Meaning of "catch birds for"?

I am reading B. Traven's adventure The Treasure of the Sierra Madre, which is about three men who secretly go prospecting for gold. On their way home with their new-found loot they cover their tracks by tearing down their mining camp. Howard (the most experienced of the party) verbally beams with pride over a job well done. Dobbs, another member, takes offense at Howard's response. The quoted section can be found here:

The mine was leveled to the satisfaction of Howard. Anybody now coming upon the mine by chance would never think that a mine had been worked here, or if at all, not during the last hundred years.

"Doesn't it give you guys a real joy to look at the place now?" Howard asked with pride in his voice.

"All right," Dobbs said, "you have it your way and you feel happy, so please, for the love of Mike's booze, leave us in peace with your feelings. Sometimes I think you must have been a preacher, only the hell of it is I can't figure out what church it was you wanted to catch birds for."

When I found a definition of bird (Definition 5.a) that is slang for fellow, I took Dobbs' words to catch birds for to be reminiscent of the Christian saying fisher of men, meaning the minister is actively looking for people to convert. In past conversations, Dobbs has been known to use slang like mug to refer to people. But being more familiar with the usages meaning a young woman or a person, especially one who is odd or remarkable, I thought this usage unlikely and continued to look for another.

So I wondered if Dobbs was making an allusion to bird dogs, who retrieve birds for their masters. (One might say a minister retrieves the lost for a higher power, a superior in the church or for God.) This could be an insult to Howard, the slight being that Howard would be a subordinate instead of the senior/equal he was when mining with Dobbs. This insult makes sense in this context, because Dobbs has a history of viewing Howard as a taskmaster, as shown by Dobbs's outburst when he cuts his own hand at the beginning of the chapter. But this analogy of bird dogs seems tenuous and elaborate.

I've searched Google for "catching birds," but the most relevant results are the proverb "A bird in the hand is worth two in the bush." I wondered if Dobbs was speaking of some duty, tradition, or superstition associated with ministers, but I have found nothing.

What does "to catch birds for" mean?

I imagine it's an echo of this expression (as defined by OED)...

(strictly) for the birds
trivial, worthless; appealing only to gullible people. orig. and chiefly U.S. colloq.

Dobbs clearly isn't interested in anything Howard has to say. He's implying that despite Howard's "evangelical" enthusiasm, nobody else would be interested either, except gullible people as above.

OP is on the right track with bird = fellow - but here it's specifically birdbrained (stupid) fellows. The word catch is also used figuratively here (Dobbs means interest, draw in, captivate, impress).

It could be that in the US Catholic priests used to capture doves before celebrating Easter, and then released them at the end of the Holy Mass to symbolise the ascension of the Holy Spirit.

In Italy there are several festivals that celebrate Easter by releasing doves in the air. I was wondering if they did the same in the US.

La Madonna Che Scappa in Piazza - Abruzzo Region

Sulmona, in the Abruzzo region, celebrates Easter Sunday with "La Madonna Che Scappa in Piazza"

"On Easter Sunday people dress in green and white, colors of peace, hope, and resurrection, and gather in the main piazza. The woman playing the Virgin Mary is dressed in black. As she moves to the fountain, doves are released and the woman is suddenly dressed in green.

I found this Youtube clip filmed at Santa Jose, 2013, entitled: "The releasing of the holy ghost doves today." Skip to the 3.40 mark to see the dove being freed. The video is very dull and amateurish but it proves (to me) that even today, in some parts of the US, this tradition still carries on.

EDIT:

I think you must have been a preacher, only the hell of it is I can't figure out what church it was you wanted to catch birds for.

Dobbs insults Howard by calling him a preacher this leads me to speculate that Dobbs was not "born" in the Catholic faith, (priests are not normally referred to as preachers) however, by mentioning birds and asking who Howard caught them for, it is possible that either he was familiar with the Easter festival tradition of releasing live doves in the air or maybe he was attempting to cover up his background by ridiculing his (plausible) religious upbringing.

Not having read the book I can only make suppositions, but the dots do connect.