Date: Sun, 5 May 2002 10:02:46 -0400 Reply-To: Maryland Birds & Birding Sender: Maryland Birds & Birding From: "rick@blazie.net" Subject: Re: Summer Tanager "invasion" MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit "Shireen Gonzaga" wrote: > A birder recently told me that there was a study > that indicated that the northward range of some > migrant species were getting even more northward > compared to historical records. He suggested that > this was an effect of global warning. > 1) does anyone know about this study and where > it was published? > 2) what's been the historical range of Summer > Tanagers in MD, and has there been an increase > of nesters in the past decade or so? Second things first: Summer Tanagers have not expanded in Maryland as far as we know. There appears to have been a slight population decline and reduction in range over the past fifty years. First things second: There have been quite a number of articles about global warming and the effect on bird populations. Most are speculative and try to predict future changes (try the American Bird Conservancy website). A few try to establish that global warming has already changed some patterns, especially migration. It is a good idea to be extremely skeptical of those papers. Most are obviously flawed and a few qualify as junk science. Range changes, if they come as a result of global warming, will be very slow. That is because birds change their ranges not primarily in response to temperature but to habitat and it takes at least decades (centuries or millenia is more like it) for the habitat to change in response to small increases in temperature. Some "southern" birds, such as Blue Grosbeak, have expanded north in recent decades but that is attributed to habbitat change unrelated to global warming, in this case the alteration of woods into weedy/seedy waste areas. At the same time many "northern" birds have moved south, such as Golden-crowned Kinglet. Global warming is the current hot-button environmental topic. It appears to be real and ought to scare the bejabbers out of us but that does not mean that there is yet any evidence of it in changing ranges and populations of birds. There may (emphasize may) be some very slight shift north in a few species of European butterflies that may (emphasize may twice) be partly in response to global warming but it appears that those species are dependent on primarily perennial flowers that could expand northward relatively (empasize relatively) quickly. A couple of papers purporting to show that North American migrant landbirds are arriving earlier as a result of global warming are so full of holes that it is impossible to conclude anything from them except that the authors were eager to get on the bandwagon early. It is possible, for example, to take the same data source, use the same statistical method, and "prove" that bird migration is actually getting later. Global warming, if it continues as the models predict, will eventually change bird distribution but the change will be glacial and no one currently on the MDOsprey listserv will live long enough to see it. In the meantime a lot of birds are shifting their ranges both north and south in response to human alteration of the landscape and those changes will make it harder to determine which, if any, are the result of glocal climate change. The overlooked (it is not as sexy) effect of glocal warming on birds has been hinted at by a study in Europe that shows that at least one species is initiating nesting earlier as temperatures increase. The reason is that insect hatches are occurring slightly earlier. The results are somewhat prelimianry but if true (and it makes biological sense) it could have a profound effect over time. The reason is that a gene for earlier migration is likely to spread very slowly in the population while the insect hatches get earlier much faster. That means that birds will be arriving after the period when the maximum number of prey are available and food shortages can cause increased nest failure. That could lead to a fairly rapid population decline for many birds whose migration is timed for arrival at the moment when nesting is most likely to be successful. Little work is being done in this area yet. Sorry for the length of this but it is a complicated subject and there is a lot of twaddle being written about it at the moment. Global warming appears to be a real threat but bad science is bad science even when it is intended to support a good goal. Rick Eirik A.T. Blom 4318 Cowan Place Belcamp, Md 21017 410-575-6086 rick@blazie.net ======================================================================= > To leave the MDOsprey list, send e-mail to > listserv@home.ease.lsoft.com with the following message in line 1: > signoff mdosprey > ====================================================================== > = ======================================================================= To leave the MDOsprey list, send e-mail to listserv@home.ease.lsoft.com with the following message in line 1: signoff mdosprey ======================================================================= =========================================================================