Does a 1lb crow expend only 7.68 Watts to fly at 37 km/h?
The number cited by Orville looks quite reasonable. The crow is just cruising along, not banking, accelerating or climbing.

Now add a climb speed of just 1 meter (3.3 feet) per second, and the additional power is 5,93 W. Let it circle with 60° bank angle, which would double the required lift, and the power for staying aloft increases to 15.36 W.

Next comes the flight speed, which goes up with the root of the wing loading. The American crow has a wing chord between 25 and 33 cm and a wing span between 85 and 100 cm. Taking the average puts their wing area at maybe 0.25 m² (it is almost rectangular, after all), and their wing loading at 1.8 kg/m². I would expect that a battery-powered model would have a higher wing loading, maybe 5 kg/m². The required power goes up with the third power of speed, and the speed itself increases with the square root of the wing loading. This makes the model of the crow fly at 62 km/h and consume a power of 35.5 W - just for straight and level flight. Add some margin for acceleration, banking flight and climbing, and the 50W/lb rule looks quite reasonable.