Singing is a costly behaviour有误吗（2015年高考四川卷）

问题描述

下面一段选自2015年高考英语四川卷的阅读理解：
He told people at a conference, “There have been a couple of studies suggesting they are increasing their song output at night and during the day they are still singing. Singing is a costly behaviour and it takes energy. So by increasing their song output, there might be some costs of energy. ”

我对其中的Singing is a costly behaviour不理解，behaviour 不是不可数名词吗？它前面怎么可以用不定冠词呢？请专家老师解释和指导，非常感谢！

老师答疑

曾老师：

behaviour通常是用作不可数名词的，但有时也用作可数名词。请看《牛津高阶英语词典》上的解释：

【U, C】 the way a person, an animal, a plant, a chemical, etc. behaves or functions in a particular situation:

the behaviour of insects / dolphins / chromosomes ◆ studying human and animal behaviour ◆ (technical) to study learned behaviours and attitudes

▲ 再提供两个词典例句：

It is regarded as a natural behavior that a man helps the old down stairs. 帮助老人下楼被认为是理所当然的行为。《简明英汉词典》

These eating patterns are a learned behavior.这些进食模式是习得性行为。《柯林斯高级英汉双解学习词典》（第5版）

黎老师：

很多词典都把 behaviour 作不可数名词处理。作为学生，最好也把 behaviour 作不可数名词使用。但是，把 behaviour 作可数名词的例子也有，例如：
【U, C】the way a person, an animal, a plant, a chemical, etc. behaves or functions in a particular situation （人、动植物、化学品等的）表现方式，活动方式
（《牛津高阶英汉双解词典》第8版p.167）
以下例句摘自《柯林斯高级英汉双解学习词典》p.219, 2011年7月第1版：

You can refer to a typical and repeated way of behaving as a behaviour.
These eating patterns are a learned behavior. 这些进食模式是习得性行为。
It will be many years before anyone cao predict a hurricane's behavior with much accuracy. 要能够相当准确地预测出飓风的特性尚需多年。