Out of curiosity...

Informal survey
I conducted an informal study of participants at a restoration work party. The work party was advertised primarily by email and word-of-mouth by leaders of a University of Washington Restoration Ecology Network (UW-REN) capstone project group. It took place Sunday, February 12 from noon until 3pm at Yesler Creek, not far from the UW Seattle campus. After their work, volunteers were invited (not obligated) to complete a half-page paper survey. All 8 participants completed the survey, and the results are displayed on the homemade charts below.

Findings
All 8 participants reported that they were motivated to volunteer to "Have fun", and indeed each of them reported that in fact they "Had fun". Each of them also reported the benefits of "Spending time with friends" and "Connecting with nature". These benefits correlate well to the initial motivations of the majority of participants, which were "To spend time with friends", "Spend time outdoors", "Give back to the earth", and "Feel like I contributed something important", in addition to having fun. The majority of participants reported receiving these desired benefits, and most of them also enjoyed "Getting exercise", "Feeling relaxed and satisfied", "Getting to know local environment", and "Participating in local community".