immature eagles in Africa tend to be much darker and more heavily marked both above and below than martial eagles. Predatory physiology Martial eagles have been noted as remarkable for their extremely keen eyesight (3.0–3.6 times human acuity), partly due to their eye being nearly as large as a human's eye. Due to this power, they can spot potential prey from a great distance, having been known to be able to spot prey from as far as away. Their visual acuity may rival some eagles from the genus Aquila and some of the larger falcons as the greatest of all diurnal raptors. The talons of martial eagles are impressive and can approach the size, especially in mature females, of those of the crowned eagle despite their slenderer metatarsus and toes compared to the crowned species. Accipitrids usually kill their prey with an elongated, sharp hind toe claw, which is referred to as the hallux claw and is reliably the largest talon in members of the accipitrid family. The average length of the hallux claw in unsexed martial eagles from Tsavo East National Park, Kenya was found to be . In comparison, the average hallux claw of a large sample of golden eagles was similar at . Meanwhile, the three largest clawed modern eagles were found to measure as such: in small samples, the Philippine eagle and crowned eagle had an average hallux claw length of and , respectively, and harpy eagles have an average hallux claw length of approximately . A further sample of martial eagles averaged in 6 males and in 7 females, with the median between the sexes being , these being the largest talons of all booted eagles behind only the crowned eagle. The inner claw on the front of the foot of the martial eagle is especially sizeable proportional to other extremities and unusually can approach, if not reach, the same size as the hallux claw. This inner claw was found to average , in comparison to that of the crowned eagle which measures . The tarsus is quite long in martial eagles, the fourth longest of any living eagle and the longest of any booted eagle species, seemingly an adaptation to prey capture in long grass, including potentially dangerous prey. The bill is of medium size relative to that of other large eagles, with a mean culmen length from Tsavo East of . The bill