The following I sent a few days ago to Ron Tozer, but with other readers posting some thoughts the text below may be of interest.
Alan Wormington, Leamington *********************************************** Ron, Some comments on your two main questions: (1) In my "Birds of Point Pelee" I am going to introduce a term I call "two-tier" migration, although I'm sure there is already a name for it somewhere in the literature. Anyways, this involves species that have, as the name implies, a two-tier migration strategy. Some examples during spring migration include American Pipit, Golden Plover, Pectoral Sandpiper, Baird's Sandpiper, Red-throated Loon and, of course, Red-necked Grebe. The shorebirds, for example, fly from South America to, for example, Texas, where they can be very common during March (some even north to Ontario at this season). But obviously these species do not then fly to their arctic nesting grounds, since these areas are frozen to late May (or even later). Therefore, they spend a considerable amount of time in arrested migration mode, fattening up and also changing into spring plumage, before finally barrelling north once more in late May. In fall migration, two examples of two-tier migrants include Dunlin and Bonaparte's Gull. With Dunlin, in the east the species migrates to (mostly) Hudson and James Bay in July in great abundance, but does not proceed further south until mid-September after they moult into winter plumage (but this initial event does result in the occasional individual being seen in southern Ontario as early as late June or early July, including Point Pelee). With Bonaparte's, adult birds invade the Great Lakes during August, but generally do not migrate again until December or even mid January (well AFTER they have completed a full moult from summer to winter plumage). NOTE: I make reference to this in my article on Bonaparte's Gull that appeared in *Point Pelee Natural History News*. With Red-necked Grebe, we have the same strategy. A similar pattern also occurs with Red-throated Loon. Birds arrive EARLY on the lower Great Lakes anytime from mid Feb through March in BASIC plumage. They then spend a long period of time in these areas before taking on another migration, with this second thrust putting them on the breeding grounds (late April through May). Between the two main flights, the birds attain breeding plumage and, presumably, take advantage of an increased food supply (and thus gain fat). Therefore, in your question as to the advantage of such a strategy, it is probably to take advantage of a good food resource before attaining breeding plumage and an eventual flight to the breeding grounds. The same strategy is also exhibited by Horned Grebe -- often you see the odd individual in "winter" plumage that has arrived during the period of mid Feb to late March, but it is late April to mid May when we see the majority of birds passing through (which by then are in breeing plumage). (2) Re this question, you ask why birds would migrate in such cold temperatures. Actually, they didn't! Here at Point Pelee there was a flurry of spring migrants (blackbirds, meadowlarks, geese, ducks, gulls, etc.) during the period of about February 15-20, because temperatures just south of here reportedly were briefly in the 60s F. I suspect that if you get some weather data from the East Coast around where Red-necked Grebe winters in large numbers, you will find that there actually were some warm periods when the birds started to appear in Ontario. Presumably this early migration occurs every year, but in most years the birds go mostly undetected since there is normally lots of open water for them when they get here. Well enough babbling . . . hopes this helps. Alan ________________________________________________________________ Sign Up for Juno Platinum Internet Access Today Only $9.95 per month! Visit www.juno.com Alan Wormington <[EMAIL PROTECTED]>
