Closing this fork.

GG5 tags it as 【諺】 and most expressions tagged that way we have tagged as [proverb]. Probably many should be tagged as idioms, e.g. "浅瀬に仇波 （あさせにあだなみ） (exp) (proverb) deep rivers move in silence".
I'll raise an issue on the proverb/idiom tagging.
Should this one be glossed differently? I don't think so.

imidas example
「こんな会社で出世しても、鳥なき里の蝙蝠（こうもり）みたいで、なんだかむなしいな」
kotowaza-dictionary
彼は自分の部署では王様のように振舞っているそうだ。まるで鳥なき里の蝙蝠だよ。
rabdom tweets
人事面談で「鳥なき里の蝙蝠にならないように気をつけます」って言ったら（何言ってんだこいつ・・・？）みたいな空気になってしまいしょんぼりした。

僕らは所詮は井の中の蛙であり鳥なき里の蝙蝠。

These expressions are always tricky to handle - they are noun phrases but sometimes used in a proverbial way. But I think this should be glossed as an idion and a noun, as it was before Brian's edit.

GG5: 鳥なき里のこうもり. In the country of the blind, the one-eyed man is king. 【諺】 | A [Playing a] Triton 「of [among] minnows. 【諺】

I think the gloss in GG5, which we had previously, is quite appropriate. The bat/bird gloss is best flagged as literal.

@@ -26,3 +26,3 @@
-<pos>&n;</pos>
-<misc>&id;</misc>
-<gloss>a bat in a village without birds (who boasts of his skills in flying)</gloss>
+<misc>&proverb;</misc>
+<gloss>in the country of the blind, the one-eyed man is king</gloss>
+<gloss g_type="lit">a bat in a village without birds</gloss>

鳥なき里の蝙蝠	380	47.1%
鳥なき里のコウモリ	127	15.7%
鳥無き里の蝙蝠	126	15.6%
鳥なき里のこうもり	103	12.8%
鳥無き里のコウモリ	71	8.8%



Quite a good description here
https://dic.pixiv.net/a/鳥なき里の蝙蝠

https://proverb-encyclopedia.com/torinakisatonokoumori/
本当にその分野の優れた人がいないところでは、少し詳しいだけであたかもその分野の専門家のように威張り、偉そうにする人を意味する。
Boasting and acting more intelligent than you are seems to be critical to the meaning.

https://proverb-encyclopedia.com/torinakisatonokoumori/
"For want of a wise man a fool is set in the chair." (please don't use this, no one would know this idiom either)

Folk etymology (unconfirmable)
Chosokabe Motochika, who was active in the Sengoku period with the ambition of conquering Shikoku, was said by Nobunaga Oda to ridicule him for acting arrogant in Shikoku where there is no strong daimyo.

Some twitter insults:
On a politician's performance in Abe's wake
俺に言わせれば、大江健三郎なんてのは鳥なき里の蝙蝠だ。安倍公房が生きてたらノーベル賞なんて取れてなかったろうよ。

Twitterで見かける「開示請求」だの言葉遊びしたり、テクニック披露して学のないような層から崇められているような人、まさに「鳥無き里のコウモリ」😂

この鈴木マサと同じ、緑風会所属の自称保守系が多く、いずれも2015年と比較し2019年市議選で得票数を落としています。マサに「鳥無き里のコウモリ」の産物です。まともな候補者がいないのです。

On a thought-to-be-unqualified person giving medical commentary on corona（television commentator):
医師でもないのにマスコミに持ち上げられた「鳥無き里のコウモリ」みっともない。

Advice to Keio Students (just because you've been successful all your lives, don't be too proud...) 鳥無き里のコウモリである可能性をね。
慶應生、その中でも特に容姿にやんごとなき方々、就活期になると、
「え〜、私、僕、挫折なんて経験したこな〜い」（だって、私はお勉強できるし、顔も良いからモテてきたし、パパママにも怒られた事ないもん）って言う人まぁまぁいるが、
考えて欲しい。

鳥無き里のコウモリである可能性をね。

Had no idea what this meant from the glosses until I dug into it. (I thought maybe the bat was better at catching bugs with no birds around?).  

sankoku: 強いもの、優れたもののないところで、つまらないものが威張る。
This could literally be translated as an [expl] if the [lit] gloss remains unclear.  Of note つまらない and 威張る both have negative connotations. "idiots will boast/think highly of themselves".

It's a parable about not thinking too highly of your abilities.  You don't want to be the bat. To say that someone is a bat in a village without birds is to say that they act like they're smart, or they manage to appear successful to those around them, but they can only succeed in this because people with actual talent are not around.

”a man among the geese when the gander is away” is impressively obscure.  I thought maybe it was a mixed metaphor.  But no, a quote from ~1670 suggesting that a man is no good with women, except in an environment where no other men are around.  In that regard, its quality as an insult is similar.  But I suspect it has no application beyond womanizing, and since the idiom is not known, it's not of much use. 

"In the land of the blind" is often cited as analogous, but the nuance seems completely different.  鳥なき里の蝙蝠 is leveled as an insult to the bat for acting like he's talented, when in fact you'd find more talented birds if you left the village.  The "village" is not the universe( and though there were weak daimyo in Chosokabe Motochika's Shikoku, there were strong daimyo elsewhere in Japan).  In "the land of the blind", the one-eyed man never leaves that land.  That is the end-state, and his talent of sight is legitimately powerful. Being the one-eyed man is, if anything, an enviable position.

I also thought of the "big fish in a small pond" suggested (and discarded) some years back.  The problem there is that it also isn't really an insult.  It describes a situation in which someone gets a shock moving into more competitive waters. "He used to be a big fish in a small pond, but now he's struggling...."  Doesn't imply that the person is "full of them self" or possessing excessive hubris in their small pond.  It's just the reality of their situation.  They may be ignorant of the larger world, but this does not impugn their character.

There are related expressions in Japanese with various animal combinations.  Maybe the second most common (after this one) I could find is about weasels in place without a stronger breed of weasel... 鼬の無き間の貂誇り
自分よりも力の強いものやすぐれたものがいない所で威張ることのたとえ
https://proverb-encyclopedia.com/itatinonakimanotenhokori/

If there's no reasonably-equivalent, reasonably well-understood English idiom, I'd rather not try to force one in.

@@ -7,0 +8,3 @@
+<keb>鳥なき里のコウモリ</keb>
+</k_ele>
+<k_ele>
@@ -11,0 +15,4 @@
+<ke_inf>&sK;</ke_inf>
+</k_ele>
+<k_ele>
+<keb>鳥無き里のコウモリ</keb>
@@ -21,3 +28 @@
-<gloss>a man among the geese when the gander is away</gloss>
-<gloss>a one-eyed king in the land of the blind</gloss>
-<gloss g_type="lit">a bat in a village without birds</gloss>
+<gloss>a bat in a village without birds (who boasts of his skills in flying)</gloss>