Hello
Okapis: depends on what part of April. The weather is very changeable in New York in April and some days may be too cold. The later it is in the month, the more likely the okapi will be out.
Congo Gorilla Forest
For transportation, see my earlier post with the link to the Bronx Zoo site.
To go from New Haven or to New Haven will require going through Manhattan (downtown New York City) if using trains. So if you are visiting New Haven now, you can take the MetroNorth train into New York (Grand Central Station) and then either switch to subways to go to the zoo directly by train from Grand Central Station: take the Harlem Line to Fordham and either walk to the zoo entrance or take the Bx9 bus eastward to 183rd Street and Southern Blvd. The walk is not far... especially by Beijing standards

Anyone can direct you from the train station in the Bronx to the zoo. The Botanical Garden is across the street from the train station (and lies between the train station and the zoo) and the guard at the Garden gate can also direct you if need be
Wednesdays are reduced entry fee days and the zoo can be very crowded if the weather is nice
Hours & Rates