Is the article "a" omittable before "mortality rate"? How do you use a similar expression for "scattered splotches on the language map" in a different context? “In a normal event, the water would be cold, and the sun would come out and some of the turtles warm up,” Ms. Holmes-Douglas said. “You’re dealing with snow banks now that the turtles aren’t used to. They were exposed to more extreme temperatures. So we did expect a little bit more of a mortality rate. But, overall, I’m pleasantly surprised by the success.”