"A question that remains open is risk to birds that migrate at night at very low altitudes. Virtually no studies have been conducted, in any area, of night migration at altitudes below 200-250 feet. Hence, the potential for risk to nocturnal migrants flying at these altitudes is not known. Most previous studies using radar and ceilometer strongly suggest that only a small percentage of nocturnal migrants fly below 250 feet above ground, but those techniques usually have limited abilities to detect low-flying birds and to discriminate birds at different altitudes. Until technology allows researchers to quantify the low-altitude migration, risk cannot be assessed."

—Paul Kerlinger, avian consultant for industrial windpower, 2002, 2000.