Hassall Mark, Riddington Roger, Helden Alvin
School of Environmental Sciences, University of East Anglia, NR4 7TJ, Norwich, UK.
Oecologia. 2001 Mar;127(1):97-104. doi: 10.1007/s004420000563. Epub 2001 Mar 1.
Feeding behaviour and preferences of brent geese, Branta b. bernicla were observed on pastures of different sward lengths and nitrogen contents. On swards of 2.0-6.0 cm captive geese took larger bites and had a higher intake rate when feeding on 6-cm swards than when feeding on shorter ones. In the field wild geese chose 6-cm swards in preference to both shorter and longer ones. For unfertilized pastures there was a strong negative relationship between nitrogen content and sward height: 11-cm swards contained 2.8% nitrogen, 3.5-cm swards 4.2% nitrogen. Application of 75 kg N ha organically based fertilizer at the end of October eliminated this relationship between nitrogen content and sward height, swards of all heights then having a mean content of 4.1% N. On fertilized plots the geese preferred swards longer than 6 cm with no indication of a decrease in preference up to the maximum height investigated, 16 cm. Breaking strain of grass laminae was measured to give an indication of the proportion of strengthening tissues in the leaves and hence their digestibility. Apical laminae from longer swards had a higher breaking strain than those from shorter swards. Unfertilized swards had a higher breaking strain than fertilized swards but the difference in breaking strain between long and short swards was the same on fertilized and control treatments. These results are discussed in relation to the forage maturation hypothesis and are interpreted as indicating that the primary constraint on maximizing energy intake rates is not the reduced energy digestibility of older foliage but the reduced nitrogen content in the higher-biomass swards. We conclude that it is the balance between maximizing energy intake and nitrogen absorption rates which results in the observed preference for intermediate-height swards.
在不同草皮长度和氮含量的牧场上观察了黑雁（Branta b. bernicla）的取食行为和偏好。在2.0 - 6.0厘米的草皮上，圈养的黑雁在取食6厘米草皮时比取食较短草皮时咬的口更大且采食率更高。在野外，大雁更喜欢6厘米的草皮，而不是更短或更长的草皮。对于未施肥的牧场，氮含量与草皮高度之间存在很强的负相关关系：11厘米的草皮含氮2.8%，3.5厘米的草皮含氮4.2%。10月底施用75千克/公顷的有机基肥消除了氮含量与草皮高度之间的这种关系，所有高度的草皮此时的平均含氮量为4.1%。在施肥的地块上，大雁更喜欢长度超过6厘米的草皮，在所研究的最大高度16厘米处，偏好没有下降的迹象。测量了草叶的断裂应变，以表明叶片中强化组织的比例，从而表明其消化率。较长草皮的顶端叶片比较短草皮的顶端叶片具有更高的断裂应变。未施肥的草皮比施肥的草皮具有更高的断裂应变，但在施肥和对照处理中，长草皮和短草皮之间的断裂应变差异相同。结合饲料成熟假说对这些结果进行了讨论，并解释为表明最大化能量摄入率的主要限制不是老叶能量消化率的降低，而是高生物量草皮中氮含量的降低。我们得出结论，正是在最大化能量摄入和氮吸收速率之间的平衡导致了观察到的对中等高度草皮的偏好。
