31 Figure 5 continued.

Transcription

1 Figure 5 continued. 31

2 32 ponding correlations between annual indices and mean annual lake levels for each species considered. Interestingly, trends for some species at inland routes were more positively correlated with lake level changes than were they at coastal routes (e.g. Piedbilled Grebe, Sora), and the trend for American Bittern was moderately positively correlated (r = 0.57, P = 0.24) lake level changes (this species occurred at too few coastal routes to provide a reliable trend estimate for the coastal category)(table 2). Black Tern, Coot/Moorhen, and Virginia Rail trends at coastal routes were more positively correlated with lake level changes than at inland routes, similar to that for basin-wide comparisons. Lake Erie Trends for Black Tern, Least Bittern, Marsh Wren, Coot/Moorhen, Pied-billed Grebe and Sora at coastal marshes tracked well with, and were quite positively correlated with mean annual water level changes of Lake Erie (Table 3, Figure 6). For several species, trends at inland routes were not available because of their low route-level occurrences, and for those species where trends were available, most correlated poorly with Lake Erie water level changes. However, Virginia Rail (r = 0.44, P = 0.38) tracked Lake Erie s water levels moderately well, albeit not significantly (Table 3, Figure 6). Common Yellowthroat s trend was moderately negatively correlated with Lake Erie water level changes. Lake Ontario Absolute changes in Lake Ontario s water levels were comparatively less than were they for any other lake basin considered. Further, although Lake Ontario s water levels peaked during the same year as did all other Great Lakes (i.e. 1997), a marked flux in water levels occurred between 1998 and Because coastal route-level occurrences were too low for many species, coastal route trends were calculated for only four of the nine marsh bird species examined for lake level comparisons (Table 4). Among those species where sample sizes were sufficient to estimate coastal route trends, Marsh Wren correlated positively well (r = 0.84, P <0.05), Virginia Rail moderately correlated positively (r = 0.54, P = 0.27), and Coot/Moorhen correlated poorly (r = 0.28,

3 33 Table 3. Proportion of routes where species were present, proportion of route-years where species were present, and correlations between annual population indices and mean annual water levels of Lake Erie for select marsh bird species surveyed by MMP volunteers between Coastal Inland Species % Rts Present 1 % Rte-yrs Present 2 r a % Rts Present 1 % Rte-yrs Present 2 r a American Bittern N/A N/A Black Tern N/A Common Yellowthroat Least Bittern N/A Marsh Wren Coot/Moorhen Pied-billed Grebe N/A Sora Virginia Rail a - Pearson's correlation coefficient between population indices and mean annual water levels of Lake Erie from Common denominator for all species is 30 for coastal routes and 53 for inland routes 2 - Common denominator for all species is 116 for coastal route-years and 196 for inland route-years

4 34 Figure 6. Annual indices of select marshbird species at coastal and inland MMP routes throughout the Lake Erie basin as compared to mean annual water levels of Lake Erie

5 Figure 6 continued. 35

6 36 Table 4. Proportion of routes where species were present, proportion of route-years where species were present, and correlations between annual population indices and mean annual water levels of Lake Ontario for select marsh bird species surveyed by MMP volunteers between Coastal Inland Species % Rts Present 1 % Rte-yrs Present 2 r a % Rts Present 1 % Rte-yrs Present 2 r a American Bittern N/A Black Tern N/A Common Yellowthroat Least Bittern N/A Marsh Wren Coot/Moorhen Pied-billed Grebe N/A Sora N/A Virginia Rail a - Pearson's correlation coefficient between population indices and mean annual water levels of Lake Ontario from Common denominator for all species is 26 for coastal routes and 28 for inland routes 2 - Common denominator for all species is 103 for coastal route-years and 104 for inland route-years

7 37 Figure 7. Annual indices of select marshbird species at coastal and inland MMP routes throughout the Lake Ontario basin as compared to mean annual water levels of Lake Ontario

8 Figure 7 continued. 38