As noted in prior posts, an effective method for assessing the occurrence of global warming is to examine the multitude of micro-effect studies. While these do not usually indicate rates of change, they help to provide substantial credence to the actuality of climate change.
A study of the changes in wolf prey selection may be an indication of an effect of climate change. When wolves were first introduced into Yellowstone National Park in 1995 after a 23-year absence, the main component of their diet during the early winter in the northern range was elk calves. As winter wore down the elk (e.g., less food, impact of cold), adult males became easier prey; bulls made up about 1/3 of wolves' diet by the end of winter.
From 2004 to 2008, when the weather was warmer and drier, the elk had less vegetation to eat, and the males were less "bulked up" for the winter. Because the bulls were weaker (both from the mating season and the lower intake of food), the wolves selected them for prey earlier in the winter. As a result, the wolves made fewer kills than in previous years, but each elk taken provided a larger meal.
The study was presented at the June meeting of the American Society of Mammologist, and unfortunately has not been published. However, some interesting work on the same subject matter by the same researchers can be found at http://www.esajournals.org/doi/abs/10.1890/04-0953?journalCode=ecol, http://www.esajournals.org/doi/abs/10.1890/06-1254.1?journalCode=ecap, and http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B8JDB-4TXDRVR-N&_user=10&_coverDate=12%2F31%2F2008&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1410732027&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=edb653b026646b6dd5b1e65365217685.
An interesting site on wolf behavior in hunting Bison in the Yellowstone area can be found at http://www.carnivoraforum.com/index.cgi?action=display&board=canine&thread=928&page=6.