8.0 Waterfowl Distribution and Abundance on Long Point Bay

8.2 Historical changes in waterfowl distribution and abundance

8.2.2 Overall Spring And Fall Waterfowl Days At Long Point, 1974-1997

Migration trends since the 1970s have been similar in spring and fall, with high numbers in the 1970s, substantial declines in the 1980s, followed by increases during the 1990s (Figure 8.18). Low numbers during the 1980s were probably not caused by any deficiency or habitat change at Long Point, since we know that several species that migrate through Long Point experienced low continent-wide numbers at that time (Dilworth-Christie and Dickson 1997). Waterfowl numbers at Long Point have been steadily increasing since 1991 (Figure 8.18). This can probably be attributed to at least one of two factors: 1) the

substantial increase in the continental populations of most waterfowl species during this time (Dilworth-Christie and Dickson 1997) has simply resulted in more birds migrating through Long Point; and/or 2) the ready availability of zebra mussels since the early 1990s may have resulted in either more birds using Long Point, or birds staging for longer periods (Petrie and Knapton 1999).

Long Point receives considerably more waterfowl use in the fall than it does in the spring. Low waterfowl numbers during the fall of 1995 and 1996 (especially divers) are surprising, given the high continental populations of most species during that time. Waterfowl generally migrate more quickly in the spring than in fall as they must arrive on breeding areas in time to lay eggs, raise young, and replace flight-feathers prior to the fall flight. In contrast, fall migration is much more protracted; there is no specific time-frame for birds to arrive on the wintering grounds. Generally the only constraint is that birds stay ahead of bad weather and freeze-up. Therefore, it may not be that fewer birds migrate through Long Point in the spring; they may simply be staying for a shorter period of time. Annual waterfowl use of Long Point is much more variable during spring than fall, and this has been attributed to the fact that during early springs, much larger numbers of birds stop at Long Point and tend to stay for a prolonged period of time.