I've done some Googling and only found case stories without any scientific backup. Most of the case reports about animal suicide online can by easily debunked by logical reasoning. For example there is a story about some dozen of cows throwing themselves off a cliff, but this event took place at the same moment a thunderstorm was growling, which could have easily spooked the poor animals to render them imprudently enough to make them less aware of the danger of the cliff(s) in the surrounding area.
Is there real scientific evidence about this phenomenon aside from a few case stories? Are there even scientific studies out there describing it or at least confirm that the reason for animal suicide in some of the case reports is inconclusive?
IMPORTANT EDIT: (in a response to Oddthinking♦'s remark about a lack of definition of suicide) Yes, definitions are a great problem here, I agree. What does count as suicide? A parent saving his or her child by taking a deadly bullet... is that suicide? It's all a matter of definitions. However, what I meant by suicide here is not (and this is a bit difficult to word correct for me, because I'm not fluent in English) the act of a direct response to a stimuli, either internal (need to reproduce) or external (seeing that child is in danger and sacrifice in an attempt to prevent the child's death), but rather the act of self destruction after analyzing and abstracting the stimuli and putting these ideas of ideas (e.g. if the idea is: I'm in pain because I get beaten every time, then an idea of that idea could be: this pain lowers my quality of life and in the absence of any hope that this regular beating will quit, committing suicide and facing the fear of death seems like a better option than continuing life). Note that this requires the animal to have concept of abstract concepts (in my wording ideas of ideas), like life, death, time, fear, etc. I originally wanted to ask this question because I was wondering about the fundamental difference between animals and humans (if any), and suicide seemed like a good candidate to presume investigating.
I hope I didn't confuse to much people :-)