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Fawn Mortality in the Big Woods

Recently I re-watched a webinar on YouTube called “Who’s Eating Bambi?” which was based on a three-year collaborative effort between the Pennsylvania Game Commission (PGC) and the Pennsylvania Cooperative Fish and Wildlife Unit at Penn State University (PSU). The study was designed to determine fawn survival rates in the Keystone State, particularly in sections that are considered big woods.

According to Duane Diefenbach, leader of the co-op unit which consists of the PGC, U.S. Geological Survey, and PSU, about half of Pennsylvania’s fawns are born by the end of May. The balance are born by the end of June and early July.

Begun in 2015, the research focused on two study areas, one in the Susquehannock State Forest in northcentral PA and the other in the Rothrock and Bald Eagle state forests in the central part of the state. Both areas contained similar habitat and were in close proximity to the locations of the PGC’s last fawn study in 2000-2001.

Although fawn studies began back in the 1960s, Diefenbach says they weren’t really effective until the 1990s, with the improvement of tracking equipment. Pennsylvania has been on the cutting edge of tracking technology and helped design the collars that are now commonly used during such studies. Also, of the agencies that have studied fawn survival, the PGC is the only one to do so twice while using two different study areas each time. This has provided a larger data set from which to draw comparisons and provide a more complete picture of fawn survival rates.

Tess Gingery, a graduate student from PSU, worked on the recent study and noted two major differences that have occurred since the first one took pace. First, predator densities have increased by 40% over the past 18 years. And second, whitetail densities decreased by 21% between 2002 and 2005 but have remained stable (or slightly increased in some WMUs) since then.

The three major predators of fawns are black bears, bobcats, and coyotes. Of course, predation isn’t the only way fawns die. Humans play a role as fawns encounter fences, roads, agricultural processes, and hunting harvest. There are natural factors (not counting predation) at play, too, such as starvation, abandonment, and disease.

The highest number of mortalities occur during the first eight weeks of a fawn’s life. Most of this is due to predation. Humans were the main cause of death for fawns 25 to 30 weeks of age, which corresponds with hunting season.

It’s interesting to note that fawn survival was similar in both study areas. Through hunting season, fawn survival to 34 weeks of age was .40 in the northern zone compared to .51 in the southern zone. The northern zone is 98% forested while the southern zone has more agricultural areas.

Here’s a more detailed breakdown of the numbers:

In the northern zone, 82 fawns were captured and there were 44 mortalities. Causes of death were humans (6 – 1 roadkill and 5 hunter harvests), natural (5), and predation (33).

In the southern zone, 83 fawns were captured and there were 38 mortalities. Causes of death were humans (5 – 2 roadkills and 3 hunter harvests), natural (13), predation (18), and unknown (2).

In the northern zone, the number one predator of fawns is black bears, which claimed 18 fawns, followed by coyotes (8), bobcats (2), and unknown (5). In the southern zone it was a different story. Coyotes were the number one predator with 6 fawn kills followed by black bears (5), bobcats (5), and unknown (2).

Equally interesting are the similarities, and differences, between the current study and the one done in 2000-2001.

In the Quehanna Wild Area in 2000-2001, predation was still the number one source of fawn mortality with 69.5% (up to 75% now in the northern zone). However, natural causes ranked second at 18.6% (only 11.4% now) and humans were third at 10.2% (13.6% now).

In 2000-2001 in Penns Valley, humans were the number one source of fawn mortality with 42.6% (only 13.2% in the southern zone now), natural causes were second with 38.3% (34.2% now), and predation was third at 17% (47.4% now).

Regardless of the actual causes of mortality, Gingery notes, fawn survival rates have remained stable over the past 20 years, and that’s a good thing.

During the webinar, Asia Murphy, also a PSU graduate student, discussed how distribution of predators in forested habitat affected fawn survival rates. Data collected from trail camera surveys showed that black bears and whitetail deer prefer to use forested habitat. However, when it comes to rearing fawns, whitetails prefer non-forested habitat.

For instance, does generally spend 80% of their time in forested habitat, which is roughly the same amount of time black bears spend in the forest. Come fawning season, though, does begin using non-forested habitat 90% of the time, whereas black bears still tend to stick to the forested habitat 80% of the time. Mama Doe is clever indeed!

This data could very well explain why fawn survival rates tend to be higher in agricultural areas. The habitat is more favorable for deer and less favorable for predators. In fact, the co-op unit at PSU has documented in other studies the propensity for does to migrate from forested to non-forested land to birth their fawns, and once those fawns are physically able to escape predators, they return with them to their original range.

According to PGC Deer and Elk Section Leader Dr. Christopher Rosenberry, predator impacts on deer are a part of deer management. “Each year, we monitor fawn to doe ratios in the harvest,” he said in the webinar. “When these data are collected in the firearms season, most predator mortalities have already occurred.”

If predators begin taking more fawns, fawn to doe ratios in the harvest will decline. This provides a good indicator about predator populations, too, although managing predators isn’t easy.

As Rosenberry noted, black bears are a major predator, but hunters do not want bear populations reduced to increase deer. Also, hunters want lower coyote populations, and despite no closed season, coyotes continue to thrive here.

“These two examples show the social and biological changes associated with attempting to control predators for the benefit of deer populations,” said Rosenberry. “Fortunately, there is one wildlife management action that can be effective should predator impacts become too high, and that is adjustment of anterless deer hunting opportunities.”

In short, even in areas with lots of predators, decreasing the number of anterless permits will still allow the deer population to grow. Currently, though, despite an abundance of predators, no changes are in sight as fawn survival rates have remained steady the past 20 years and deer populations remain stable or increasing in every WMU across Pennsylvania.

It should be noted that this year’s gun season will return to the concurrent buck and doe format. It will be interesting to see if these increased opportunities have any impact on populations moving forward. If you want to view the webinar referenced in this article, here is the link: Who’s Eating Bambi?


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