There is tendency to make long titles, with redundant information inside. When a title has two lines it (usually) is bad for readability.
There is a reason why question has body - to provide the additional information there. And yes, inside the question one should make it precise, its worth to add an particular example, etc.
A bad thing is where there are redundant words (e.g. see also Isn't asking for 'research studies' in a question title redundant?). Even worse - when the question suggests answers or picks a lot of details that may be unrelated.
How about the following changes (or rather, a general rule of making titles as short as possible (but not shorter)):
- What transient factors, such as sleep deprivation or low mood, can affect performance on IQ tests?
-> What transient factors affect performance on IQ tests?
- Does caffeine improve performance for habituated consumers above pre-habituation levels?
-> Does caffeine improve performance for habituated consumers?
- Does the avian structure of many compact nuclei explain why crows are so capable of feats such as making tools?
-> Is the avian brain structure more efficient than the mammalian one?
(actually, I liked more the original title before the change)