Ewert et al. • DISTRIBUTION OF MIGRANT LANDBIRDS ALONG LAKE HURON 541 
TABLE 1. Mean importance values and densities of 
common trees at northern Lake Huron shoreline (shoreline 
and 0.4 km from shore) and inland (0.8. 1.6, and 3.2 km 
from shore) sites where point counts were conducted. 
Shoreline (n = 18) 
Inland > 
;n - 27) 
Species 
Importance 
value 
Density 
<trecs/ha) 
Importance 
value 
Density 
(tree s/ha) 
White cedar 
1.29 
381.8 
1.12 
344.5 
Balsam fir 
0.35 
97.3 
0.43 
97.1 
Quaking aspen 
0.29 
68.8 
0.39 
78.5 
Paper birch 
0.32 
68.7 
0.31 
68.5 
White spruce 
0.30 
77.0 
0.15 
29.4 
White pine 
0.13 
30.4 
0.14 
22.6 
Balsam poplar 
0.20 
98.1 
0.07 
12.8 
Red maple 
0.05 
12.1 
0.16 
28.1 
lo 10 times greater than the other common species 
(balsam fir, quaking aspen, and paper birch). 
Leaf emergence began on 6 May 1993 and 13 
May 1994 and leaves were fully expanded at all 
stations by 30 May 1993 and 1994. The phenology of 
paper birch and quaking aspen was highly correlated 
(r = 0.94, n = 1,052, P < 0.001), and offset by a 
constant of 0.25 (aspen leaf out slightly preceded 
birch leaf out); thus, we averaged phenology scores 
for the two species to estimate phenology as a 
function of distance from the shoreline. Average 
phenological development during spring was later 
nearshore than inland (F uo 75 = 29.10, P < 0.001; 
Rg. 4). Average phenology was not a function of 
distance from the lake in autumn (Fj,ioi 2 ~ 0.247, P 
~ 0.620). Most leaves remained on the trees 
throughout the autumn migration period. Little leaf 
^nescence (loss of chlorophyll) occurred during the 
fall sampling period. 
Midges .—Spring midge abundance was signif¬ 
icantly influenced by date (F 9t42 5 = 2.86. P = 
0.003). transect (F, li425 = 2.25. P = 0.012), and 
distance from shoreline (F 4 , 425 = 16.47, P < 
0.00J). More midges were counted at the 
immediate shoreline than at all other distances 
(Tukey p < 0.010). There were no differences in 
number of midges counted between any of the 
fther distances (Tukey P > 0.764; Fig. 5). Fall 
m idge abundance was influenced by date (F 9-425 
= 3.12, p = 0.001) and distance from the 
shoreline (F 4i425 = 8.49, P < 0.001). but not by 
transect (F, § 438 = 1.36. P = 0.189). There were 
more midges observed at the immediate shoreline 
inland (Tukey P < 0.015; Fig. 5). There 
w ere no differences in estimated midge abun¬ 
dance between any other distances. 
Julian Day 
FIG. 4. Average (± SE) aspen and birch phenology 
score by day along the northern Lake Huron shoreline. 
Inland encompasses all sampling points not at the 
immediate shoreline. Julian Day 130 = 10 May; Julian 
Day 150 = 30 May. 
FIG. 5. Mean (± SE) midge abundance as a function of 
season and distance from the northern Lake Huron 
shoreline, 1993-1994. 
