Scientists at San Francisco State University, in collaboration with researchers from PRBO Conservation Science, have discovered that birds in central California are bulking up. Not only are they gaining weight, but their wingspans have also increased over the last few decades. The suspect in this alteration is climate change.
According to Bergmann's Rule, animals at higher latitudes tend to be larger. This may be due to their ability to store fat for protection in cold weather. Therefore, some scientists predicted that global warming would actually cause animals to get smaller. Because severe weather is more common with the changing global climate, the birds may be getting larger to help store fat during unpredictable weather conditions. Changes in climate may also bring about alterations in food availability which could impact the body composition of birds. As mentioned in a prior post, this trend of increasing body mass in birds has been seen before. Fossils of penguins originating from warmer climates (ex: Eocene) show that the animals were indeed larger than modern penguins.
Birds are not the only vertebrate that is growing with the changing climate. In a prior post, the same observations were made of marmots. However, the reason for the weight gain was attributed to earlier arousal from hibernation giving the animals more time to pack on the pounds before the next winter set in.
Clarke et al., Paleogene equatorial penguins challenge the proposed relationship between biogeography, diversity, and Cenozoic climate change. PNAS. 104(28): 11545-11550, 2007.
RE Goodman, G Lebuhn, NE Seavy, T Gardali, JD Bluso-Demers. Avian body size changes and climate change: warming or increasing variability? Global Change Biology. In Press.