For some reason this post caused me to search to see if there are types of birdseed which are not suitable for ducks. From a few minutes of reading, I’m relatively sure now that at least all common types of birdseed are fine for them. But, along the way, I found this LLM slop https://plantnative.org/can-ducks-eat-bird-seed.htm (URL rendered unclickable since it is spam) which strongly implies that ducks are not in fact birds:

• “Yes, ducks do eat bird seed. Although bird seeds are specifically prepared to meet the nutrient demand of birds. But still, bird seed can be served as a snack to ducks in limited amounts.”
• “Bird seeds are loaded with nutrients and can be beneficial for ducks the way they are for birds.”