Dave,
Could probably break this down into three categories -(1) no breeding ever on site (2) unsuccessful breeding the previous year and (3) successful breeding the previous year - and see if there is any substantial variation between them (albeit we may be working with fairly small sample sizes for each category). If I send you that stats can you do the analysis?
......I also think that the previous years successful breeding facilitates an early return, especially with non passerines. We have noted this with LRP, Avocet and Common tern which are easy to record. .......
Thanks to Phil for the data, I have now tested your theories, John.
For
Common Tern, there is a significant correlation between arrival date at UW and breeding success in the previous year (
i.e. number of fledged young):
r (28) = -0.509,
p < 0.01 (figure 1).
For
Little Ringed Plover, there is
no significant correlation between arrival date at UW and breeding success in the previous year (
i.e. number of fledged young):
r (26) = -0.195,
p = 0.32 (figure 2).
However, for
LRP there is a significant correlation between arrival date at UW and the total number of breeding pairs:
r (26) = -0.521,
p < 0.01 (figure 3).
For
LRP, one-way analysis of variance (ANOVA) with post-hoc HSD test gives the following result:
F (2, 30) = 16.47,
p < 0.01
Successful breeding versus unsuccessful breeding (in previous year): No significant difference in arrival date
Successful breeding versus no breeding (in previous year): Significant difference in arrival date (
p<0.01)
Unsuccessful breeding versus no breeding(in previous year): Significant difference in arrival date (
p<0.01)
A possible interpretation of these results is as follows:
Ringing studies show that Common Terns have a high level of natal philopatry (young birds return to their place of birth) as well as adult breeding site-fidelity. Therefore, the higher the number of birds fledged at UW the more return in subsequent years and the higher the likelihood of earlier return. Common Terns typically breed for the first time in their 3rd year.
Little Ringed Plovers, however, have been shown to have low levels of natal philopatry, even though adult site-fidelity is high. Therefore, this may explain why their early arrival only seems to depend on the total size of the adult breeding population and not on breeding success in previous years. LRP's typically breed for the first time in their 2nd year.
:t: