Flight call rates of migrating thrushes: effects of wind conditions, humidity and time of day at an illuminated offshore platform

Abstract

Many bird species call during migration, but call rates not necessarily reflect migration intensity. They rather seem to increase under deteriorating flight conditions. Often, nocturnal mass collisions at illuminated structures coincide with such conditions and are accompanied with high call rates of migrants. Thus, call rates could act as an indicator for situations with high collision risk for birds namely at offshore sites with hardly any alternatives for landing. In the face of increasing numbers of offshore wind farms knowledge about the environmental conditions in which maximum call rates occur, is needed for mitigation measures. In this first long‐term study at an offshore site in the southern North Sea we investigated the effect of weather on the frequency of flight calls of three thrush‐species at an illuminated platform. Flight calls were registered automatically during three autumn migration seasons. Besides generally higher call rates from 5 to 2 h before until 6 h after midnight, call rates increased with tailwinds, a change of the tailwind component during the first part of the night, offshore crosswinds and very high humidity. A monitoring programme is suggested that could help to reduce mass mortalities at illuminated structures.

Factors influencing Manx Shearwater grounding on the west coast of Scotland

“…() did not detect any evidence for visibility influencing the fallout of Atlantic Puffin Fratercula arctica . This can be explained by the fact that more birds start their migration with clear sky conditions (Hüppop & Hilgerloh ). Our study confirmed both these trends presented in research by Phillips and Lee () and Hüppop and Hilgerloh (), with slight increases in predicted grounding when the visibility was either low or high.…”

Applying bioacoustic methods for long-term monitoring of a nocturnal wetland bird

“…However it was difficult to estimate the absolute number of animals because the call rate differs between species and even within a species, the call rate being strongly dependent on the particular environmental conditions (Farnsworth, 2005;Farnsworth et al, 2004;Hüppop and Hilgerloh, 2012). Buxton and Jones (2012) found that nocturnal call activity can at least provide information on the relative population density of cave breeding birds.…”

Temporal and spatial variation of a winter soundscape in south-central Alaska

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