I recently learned a new phrase: "herby-kerby," which is regionalism from the Kalamazoo, MI area for a wheeled trash bin placed at the curb for trash collection. I've found several uses of the phrase:
In planning commission minutes for a nearby township:
"Mr. Hill also said the Best Way Disposal was going to supply one Herby-Kerby for each office site, which meant that there would be four Herby-Kerbies within the garbage enclosure."
In a blog post by someone from Kalamazoo:
As long as the bed gets made, the checkbook is balanced, the muffin tin is clean and the Herby Kerby is wheeled to the curb before 7am on Friday, how important is it in the long run to disagree about how it got done?
This regionalism is probably from a product name: Herby Curby.
Since encountering "herby kerby," I've also seen "herky-jerky," which Merriam Webster defines as "not smooth or graceful : marked by sudden movements or changes."
Then there's herp-derp, or harp-darp, defined at knowyourmeme.com.
Finally (or not? perhaps there are more?), there's hurdy-gurdy, the musical instrument. The Online Etymology Dictionary suggests this term may have originated from another reduplicative phrase, "hirdy-girdy," meaning "confusion or uproar," dating back to c. 1500.
As a speech-language pathologist, I see the phonological process of reduplication in young children's speech, but the entire syllable is reduplicated, without changing the initial consonant to "h:"
Billy says "baba" when he wants his bottle.
The phrases I've commented on above have two things in common: they all have a reduplicative rhyming word starting with "h" in the first position, and they all have either -er or an r-colored vowel as the syllable nucleus.
Does anyone know (1) why there are so many reduplicative phrases where the first word starts with "h," and (2) whether there examples without "r" in the syllable nucleus? Is there some reason behind these patterns, or am I just noticing a meaningless pattern?
EDIT: User Peter Shor commented on some without the "r:" hankdy-panky, hocus-pocus, higgledy-piggledy, hodge podge. Then there's also "helter-skelter." So I suppose the second point in the paragraph above is unneeded.
Best Answer
Other people have noticed this pattern. It doesn't seem to require an /r/ or an r-colored vowel (as you've already concluded). Shanthi Nadarajan, in "A Crosslinguistic Study of Reduplication," notes two common patterns of partial reduplication with replacement of onset consonants in English words: "h-C" and "C-w".
For "h-C", Nadarajan mentions the following examples "handy dandy", "hoity-toity". For "C-w", two examples are "bow wow" and "teeny weeny." But as others have mentioned in the comments, there are other partially reduplicated words that have other consonant alternations.
Interestingly, there also seem to be examples of reduplicated words in Malay that follow this pattern, but I don't know if that's just a coincidence. Nadarajan mentions that hina dina is Malay for "commoners" and hingar bingar is Malay for "pandemonium". Hina dina seems to be derived from the word dina "poor."
Apparently, Nils Thuns also studied reduplication in English and noticed this pattern. I found a brief description of his findings on the following web page: Slang Phonology, by Urs Dürmüller.
Why it exists
I found the following paper that attempts to explain this pattern: "The Effects of Production and Perception in the English Partial Reduplication", by Seokhan Kang, 2009 (PDF download).
Kang argues that "partial reduplication is motivated by only one principle: maximize the difference of the perceptual cues. More precisely, rhyme reduplication is motivated by the difference in temporal cues of [noise] and [transition]" (154; 2 in the PDF).
I don't fully understand Kang's argument, but he seems to say that the strong aspiration of /h/ generally enhances a perceptual contrast between the onset of the first and second element of the reduplicated phrase (157; 5 in the PDF). He suggests this contrast might be preferred due to something like the Obligatory Contour Principle (164; 12 in the PDF).
Kang also lists some similar examples from other languages.