Experimental manipulation of the dawn and dusk chorus in the blackbird Turdus merula

Abstract

We present experimental and correlational data that demonstrate that both the nutritional state of the male and his mate's fertility affect the timing and intensity of dawn and dusk song in the blackbird (Turdus merula). Food supplementation leads to paired males singing earlier, for longer, and at higher peak rate at both dusk and dawn succeeding the treatment. We argue that the timing, not just the intensity, of song conveys information about the male's phenotypic condition. Both dawn and dusk song start earlier and have longer duration as a male's mate reaches peak fertility indicating that, in agreement with literature on the great tit (Parus major), song at this time has particular significance in mate guarding for paired males of monogamous species. We discuss the relative importance of these factors as functional explanations for the dawn chorus.

Mate guarding in the Seychelles warbler is energetically costly and adjusted to paternity risk

“…Although theoretical analyses explicitly assume that there are energetic costs of optimal male time-investment strategies (Andersson 1994), empirical and experimental evidence for this was hitherto non-existent (Partridge & Endler 1987;Arnqvist 1994;Watson & Lighton 1994). Empirical evidence for a trade-o¡ between mate guarding and foraging comes from only three studies, which demonstrated that males increase their mate-guarding time when they are better nourished (the blackbird, Turdus merula (Cuthill & MacDonald 1990); the baboon, Papio cynocephalus (Alberts et al 1996); and the blue milkweed beetle, Chrysochus cobaltinus (Dickinson 1995)). Supportive evidence for the energetic consequences of mate guarding comes from only one study (in rock pipits, Anthus spinoletta), where an observed decrease in foraging and an increase in weight loss of males close to laying was suggested as a means of allocating more time to mate guarding (Askenmo et al 1992).…”

Mate guarding constrains foraging activity of male baboons

“…Recovery of energy reserves and preparation for future mate-guarding episodes no doubt influences mate-guarding behaviour in many species. Among blackbirds, males increase their investment in mate-guarding behaviour when they are better nourished (Cuthill & MacDonald 1990), and among elephants, extreme loss of condition in a given year results in reduced mate guarding in the next year (Poole 1989). Although habitat quality and nutritional status are probably always important for mate guarders, however, we hypothesize that the temporal dispersion of reproduction in non-seasonal breeders puts a premium on minimizing the costs of mate guarding, on evaluating the costs of a current mate-guarding attempt against the ability to invest soon in another attempt, and on evaluating the female's fertility and therefore the potential reproductive risks of not guarding the reproductive female.…”

A distinct reed bunting dawn song and its relation to extrapair paternity

“…In addition, persistent singing takes time and energy (Thomas 2002;Ward et al 2003;Ward & Slater 2005;Hasselquist & Bensch 2008) and increases the risk of being taken by a predator (Møller et al 2006). Despite this, the reed bunting dawn chorus is loud and lasts for about 1 h. Thus only males in good physical condition may maintain a high song rate during this time (Cuthill & MacDonald 1990;Thomas & Cuthill 2002;Barnett & Briskie 2007). A high song rate at dawn could thus be an honest signal towards females, indicating male quality (Otter et al 1997).…”

“…Type III song is mainly produced during the dawn chorus. Song output early in the morning is likely to be an honest signal, indicating a male's physical condition, because the birds could not feed during the night (Cuthill & MacDonald 1990;Thomas & Cuthill 2002;Barnett & Briskie 2007). Studies on various species have found a peak in the dawn song activity or intensity during the fertile period of females (Mace 1987;Eens et al 1994;Welling et al 1995).…”