What observation led researchers to propose that chloroplasts evolved from cyanobacteria?

The theory that claims that, mitochondria and chloroplast's origin is bacterias, is called the endosymbiotic theory. It suggest that, plastids (one of them is chloroplast) and mitochondria were once, bacterias, and about 1.5 billions year ago they started to live with (inside) the pre-eukaryotic orgamisms. This is called endosymbiosis. The chloroplast originates from the cyanobacterias and the mitochondria from the proteobacterias. The some evidences that support this theory are these : -Mitochondria and chloroplast are formed with binary fission (the way bacterias reproduce) -When you remove a cell's mitochondria or it's chloroplast it can not produce them by itself. -Mitochondria and chloroplast have their own ribosomes (which produces protein) and they are smaller than the cell's own ribosomes, their ribosomes are similar to bacterias'.

Where are they though?

The return of the wolf to yellowstone national park will probably affect the bird population to some degree, not significantly. while wolves will hunt birds when necessary, they prefer to hunt larger prey. the bird population will most likely only be affected when hunting is scarce for the wolves. birds of prey will also probably not be affected as much as other birds who spend more time on the ground hunting for food as the tend to spend more time in the air or in trees since they do not need to stay on the ground for long due to the nature of the way they hunt.