Annual Variation in the Cost of Polygyny: a ten year study of Great Reed Warblers Acrocephalus arundinaceus

Abstract

An isolated population of Swedish Great Reed Warblers was studied between 1984 and 1993 when almost every breeding adult and nestling were ringed. I examined between year variation in several variables that may affect fintness. In particular I looked at the reproductive success of females that can expect no or little male assistance (secondary females) in relation to females that are assisted by their males (monogamous and primary females). Return rates of females, the frequency of total losses and number of fledlings per female showed significant differences between years. The yearly mean number of fledglings per female was associated with the mean annual temperature during breeding. When an exceptionally warm year was excluded this was significant for both primary and secondary females. The success of secondary females relative to the success of primary females increased with increasing temperature implying that the cost of polygyny is higher in cold than in warm summers. The variation in clutch size and relative reproductive success of secondary and primary females increased over the ten year study period suggesting either that the study period was too short for capturing the variation of the variables or that these were subject to a systematic change over the study period. There were indications that the condition for breeding has deteriorated in the last years; clutch size decreased significantly over the study period and particularly low values of fledging mass and relative reproductive success were found in some of the most recent years. This might reflect that population density had reached a level when effects of intraspecific competition influences breeding results. Alternatively, five extremely mild winters may be responsible for a drastic increase of the lake's population of Crucian carps. Whether a large fish population could have caused a decline in invertebrate food for Great Reed Warblers in recent years is discussed.

<p class="NoSpacing1">THE EFFECTS OF WEATHER AND REED MANAGEMENT ON NESTING PARAMETERS OF THE GREAT REED WARBLER, ACROCEPHALUS ARUNDINACEUS (AVES: SYLVIIDAE)

“…Furthermore, nest predation was significantly lower in edges closer to grassland than at reed edges adjacent to water, suggesting that deeper water can be a limiting factor for some predators (Trnka et al 2009). As concerns the clutch size, Bensch (1995) found no significant relationship between clutch size and air temperature in long term variation. However, similarly to this study the hatching failure (as described by Bensch 1995), was not influenced by the air temperature.…”

“…Few Great Reed Warbler long-term studies analysed and discussed annual variations in polygyny (Bensch 1995), demographic variations and lifetime reproductive success (Hasselquist 1995), the effect of male arrival on their fitness (Hasselquist 1998), and how brood parasitism influences return rate in both sexes (Koleček et al 2015). However, we still know little about how weather circumstances and vegetation management affect breeding performance (e.g.…”

Female Settling Pattern and Polygynous Breeding in a Great Reed Warbler Population in Aomori Prefecture, Northern Japan

“…Recent experimental studies of male-removal (LYON et al 1987, WOLF et al 1988, BART & TORNES 1989 and long-term empirical studies (VIROLAINEN 1984, BENSCH 1995 have shown that the value of male assistance varies from year to year. This probably reflects year to year variation in parameters such as weather and food availability.…”

“…For example, in a Swedish population of Great Reed Warblers, a positive correlation was found between the mean temperature during a breeding season and the relative success of secondary status females to primary status females (BENSCH 1995).…”

Latitudinal, longitudinal and weather-related variation in breeding parameters of Great Reed Warblers in Europe: a meta-analysis

“…1). The study sites longitudinally ranged almost 2000 km, from Switzerland (Dyrcz 1981) to the Pskov region in Russia (Fedorov 2000), and latitudinally c. 2100 km, from Sweden (Bensch 1995) to Turkey (Uzun et al 2014). To explore the variation in these variables across Europe, we used the following parameters as potential explanatory variables: longitude, latitude, maximum temperature (mean temperature in July as the hottest month), daily mean precipitation in mm, the number of days with precipitation, and mean precipitation.…”