His mentor was George Lowery (a prominent ornithologist in his own right) under whom Howell studied birds for his PhD, which he graduated with in 1951.

[1] His dissertation was on the "Natural history and geographic variation of the Yellow-bellied Sapsucker", which would be published in The Condor.

[2] The dissertation examined how gene flow is kept very low between subspecies as a result of differential migration, habitat, and color based dimorphism.

His most important contributions were in studying thermoregulation in birds, which he frequently accomplished in the hot deserts of North Africa.

The Auk cites his study on Egyptian plovers as the most important of those works, discovering that the birds carry water in their feathers to transfer to the sand around their buried eggs to keep them cool in the desert heat.