When the subject of the main clause and the subject of the adverb clause are the same person or thing, the adverb clause can be reduced (shortened). Reduced adverb clauses do not contain a main verb or a subject. They consist of a marker and a participle (either a present or a past participle) or a marker and an adjective.
Examples:
When linguists are studying a minority language, they don't neglect its social functions, (full adverb clause).
When studying a minority language, linguists don't neglect its social functions, (reduced clause with present participle).
Although it had been limited, the regional language was still operational, (full adverb clause).
Although limited, the regional language was still operational, (reduced clause with a past participle).
Although he was nervous, the lecturer gave a wonderful speech, (full adverb clause) Although nervous, the lecturer gave a wonderful speech, (reduced clause with an adjective).
You will most often see reduced adverb clauses with the markers although, while, if, when, before, after, and until. Reduced adverb clauses are NEVER used after because.