Actually there is more to that story. There's better food than bread but many who once counted on humans for their diet are now starving to death. https://www.google.com/amp/s/www.cbc.ca/amp/1.5329117
"A bird eating bread" is a noun phrase where "eating" describes the bird's current action, independently of the main verb of the sentence. This description would use the "contemporary adverbial participle" form "jedząc." By contrast, in "ptak je chłeb," eating is the main action of the sentence, not just a description of the bird.
Because it can be :) For 99% of the Polish verbs, there is no difference between English Present Simple and Present Continuous.
This 1% are Verbs of Motion, and so-called 'habitual verbs'. Actually, there is a habitual verb "jadać" (Ptak jada chleb) which would render Present Simple here, but "Ptak je chleb" is also perfectly fine for "A bird eats bread".