What word in the passage means ‘seriously'?

Directions: Read the passage given below carefully and answer the question that follows.
Cattle Egret also known as 'Bagula' in Hindi, as it is very fond of walking along the cattle while they are grazing. It flies to its feeding grounds in the early morning and returns late in the evening. The beak is well adapted for feeding. It makes its nest in colony mostly in the tall trees. This Egret is different from the similar birds in being almost entirely an insect-eater, feeding on the insects and other pests which the latter disturb and also picking off ticks from the backs of cattle. The birds, of course, also eat frogs, worms and fish as well. They are extremely tame, allowing people to pass within a few feet without moving and then merely flapping sluggishly away or stalking solemnly off for a few yards before returning to feeding again. Although they are known for their interactions with humans but not all interactions between the two are beneficial. The Cattle Egret can be a safety hazard to aircraft due to its habit of feeding in large groups in the grassy verges of airports and it has been implicated in the spread of animal infections.