Food density, song rate, and body condition in territory-establishing willow warblers (Phylloscopus trochilus)

Abstract

Early-arriving small male willow warblers (Phylloscopus trochilus) in good body condition were relatively successful at defending their territories. Later arriving neighbouring males tended to be larger but had poorer body condition. When males arrived, food resources were limited but increasing. The song rate varied among males during the period before pair formation and was positively correlated with the male body condition index. Song phrase length and song rate decreased after the performance of other activities, which suggests that singing was energy demanding. The sequence of pairing correlated well with male arrival, song rate, and food abundance. Females apparently take food abundance into account when selecting a mate. A model is presented to explain the adaptation of male and female willow warblers to the avaikbility of food resources in time and space and the role of the male in securing a high-quality breeding territory.RCsumC : Les petits miles en bonne condition physique du Pouillot fitis, Phylloscopus trochilus qui arrivent t6t sont relativement efficaces dans la defense de leur territoire. Les miles avoisinants qui arrivent plus tard ont tendance a etre plus gros, mais sont en moins bonne condition physique. A I'arrivCe des miles, les ressources alimentaires sont limitees mais en croissance. La frequence des chants varie chez les miles au cours de la formation des couples et est directement reliee au coefficient d'embonpoint des miles. La longueur des phrases et la frequence des chants diminuent aprks les autres activites, ce qui semble indiquer que l'emission des chants est une activite exigeante du point de vue energktique. La sequence de la formation des couples est en correlation positive avec l'arrivee des miles, la frequence de leurs chants et l'abondance de la nourriture. Les femelles tiennent apparemment compte de l'abondance de la nourriture lors de leur choix d'un partenaire. On trouvera ici un modkle capable d'expliquer l'adaptation des pouillots miles et femelles a la disponibilite des ressources alimentaires dans le temps et dans l'espace et le r61e joue par les miles lors du choix d'un territoire de reproduction de haute qualite. [Traduit par la Redaction]

Competition for early arrival in migratory birds

“…Many studies suggest strong benefits of prior ownership (Krebs 1982; Rohwer 1982; Jakobsson 1988; Bortolotti & Iko 1992; Tobias 1997). In the view of the present model, birds of highest condition arrive first or almost first under very general conditions, and it is then unlikely that late, low quality newcomers can take over their territories (see also Nyström 1997). Challenges might be more likely to be successful in scenarios where the condition‐dependent arrival order includes order reversals, but the prospect of losing a territory might then be sufficient to deter a low‐quality individual from ‘dishonestly’ early arrival, which would again restore honest arrival orders.…”

Singing in the face of death: male banded wrens Thryophilus pleurostictus sing more to playback in their last breeding season

“…Initial playback song rates were unrelated to body condition and may have signalled motivation. In other species, males that are heavier or in better condition also often sing at higher rates (Marchetti 1998; Nystrom 1997) (but see Galeotti et al 1997). Consistent with this, there is a negative relationship between song rate and temperature in cold weather, and food supplementation increases song rate (Gottlander 1987; Reid 1987; Strain & Mumme 1988).…”

“…Song rate is a flexible signal that can indicate motivation, body condition, parasite load, reproductive success, parental care and territory quality in a range of bird species (reviewed in: Vehrencamp 2000; Collins 2004; Searcy & Nowicki 2005). Song rate is positively correlated with male body condition (Nystrom 1997; Marchetti 1998), suggesting that high song rates are costly. Females prefer males that sing at high rates (Collins 2004), and benefit from earlier mating (Hofstad et al 2002), higher quality territories (Hoileitner et al 1995), higher offspring feeding rates (Welling et al 1997), and higher nesting success (Hoileitner et al 1993).…”

Singing as a handicap: the effects of food availability and weather on song output in the Australian reed warbler Acrocephalus australis

“…So far, most studies have assessed male song output by measuring song rate. A positive association between male song rate and pairing or mating success has been reported in studies on sedge warblers Acrocephalus schoenobaenus (Buchanan and Catchpole 1997), willow warblers Phylloscopus trochilus (Radesäter et al 1987, Nyström 1997) and pied flycatchers Ficedula hypoleuca (Alatalo et al 1990), but not in others e.g. stonechats Saxicola torquata (Greig‐Smith 1982) and dunnocks Prunella modularis (Davies and Lundberg 1984).…”