Greatest Common Divisor vs Project FeederWatch
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
Greatest Common Divisor
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This app calculates the largest divisor that is common to two positive integers.
Project FeederWatch
Easily report bird sightings from your feeder for scientific research. Track your statistics, access past counts, and learn about local feeder birds. Contribute to a large database that aids conservation efforts.
- Report winter bird sightings
- Track sighting statistics
- Access past count archives
- Contribute to bird population database
- Discover best food and feeder types
- Identify and learn about feeder birds
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Do you feed birds? You can report what you see for science. Project FeederWatch, a joint project of the Cornell Lab of Ornithology and Birds Canada, monitors winter feeder-bird populations in North America. The FeederWatch Mobile App is a new way for Project FeederWatch members to contribute their bird counts. Sign in to: •Report birds that visit your count site in winter (US and Canada only) •Track your sighting statistics in real time •Access your archive of past counts from all years •Contribute to North America’s largest database on feeder birds •Find out what food and feeder types work best for the birds overwintering near you •Identify and learn about feeder birds FeederWatch Mobile automatically syncs with the web version for seamless multi-platform support. Your data become immediately available for scientific research, education, and conservation. Thank you for helping birds!
Screenshots
Verdict
The clearest difference is price: Project FeederWatch at Free against Greatest Common Divisor's $0.99. Project FeederWatch also leads on update cadence (every 2 months vs every 36 months). Greatest Common Divisor's advantage is iOS requirement (11.0 vs 17.0). On ads, in-app purchases and device support there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Project FeederWatch is free to download; Greatest Common Divisor costs $0.99 up front. Neither carries in-app purchases, so what you see is what you pay.
Greatest Common Divisor ships an update every 36 months, Project FeederWatch every 2 months. The most recent releases landed on September 27, 2026 and October 29, 2026 respectively.
| Parameter | Greatest Common Divisor | Project FeederWatch |
|---|---|---|
| Price | $0.99 | Free — better |
| Rating | — | 3.0 (68 ratings) — better |
| Positive reviews | — | 33.3% of reviews |
| Number of ratings | — | 68 — better |
| Update frequency | Every 36 months | Every 2 months — better |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | — | Ad-supported |
| Devices | iPhone, iPod | iPhone, iPad |
| Requires iOS | 11.0 — better | 17.0 |
| Further details — not scored | ||
| Size | 1 MB | 63 MB |
| Age rating | 4+ | 4+ |
| Developer | Manfred Breede | Cornell University |
Bugs and requests
Greatest Common Divisor
Not enough reviews yet to summarise bugs or requests.
Project FeederWatch
Reported bugs
40 issues- Birds saved then disappear
- Counts get lost
- Entries not saved consistently
- Part of data not recorded
- App deletes counts
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- App freezes/hangs regularly
- Connection fails repeatedly
- App is slow to respond
- Opens to a blank black screen
- App doesn't recognize submitted through browser
- Entering total observation doesn't work
- Freezes after entering most data
- Frequent freezes and server problems
- App freezes when coming up
- App freezes frequently on iPad Pro
- Forced to close and reload app
- No way to enter data offline
- App freezes after using for 2 minutes
- Login problem fixed but causes freezing
- Login fails, incorrect password/account not activated
- Cannot alter/fix incorrect bird count
- Cannot delete sightings
- Cannot zero out a bird count
- Account not activated message
- Latest update doesn't work
- Server doesn't want to connect
- App doesn't connect
- Screen goes all black
- Logins become a nightmare for months
- App goes to a totally black screen after appearing to be launching
- Lost bird count due to black screen lock up
- Regularly fails to recognize login
- Zero observations reported initially
- Cannot log in, account not activated
- App doesn't work at all after update
- App directs to log in on website, but still doesn't load data
- Can't enter dates correctly
- App doesn't report a problem with version, but newer version exists
- Repeatedly freezes to the point of needing to power off/on
- Froze if left open too long
Requested features
19 requests- Fix data loss issues
- Improve app stability
- Resolve login problems
- Add offline data entry
- Provide taxonomic sort option
Show 14 moreShow fewer
- Enable data entry by alpha code
- Fix blank black screen on launch
- Allow alteration/deletion of incorrect counts
- Add French language version
- Improve iPad functionality
- Make app more robust for all users
- Ensure consistent data saving
- Fix server connection issues
- Update app more frequently
- Improve user interface for better screen utilization
- Fix issues with switching between apps
- Allow editing of submitted counts
- Improve handling of large counts
- Ensure all species counts are saved
In-app purchases
Greatest Common Divisor
No in-app purchases
Project FeederWatch
No in-app purchases
Questions
Is Greatest Common Divisor free?
Is Project FeederWatch free?
Do Greatest Common Divisor or Project FeederWatch have ads?
Which is updated more often, Greatest Common Divisor or Project FeederWatch?
Other comparisons
