1 pound ≈ 0.453592 kilograms
Given that 18 bee hummingbirds weigh 1 pound, we can calculate the number of hummingbirds that weigh 1 kilogram:
Number of hummingbirds for 1 kilogram = (1 kilogram / 0.453592 kilograms/pound) * 18 hummingbirds/pound
Number of hummingbirds ≈ 39.68 hummingbirds
Therefore, approximately 39 to 40 bee hummingbirds together would weigh one kilogram.