 However, the researchers found a 50\% reduction in the female Great Tits' total sleep duration during this period in densely populated urban centers.
<fluency>  However, the researchers found a 50\% reduction in the female Great Tits' total sleep duration during this period in densely populated urban centers.
 However, the researchers found a 50-percent reduction in the female Great Tits' total sleep duration during this period in densely populated urban centers.