It could also be word-of-mouth... You know, one person has a good, positive experience with the rescue (friendly people, reasonable prices, honesty as to the bird's medical condition and/or disposition, a process that is neither too onerous nor too lengthy on the applicant, etc] and they will recommend it to somebody else. I used to recommend a rescue but I stopped doing it because, apparently, they have changed their methods lately. I knew the people from before they had the rescue and kept in touch with them after they started it - even taking several 'difficult' birds from them. I had been there a few times and thought they were doing their best by the birds (even though I did not agree on the diet they were given or the lighting but I did not hold it against them because I know I am a maniac when it comes to these things
] but I found out they lied about a bird's medical condition and that the new person in charge of adoptions was not willing to make her decisions on a case-by-case basis and rejected an applicant for a stupid reason so I no longer recommend them.