COMPENSATORY NEWBORN FAWN MORTALITY

Northern white-tailed deer populations have historically demonstrated patterns of boom and bust, increasing during a series of mild winters only to crash following a tough one. Most recently, this roller coaster population pattern has been characterized by lower highs as well as lower lows, resulting in steadily declining deer numbers.

Although reasons for this decline vary regionally, and a variety of factors are involved, the primary reason for fewer deer is annual deer recruitment rates fail to keep pace with deer mortality rates. On an annual basis, this simply means that not enough newborn fawns survive to replace deer that die.

Researchers have identified a multitude of factors that might cause excessive newborn fawn mortality, however, predation (by coyotes, black bears, bobcats and wolves) is commonly singled out as the primary cause.

Granted, some studies in the South have demonstrated significant increases in newborn survival rates following coyote eradication. However, I’m not aware of any such documentation in the North. In fact, research conducted in Delaware, where there were no effective natural deer predators, recently reported 55 percent newborn fawn mortality due to natural causes other than predation.

At least on Northern deer range, I argue that excessive newborn fawn mortality credited to predation is more often “compensatory” in nature. That is, the combination of tough winters and poor quality deer wintering habitat are more important, because resultant nutritional stress sets the stage for birth of under-sized weak fawns, a breakdown in maternal care traits and exaggerated estimates of fawn loss due to predation.

In other words, it’s my contention that a high percentage of fawns born to food-stressed does die shortly after birth anyway — predators merely take advantage of an