Some bird species have eyes that weigh more than their brains.

Although there are differences among species, in general, a bird's eye
weighs more than its brain. For example, the combined weight of an owl's
eyes is around a quarter of an ounce (7 g), or about 4% of its total body
weight. Human eyes comprise well under 0.1% of our body weight. The average
bird's eyes take up approximately 15% of its head, while human eyes
comprise just 1% of the whole head. Because of the keen vision necessary
for spotting food sources from high in the air, birds' eyes are of vital
importance for their survival. In fact, birds' eyes take up a greater
proportion of their total body mass than the eyes of any other vertebrate.