Citizen science participation spans biodiversity recording, wildlife surveys, astronomy, environmental monitoring, and data classification. Reported totals range from millions of platform users and observations to focused local projects with hundreds of observers. The figures below retain each program’s measurement period and describe reported participation or output rather than a single globally representative survey.
Table of contents
- The scale of major citizen-science platforms
- How observations and identifications accumulate
- City Nature Challenge participation and biodiversity
- Long-running wildlife survey participation
- NASA GLOBE and environmental observations
- Eclipse and heliophysics volunteer projects
- Citizen science in global biodiversity data
The scale of major citizen-science platforms
Two large platforms illustrate different forms of participation. iNaturalist combines field observations with community identification, while Zooniverse records repeated volunteer classifications across research projects.
According to iNaturalist, more than 6 million people use the platform each month. Its current platform summary, accessed in 2026, reports more than 300 million verifiable observations and more than 4 million community members worldwide. The same source says iNaturalist observations represent about 25% of all described species on Earth. About 7,000 peer-reviewed papers cite iNaturalist data.
Zooniverse reported a different kind of milestone in “One BILLION Classifications!”. In June 2026, volunteers reached 1 billion classifications. More than 3 million volunteers had participated in Zooniverse projects since Galaxy Zoo launched, covering the period from 2007 through June 2026. Those volunteers participated from 160 countries.
| Program and period | Participation or output reported | What is being counted |
|---|---|---|
| iNaturalist, current figure accessed 2026 | More than 6 million monthly users | Platform use |
| iNaturalist, current figure accessed 2026 | More than 300 million observations | Verifiable observations |
| Zooniverse, 2007–June 2026 | More than 3 million volunteers | Project participants |
| Zooniverse, June 2026 | 1 billion classifications | Volunteer classifications |
These totals are not directly interchangeable. A monthly user, a community member, a volunteer, an observation, and a classification represent different units of participation. They nevertheless show the range of ways that public contributions can be organized into research data.
How observations and identifications accumulate
iNaturalist’s milestone history shows how participation can accelerate over time. In a June 17, 2025 update, iNaturalist marked 250 million verifiable observations. That milestone represented nearly 4 million observers worldwide, while more than 400,000 people had identified observations submitted by other users.
The same iNaturalist update gives three sequential accumulation periods. The platform took 14 years to reach its first 100 million verifiable observations, covering 2008 to 2022. It reached its second 100 million in the following two years, from 2022 to 2024. The next 50 million arrived in a little under one year, during 2024–2025.
The records also moved beyond the platform itself. More than 100 million iNaturalist records had been shared with the Global Biodiversity Information Facility by June 2025. iNaturalist data had contributed to more than 6,500 scientific publications by that date.
The sequence is useful for understanding participation without treating it as a fixed annual rate. The first 100 million, the second 100 million, and the next 50 million were measured over different periods. The reported figures show increasingly rapid accumulation in the cited milestones, but they do not establish a forecast for future totals.
City Nature Challenge participation and biodiversity
The 2024 City Nature Challenge connected short observation windows with local and global biodiversity records. In the 2024 results, the global event ran from April 26–29, 2024 and produced 2,436,000 observations. It documented more than 65,600 species, included more than 3,940 rare, endangered, or threatened species, involved 83,500 participants, and covered 690 cities.
Local projects show how the global total can be distributed across communities. The 2024 Chicagoland City Nature Challenge produced 11,100 observations and recorded 1,670 species. A 2024 western Massachusetts project recorded 4,128 observations and 1,015 species, with 297 observers.
| 2024 City Nature Challenge location | Observations | Species | Participants or observers |
|---|---|---|---|
| Global challenge | 2,436,000 | More than 65,600 | 83,500 participants |
| Chicagoland | 11,100 | 1,670 | Not stated in the cited result |
| Western Massachusetts | 4,128 | 1,015 | 297 observers |
The global event also recorded more than 3,940 rare, endangered, or threatened species. That measure identifies the conservation significance of some records, while the total observation count measures the volume of contributions. Neither number should be read as a complete inventory of biodiversity in the participating cities.
