One of the most vulnerable age classes are neonatal animals and juveniles, or the year's young. While surviving to second or third year doesn't guarantee you'll survive to old age, if you're a deer, it does mean you're fairly less likely to die. Adults are very good at surviving, since evolution has shaped them to be surviving machines, capable of hyper-vigilance, amazing running speeds, and so on. The young, however, enjoy much less of that sort of protection. There tends to be lower survival for the young of the year, and this can be a major factor governing population fate - if you die young, it's hard to do much breeding.
Re-colonizing wolves provide a wonderful mini-experiment to see what the effects of their presence or absence is on various age groups. Kim Berger and Mary Conner, both at Utah State University at the time, studied the effects of re-colonization on pronghorn neonatal survival. Berger and Conner selected two study sites with wolves, and one that was free of wolves in Wyoming. Coyotes were much less abundant at the sites with wolves than they were at the sites with wolves, as they had demonstrated in a previous study.
Fawns were located through a good old fashion leg-work (they must have good vehicle access out there!), and through watching gravid females until they dropped their fawns. They would capture the neonates, weigh them, age them, record the sex, and assess over-all health in a few categories before fitting them with a breakaway radio collar with a mortality sensor. When the animal dies, the radio signal from the collar changes, allowing the researches to swoop in and look for cause of death. Some things they would look for include
- whether the fawn was alive at the time of the attack
- tracks, scat, hair, and any caches that might help them identify the predator
- signs of starvation or other accidents.
This fits nicely into a framework that I've previously mentioned, which is the "Meso-predator release hypothesis." The idea is that wolves or other apex predators (bears, cougars, etc.) keep middling scavenger-predators (such as fox, coyote, racoon, skunk) suppressed when they're around and healthy. They can suppress them through feeding on common prey, attacking meso-predators directly, and so on. This is a top-down effect, where high trophic levels (animals that do bulk of the eating other things) influence the composition of the lower trophic levels (prey; the things that are eaten).
Within the state of Alaska, it begs the question whether there are significant numbers of meso-predators, and whether they are similarly released in times of intensive management. A entirely separate and important question is whether this release negatively impacts prey populations. To my knowledge, no one has done any sort of extensive study of meso-predators in the state. Our knowledge of background fox and coyote density is not very good, and after asking several people, I begin to suspect there are no density estimates for regions of the state. Given that, I am sure no one has looked at meso-predator densities during periods of IM. Anyone who knows otherwise is encouraged to email me! However, the latter most question is probably best identified - there have been studies of calf mortality after bouts of IM, and I don't anyone's identified a shift in mortality towards meso-predation.
Berger KM, & Conner MM (2008). Recolonizing wolves and mesopredator suppression of coyotes: impacts on pronghorn population dynamics. Ecological applications : a publication of the Ecological Society of America, 18 (3), 599-612 PMID: 18488620