Falconiforms in immature plumage are generally observed to be:

Immature falconiforms, or birds of prey, often exhibit larger body sizes compared to their adult counterparts at the same stage in their development. This phenomenon can be attributed to several factors related to their growth and development. During the immature stage, these birds are in a rapid phase of growth as they prepare for the rigors of adult life, including hunting and territory establishment.

In many species, juveniles may have longer wingspans or greater mass due to the energy demands of their developing muscles and the need to be fully prepared for survival. Their larger size can also help them compete for food more effectively, which is crucial before they reach maturity.

The option suggesting that they are smaller than adults does not account for the growth spurt that typically occurs in young birds of prey. Therefore, stating that immature plumage birds are larger than adults reflects a better understanding of avian developmental biology, specifically in raptors. The other choices do not accurately represent common attributes of falconiforms in their immature stage.