My comments (I have no data) regarding the topic of declines brought up by SeEtta and commented on by Adam would be:
Things are definitely moving north. CBC's are certainly not very scientific, particularly the numbers from one count in one year, but the shear numbers of them conducted over many accumulating decades makes them increasingly valuable as a dataset when analyzed as a whole or perhaps regionally. Analyzing bird population trends is very complex. Another way of putting it is oversimplification is dangerous. Seeing the forest for the trees is a statistical nightmare. While warming or climate change might be one "forest" or big picture factor, drought in a particular year, rodent populations, weather up north (or down south) and other "trees" might be more important influences on what we see on a given count day or course of a single year. Robins certainly like our modification of the environment in the way of installing woody plants with berries, which is probably much more influential than temperature (similar to mockingbirds and multiflora rose plantings, cardinals, etc. back East) However, the two things, climate and plantings, are not inseparable because climate certainly influences the survival and vitality of plants. I would say the trend in wood ducks is highly influenced by the proliferation of Russian-olives in wetlands over the same time period of the analysis and could well be the main reason we have seen increases, particularly in winter. Magpies are probably as much influenced by recent West Nile Virus exposure as climate. Rough-legged Hawks seem to fluctuate with rodent numbers, which are driven by summer rains the previous summer that produce plants with seeds to feed rodents. Physically, I don't think wood ducks and robins are particularly prone to cold snaps, but the influence of temperature on their food might be an issue. Just some thoughts. It is all very interesting and should provide our birding some purpose far beyond mere lists. Dave Leatherman Fort Collins --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/cobirds?hl=en -~----------~----~----~----~------~----~------~--~---
