Any subjective or objective analysis of recent extralimital bird occurrences in NJ reveals that several SE, US species are appearing more in NJ and in other NE, coastal states. Most of these species have static or declining US populations so the records are not a reflection of simple range expansions driven by healthy outbreeding.
In recent years we have seen an increase in the NE of White-faced Ibis, White Ibis, Roseate Spoonbill, Anhinga, Magnificent Frigatebird, Black-bellied Whistling Duck, Sandwich Tern, Wilson‘s Plover, American Avocet, Ground Dove, White-winged Dove, Cave Swallows, Mississippi Kite, Swallow-tailed Kite and most recently (Nov 2010) the second NJ record for White-tailed Kite. Numerous breeding species are also expanding their ranges N but not S (see 4/07 issue Conservation Biology, http://news.mongabay.com/2008/0116-birds.html ). Additionally we are seeing reports of SE insects and fishes reaching further N than in past decades.
Are the higher taxa simply feeding on the lower taxa that are, for some reason, further N? Indeed the kites feed on Odonates (dragonflies)some of which are migratory. Many invertebrate, and vertebrate species including birds have a protracted fall migration tuned closely with temperatures which influences food availability. Perhaps dragonflies, other insects and fishes are lingering further N in summer and fall and this is attracting some of these S bird species N. Its seems that multiple species of animals are further N than they were just a few decades ago inferring a broad, large scale event is occurring.
Lets imagine a scientifically trained Rip Van Winkle arrived on the modern scene. We will shield our guest from biased, special interest messages from both sides of the Climate Change issue (and J. Hartmann and L. O'Boyle, associates of mine). We will give him NO temperature data or advise him that atmospheric CO2 levels have increased from 270 ppm to near 390 ppm in the geologic blink of 250 years. We will let him study only the zoogeographic distribution of animals over the millennium----compared to what we are witnessing recently. What will he report is causing these range expansions and records that are showing a rapid, northerly movement of animals in our area?