The response to eye-like shapes by birds II. The importance of staring,pairedness and shape

Laboratory-reared 37-day-old white leghorn chicks were placed individually in an arena with one of a range of eight three-dimensional stimuli. The chick's behaviour was recorded over a 3-min period. Each bird was exposed to a stimulus which varied in three ways, being either circular concentric (eye-like) or rectangular, single or paired and which appeared to either persistently look at (track) or look away from (avoid) the chick. All three manipulations produced significant effects on how close the bird approached. The most avoided combination was two, tracking, eyelike shapes. The results are discussed in the context of the problems involved in isolating the effective components of stares and the head forwards threat posture.     

The response to eye-like shapes by birds. I. The effect of context: A predator and a strange bird

Laboratory-reared 40-day-old white leghorn chicks were placed individually in an arena with a dummy bird. The dummy was either a predator (kestrel) or a strange, non-predatory species (kiwi), further distinguished by the conspicuousness of the eye region. The hawk's eyes were either left intact (conspicuous) or covered. The kiwi's eyes were untouched (inconspicuous) or accentuated. Birds approached the unaltered kiwi but strongly avoided the hawk. Obscuring the eyes diminished hawk avoidance. Enhancement increased aversion to the kiwi. These results indicate the potential importance of the eyes as a stimulus feature of non-conspecifics.     

Calcium-related disorders in plants — a possible explanation for the effect of weather

Summary Incidence in the field of crop disorders known to be due to localised calcium deficiency bears little relation to soil calcium status, and is more often associated with particular types of weather. We are suggesting that brief periods of soil partial anaerobiosis following wet weather, and other unfavourable soil physical conditions such as compaction, lead to a temporary reduction in the distal, undifferentiated region of roots from which the majority of the calcium taken up is transported to the shoot. This might lead to a transient calcium deficiency in rapidly growing shoot tissues, and thence to necrosis.     

Fall in nutrient demand per unit root length during the linear phase of plant growth

If root length increases in proportion to plant weight, growth is expolinear, and plant composition is constant, then there is fundamental drop in nutrient demand per unit root length during the linear growth phase. This is in contrast to the exponential phase, when increments of growth and hence of nutrient demand are proportional to plant size and thus to root length: in the linear growth phase, they are constant despite increasing root length. For nutrient uptake models in which demand is based on growth and uptake is based on root length, this would suggest a tendency for nutrients to accumulate in the plant as it grows.