The average cost for migration days is 130 kJ, of which 71.3 kJ is spent on flight alone; the remaining 24 days are stopovers where an average of 88 kJ d-1 is expended, assuming an ambient temperature similar to that in central Illinois.
from: http://www.nature.com/nature/journal/v423/n6941/full/423704a.html
The article says elsewhere the average body weight per bird is 30g, so let’s convert to kg and divide:
71.3 kJ expended flying per day / 0.003kg = 23,767 kj/kg expended per flying day
On a flying day, they fly for about 265km, so let’s convert again:
23,767 kj/kg / 265 km = 90 kj/kg/km
This article estimates that running at speeds up to 22km/hr uses about 1 kcal/kg/km, so let’s convert our flying number to kcal:
90 kilojoules = 21.5105163 kilocalories (says google)
So our birds are using about 22kcal per kg to fly each kilometer, and a person uses roughly 1kcal per kg to run a kilometer.