviors gradually declined over the same time period. There was a significant interaction effect among environmental factors on behaviors. Maintenance behavior changed most obviously with environmental factors. For example, an increase in maintenance was observed when daily minimum temperature increased, daily maximum temperature decreased, day length increased and humidity decreased. Foraging behavior increased when day length increased and humidity decreased; and alerting behavior increased when day length increased and humidity decreased. The effect of environmental factors on adult individuals was the same as the overall pattern. There was only one significant impact on the foraging behavior of juveniles. In other words, when day length increased and humidity decreased, the foraging behavior of juveniles increased. The impact of environmental factors on behavior may be a nonlinear relationship that results in the influence trends changing in different ranges. In terms of the activity rhythms, foraging behavior was always kept at a high level in each daytime period, peaking at 11:00-11:59 and 17:00-17:30. Because the foraging habitat and communal roosting habitat of common cranes were separated, the foraging peak in the morning was delayed. There was also a large difference in activity rhythms between adults and juveniles, with foraging behavior of juveniles being higher than adults in each observation period. Mean peck rate was (32.06± 0.47) pecks/min, mean step rate was (6.55± 0.35) steps/min, and there was a significant negative correlation between peck rate and step rate. A significant interaction effect between time and group types was found on peck rate. Because the availability of food resources in rice-field habitats decreases gradually over winter, the peck rate of cranes should also decrease gradually over time. To ensure adequate energy supply during the winter, it is likely that common cranes would change their foraging strategy by increasing the step rate and foraging time. Nearly (1.37±0.04) times and (6.02±0.37) s per unit with interval were used for alerting. Adults spend more time alerting than do juveniles and spend more time alerting when in family groups than in flocks. This paper also provides scientific suggestions for the conservation of this species.