Endocrine influences on parental care during a short breeding season: testosterone and male parental care in Lapland longspurs (Calcarius lapponicus)

In males of socially monogamous birds, plasma testosterone (T) typically declines to low levels during the parental phase. Studies on multiple-brooded species indicate that high T may be incompatible with high-quality paternal care. The length of the breeding season may affect the costs and benefits of high T and its effect on paternal care. We studied the effect of experimentally elevated T on paternal care in a single-brooded species with a short breeding season, the Lapland longspur (Calcarius lapponicus). We monitored T levels and parental behavior in 16 males with subcutaneous T implants, 14 males with empty implants, and 14 unimplanted males. We videotaped nests when nestlings were 2–3 days old and again at 4–5 days. T males with 2- to 3-day-old young visited nests and fed young less often than control males, and the mates of the T males compensated with elevated visits and feedings. However, when nestlings were 4–5 days old, T males visited their nests at normal rates – though feeding movements remained below normal – and T females visited and fed at normal rates. Nestling mass and nest success were similar in both groups. Overall, high T suppresses paternal care in Lapland longspur males. The partial improvement of paternal care when nestlings are older, despite high T, may be related to the short 6-week breeding season of this arctic species, and the consequently reduced benefits of sexual behavior late in the breeding season. Received: 2 February 1998 / Accepted after revision: 2 November 1998     

Determinants of male mating success in the red bishop (Euplectes orix)

We studied sexual selection in the red bishop, Euplectes orix, a colonial, polygynous weaverbird widely distributed over sub-Saharan Africa. Male reproductive success measured in terms of the number of nests accepted by females and the number of eggs and nestlings in all the nests on a male's territory varied considerably. The standardized variance (variance/mean²) in male reproductive success ranged from 0.505 to 1.737 in different years, indicating a high potential for sexual selection in this species. An analysis of genetic parentage for 432 nestlings by non-radioactive, multilocus DNA fingerprinting confirmed that male reproductive success (number of young sired on the territory) in this species can be reliably estimated by the measures introduced above. In all 4 study years there was a strong positive correlation between male mating success and the total number of nests that males built in their territories. The number of nests built can be partitioned into the number of weeks a male held a territory and his nest-building performance. Both factors exert a significant positive effect on male mating success and in combination explained between 53.3 and 86.3% of the variation in male reproductive success. Male morphological characters were found to be of no importance. Males that established a territory in the following season built more nests and held their territories for longer than males that did not establish a territory in the following season, suggesting that these measures might be indicators of male condition and quality. Male nest-building performance (number of nests built per week) seems to be unrelated to male condition or quality. Received: 8 January 1999 / Received in revised form: 7 June 1999 / Accepted: 13 June 1999     

Song rate as a signal for nest site quality in blackcaps (Sylvia atricapilla)

In this study we examine male song output as a measure of nest site quality in blackcaps (Sylvia atricapilla). Song rate, breeding success, predation on nests and reaction to playbacks were investigated in individual males. Habitat features determining nest site and song post quality in terms of vegetation cover were compared between successful nests and nests that had suffered predation. We then related song rate of unmated males to habitat factors in territories and nesting sites in order to examine a possible predictor function of blackcap song for habitat quality. Several habitat features are responsible for variation in nesting success. These features also correlate with song rate of unmated males. The study indicates a potential role of song rate in the advertisement of territory quality. Furthermore, the data suggest that females use song rates rather than territory quality in mating decisions. The information females may gain about male quality in relation to territory quality are also discussed.     

The influence of potential reproductive rate and variation in mate quality on male and female choosiness in the sand goby, Pomatoschistus minutus

Recent models of choosiness in mate choice have identified two particularly important factors: the potential reproductive rate (PRR) of the choosing sex relative to that of the chosen sex, and the variation in quality of potential mates. This experimental study tested how these factors affected choosiness in male and female sand gobies, Pomatoschistus minutus. We manipulated relative PRR by means of water temperature, and mate quality by means of body length. The choosing male or female was offered a choice between two mates with either a small or a large difference in body length representing a small or a large variation in mate quality. Choosiness was measured as (1) preference for the larger mate, and (2) as whether or not spawning occurred with the smaller mate, while the larger mate was visible but screened off. We found that females preferred large males, and that their level of choosiness was affected by variation in male quality, but not by their own relative PRR. Males, on the other hand, seemed unselective in all treatments and were in general more likely than females to spawn with their provided partner. This suggests that in the sand goby, variation in male mate quality has a greater influence than relative PRR on facultative changes in female choosiness. However, a general difference in PRR between males and females may be one important factor explaining the observed sex difference in choosiness. Received: 17 April 2000 / Revised: 24 June 2000 / Accepted: 17 July 2000     

The Extended Kalman Filter (EKF) as a tool for the assimilation of high frequency water quality data

The Extended Kalman Filter (EKF) was applied to the analysis of high frequency field measurements of dissolved oxygen (DO), water temperature, salinity, collected by multiparametric sensors in the lagoon of Venice. This paper focuses on the practical aspects of the implementation of the EKF as a data assimilation technique and does not deal with the problems associated with the identification of the model. In this regard, the EKF has proved to be a useful tool for the updating of the estimates of the parameters of a simple DO-chlorophyll model, which can be used for linking the high frequency data to meteorological forcings, such as solar radiation and wind, and to other low frequency measurements of water quality parameters, such as the concentrations of Chlorophyll a and nutrients. The model can subsequently be used as a tool for checking the consistency of all this data, and may also be employed for controlling the quality of the data collected by the multiparametric sensors.