Should edited, multi-author undergraduate textbooks have many in-text citations? Journal articles are packed with in-text citations of other works to validate points and situate the work in the context of past works. What about undergraduate textbooks with multiple chapter authors? Each chapter author is likely to be an expert in the field. Are citations necessary in this case as for any other academic work? Or do citations interrupt the smooth reading of the text for undergraduates? Or are they less necessary (or less numerous) because the authors are experts?

I'm editing a textbook and want to have some uniformity among the chapters regarding the need for citations and the number of citations. Each chapter will have a reference list.
My view is that in-text citations to relevant, pedagogical references are very useful.  Introduction to Electrodynamics by David J. Griffiths is an excellent example.


  Are citations necessary in this case as for any other academic work? 


Yes.  They are still an ethical obligation, but they might not be in-text.


  Or do citations interrupt the smooth reading of the text for undergraduates?


Obviously yes, but in my opinion that is unimportant.


  Or are they less necessary (or less numerous) because the authors are experts?


The identity of the author is irrelevant to the ethical obligation to cite prior work.