The MOS is a statewide organization of local chapters. Each sets its own dues, a portion of which goes to the state Society. At-large membership (no local chapter affiliation) is also available. The MOS membership year begins September 1.
The benefits received from Maryland Ornithological Society membership dues are not considered to be substantial, as determined by criteria in IRS Publication 526. Therefore, members can claim a tax deductible charitable contribution for the full amount of their membership dues.

MOS doesn’t release its membership list to any other organization and uses it only for communication with members.