Territory quality and reproductive success: Can water pipits Anthus spinoletta assess the relationship reliably?

Variation in avian reproductive success is often caused by differences among territories in food supply, safety from predators and microclimatic conditions at the nest. Yet, in some habitats these components of territory quality, and hence future reproductive success, are difficult to assess at the time of settlement. Here, we analyse territory quality for Water Pipits breeding in an unpredictable alpine habitat and relate it to settlement patterns and reproductive success. In the study area, prey biomass differed between various vegetation types and steadily increased during the breeding season. Territory-specific prey biomass was negatively correlated to snow cover during the pre-breeding period. Males, on average, arrived prior to females, and both sexes settled earlier in prey-rich than in prey-poor areas. Early settling malemale also occupied larger territories, early settling females showed a longer time lag between settlement and clutch initiation than late ones. However, prey biomass, territory size and time lag as well as male and female age were not related to clutch size and number of fledglings per brood and season. The only factor significantly determining reproductive success was the occurrence of nest predation for which we could not find an environmental predictor. Apparently, the birds could not either, because both sexes settled independent of later predation. In the discussion we address the question why Water Pipits cannot reliably assess habitat quality when choosing a territory and what alternatives they have.

Bollman K., Reyer H.U. & Brodmann P.A., ARDEA 85 (1): 83-98.