Is there such thing as too many references for one paper?

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It's really a judgment call… some people consider that more references is good, because it gives the reader a wider perspective into the issue, and some people consider it a bad practice (in old times because it wasted paper, but nowadays mainly because it obscures the more valuable information inside a long wall of text).

I have, as a reviewer, sometimes asked authors to cut down on the number of references, so it is certainly an acceptable practice. Here are some factors you may consider when making the decision:

• Does each individual reference bring something to the paper, i.e. is used to back up a fact, idea, or to give credit for a specific (and relevant) new idea that it introduced?

• Are references cited in block? I tend to consider it is very bad practice:

  A series of recent experiments have shown systematically that current human-powered aircrafts are not suitable for mass transportation [refs. 9–21]

  Each paper (or group of two or three papers, at the very most) should be used with regards to a specific point in the discussion.

• Somewhat disguised form of the earlier: are long lists of claims and references justified? Sometimes many citations are used as “examples”, where a few would suffice.

• Could some of the citations be replaced by one or two reviews on the topic?

• Are the work cited really the seminal work on each topic/idea/experiment, or are there also less “worthy” works cited?

Finally, it is true that there are some unethical practices that can lead to inflated number of citations. Excessive self-citation is certainly one, but there are others. For example, some authors cite very widely papers from all groups in their field, even when it is not really warranted, in an effort to help their chances at peer review: the idea is that the reviewer is less likely to be harsh to a manuscript that cites 5 of her own papers.

And in conclusion, if you believe that self-citation was the motivation, there is nothing wrong with reporting your doubts to the editor.

I can only see one way to resolve this and that is to critically assess if all references are necessary. Self-citation can be a problem but it may be perfectly fine in situations where the author is a leader in, for example, a small field. Excessive citations can also be a sign of the author not being able to weed out the critical papers from the "mass". In some cases, it may be tempting to provide all the literature found on a particular topic wher perhaps a review paper or relatively new paper summarizing past work could be referenced using the form "(e.g. author, yyyy)", indicating it is one of several possible references on the topic. I think it is perfectly fair to ask for such changes if the excessive referencing is clearly just excessive.