Info

Species arranged according to habitat preference, shallow (ephemeral) to deep (permanent) waters. Only studies with both sex and age groups represented are shown.

From Johnson & Grier (1988) in which the original references may be found. For other waterfowl studies, see Rohwer & Anderson (1988).

Species arranged according to habitat preference, shallow (ephemeral) to deep (permanent) waters. Only studies with both sex and age groups represented are shown.

From Johnson & Grier (1988) in which the original references may be found. For other waterfowl studies, see Rohwer & Anderson (1988).

other nesting areas. Species that show low site-fidelity also show low mate-fidelity, because pairing occurs annually on or near nesting areas and former partners do not normally move together to the same places. In the American Avocet Recurvirostra americana, individuals were found to move up to 325 km between breeding sites in different years (Robinson & Oring 1997). Many other waterside birds, which require specific conditions for nesting, change their breeding places between years, in association with changes in water levels and vegetation, or the flooding and exposure of sandbanks.

In conclusion, high site-fidelity and short dispersal distances are characteristic of bird populations whose habitats or food supplies stay reasonably stable in distribution from year to year, whereas low site-fidelity and long-distance dispersal are shown by populations whose habitats or food supplies vary in distribution from year to year. The adaptive value of moving when conditions deteriorate is obvious, because this is likely to improve individual survival and breeding success in the conditions prevailing. Because of the moves, numbers in particular localities fluctuate greatly from year to year, in line with changes in habitat or food conditions, and some localities which support high densities of breeding birds in one year may be wholly devoid of birds the next. Differences in dispersal patterns between species have led some authors to divide birds into two types: those with limited natal dispersal, and even more limited breeding dispersal (strong site-fidelity), and those with wide-ranging natal and breeding dispersal (little or no site-fidelity). In practice, however, variation between these extremes is continuous, and the same species may lie at different points on the continuum in different parts of its range, depending on the stability of local habitats and food supplies (Chapters 18 and 19).

Was this article helpful?

0 0

Post a comment