An American news article titled "N.J. aquarium welcomes 4 baby penguins, and yes they're insanely cute (PHOTOS)" starts like this:
Eggs have been a-crackin' at Camden's Adventure Aquarium, welcoming four tiny African penguins to the crowd-favorite exhibit, Penguin Island.
The new penguins were hatched in two separate clutches -- the first on Dec. 10 and 14, the second on Dec. 23 and 26.
Adventure Aquarium Curator of Birds and Animals Michele Pagel said the baby birds are very vocal, growing strong, and have great appetites.
Does the context mean that the baby birds are becoming strong?
If not, shouldn't it be "strongly" instead of "strong"?
Alternatively, couldn't it have been "strongly" instead of "strong"? If the writer had intended it to mean that the baby birds are growing quickly (not becoming strong), could he have said, "The baby birds are growing strongly"?