# Greatest Common Divisor vs Project FeederWatch

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.

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.

## The numbers

| Metric | Greatest Common Divisor | Project FeederWatch |
| --- | --- | --- |
| Price | $0.99 | **Free** |
| Rating | — | **[3.0 (68 ratings)](https://appshunter.io/ios/app/project-feederwatch/id1439222765/reviews)** |
| Number of ratings | — | **68** |
| Positive reviews | — | 33.3% of reviews |
| In-app purchases | No | No |
| Ads | No | No |
| Update frequency | Every 36 months | **Every 2 months** |
| Monetization | — | Ad-supported |
| Size | 1 MB | 63 MB |
| Requires iOS | **11.0** | 17.0 |
| Devices | iPhone, iPod | iPhone, iPad |
| Age rating | 4+ | 4+ |
| Developer | [Manfred Breede](https://appshunter.io/developer/414696754) | [Cornell University](https://appshunter.io/developer/382072985) |

## What reviewers say

### Greatest Common Divisor

[App page](https://appshunter.io/ios/app/greatest-common-divisor/id698020846)

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases:** none


### Project FeederWatch

[App page](https://appshunter.io/ios/app/project-feederwatch/id1439222765)

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.

**Highlights:** 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

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases:** none

**What reviewers like**

- 👍 Easy to use interface
- 👍 Straightforward tracking
- 👍 Neat data summaries
- 👍 Good support responsiveness
- 👍 Convenient app access

**What reviewers complain about**

- 💰 Unexpected payment required
- 🐛 Data loss and disappearing counts
- 🐛 App freezes and crashes
- 🐛 Login issues and errors
- 🐛 Inconsistent data saving

**Reported bugs**

- Birds saved then disappear
- Counts get lost
- Entries not saved consistently
- Part of data not recorded
- App deletes counts

**Requested features**

- Fix data loss issues
- Improve app stability
- Resolve login problems
- Add offline data entry
- Provide taxonomic sort option


## Frequently asked questions

### Is Greatest Common Divisor free?

Greatest Common Divisor costs $0.99, with no in-app purchases.

### Is Project FeederWatch free?

Project FeederWatch is free to download, with no in-app purchases.

### Do Greatest Common Divisor or Project FeederWatch have ads?

Neither Greatest Common Divisor nor Project FeederWatch shows ads.

### Which is updated more often, Greatest Common Divisor or Project FeederWatch?

Greatest Common Divisor ships an update every 36 months, and Project FeederWatch every 2 months. Most recently, Greatest Common Divisor was updated on September 27, 2026 and Project FeederWatch on October 29, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*