Long-running wildlife survey participation
Annual wildlife surveys can produce both large participation totals and long historical series. The RSPB Big Garden Birdwatch reported that almost 600,000 people took part in January 2025. Participants counted more than 9 million birds and recorded more than 80 bird species.
The survey’s longer record extends back to 1979. From 1979 through 2025, more than 200 million birds had been counted. RSPB estimates that participants spent more than 12.6 million hours watching and counting garden birds over that period. These are cumulative program estimates, not a standardized measurement of each participant’s time.
The January 2025 results included 3,201 Redwings and 2,885 Fieldfares. The RSPB explanation of why every count matters reports that House Sparrow counts were down 64% from 1979 to 2025. The comparison spans the beginning of the survey record and 2025; it is not a claim about a single year’s change.
This combination of annual participation and historical comparison gives the survey two uses. The latest count describes activity in January 2025, while the 1979–2025 series provides a longer context for changes in recorded bird numbers. The figures remain tied to the survey’s methods and participating locations.
NASA GLOBE and environmental observations
NASA’s GLOBE program illustrates participation organized through schools, educators, students, and scientific communities. NASA reported that the program connected scientists, teachers, and students in 126 countries in 2021. By then, GLOBE participants had gathered and shared more than 200 million Earth-science observations since the program began.
For the 2024 eclipse campaign, NASA described GLOBE participant communities in 127 countries. The NASA eclipse citizen-science report also noted that more than 30 million people lived along the path of the April 8, 2024 total solar eclipse.
The campaign included repeated local measurements. In the weeks before April 8, 2024, Alpena Elementary students collected eclipse-related temperature and cloud readings 10 times per day. At an El Paso, Texas observation site, solar coverage reached about 80% at maximum. These examples describe specific sites and activities rather than the complete campaign output.
The country totals and observation totals use different measurement periods: 126 countries and more than 200 million observations were reported for 2021, while 127 countries describes the 2024 campaign communities. Keeping those periods separate matters when comparing the program’s reach over time.
Eclipse and heliophysics volunteer projects
NASA’s Growing Heliophysics Citizen Science Strategically report summarizes a portfolio for 2023–2024. More than 36,000 volunteers participated in eclipse citizen science during the heliophysics big year. The portfolio also reported 52 million ham-radio contacts.
Several projects measured participation through devices, teams, training, or uploaded data. SunSketcher received data uploads from 32,000 phones. The Distributed Electronic Network project reported 80 teams, while Citizen CATE involved 35 teams. Eclipse Soundscapes reached more than 900 people through training programs.
The Eclipse MegaMovie effort had more than 100 gold-star participants upload 1,097 GB of data. The portfolio reported 379 applications and more than 225 participants for another heliophysics citizen-science activity. In its leadership measures, women accounted for 50% of team leads and state coordinators and 75% of regional coordinators.
These values represent different forms of contribution during 2023–2024. A phone upload, a training participant, a team, an application, and a ham-radio contact are separate units. The report’s figures therefore describe the breadth of the portfolio rather than one combined volunteer headcount.
Citizen science in global biodiversity data
Citizen observations also enter shared biodiversity infrastructure. A GBIF report on eBird said the eBird Observational Dataset exceeded 275 million occurrences after its 2015 update. eBird volunteers added almost 64 million records in 2015, and the dataset grew 30.1% from 2014 to 2015.
The same report, published in December 2016 about the 2015 data, said the update pushed open-access species-occurrence records available through GBIF past 700 million. The date is important: these are historical totals associated with the 2015 update, not current 2026 counts.
A separate GBIF citizen-science analysis described the contribution in 2018. Citizen-science observations made up around 50% of biodiversity occurrence records on GBIF in the analyzed period. Six of GBIF’s top 10 datasets were classified as citizen-science datasets. Birds accounted for 617 of the top 800 species ranked by citizen-science occurrence count, and the leading seagull species had more than 8 million citizen-science occurrence records.
The 2018 percentages and rankings are historical and descriptive. They show how strongly citizen-generated observations featured in the analyzed GBIF records, but they should not be interpreted as current 2026 shares or rankings. Together with the iNaturalist, eBird, survey, and NASA figures, they demonstrate several measurable outputs of participation: observations, classifications, species records, environmental readings, uploaded data, and scientific publications.