Yearly and Seasonal Variation of Breeding Parameters in a Declining Multi-Brooded Passerine, the Tree Sparrow

Abstract

A correct timing of breeding is crucial to any bird species. Single-brooded species are adapted to time breeding so that their nestlings are in the nest when food is most plentiful (Lack 1954). In contrast, species that breed more than once per season seem to opt for a different tactic, by maximizing the number of annual broods. In this regard, Lack (1954) suggested that multi-brooded species should lay as soon as conditions permit. This notion was refined by Crick et al. (1993) who argued that multi-brooded species should start laying before the optimal clutch size is largest. Following this reasoning, there should be an increase followed by a decrease in clutch size through the season (Crick et al. 1993). Thus, multi-brooded species seem to opt for a 'quantity over quality' strategy. That is, seasonal productivity of multi-brooded species not only depends on the productivity of each breeding attempt, but also on the number of broods that parents can raise (Crick et al. 1993, Soler et al. 1995, Weggler 2006. It is clear, therefore, that single and multiple breeders differ in their strategies for maximizing fitness (Stearns 1992).Concerning multiple breeders, they must decide how to allocate their reproductive investment between successive breeding attempts (e.g. Robinson et al. 2010). This aspect is interesting because it allows us to obtain valuable information for discerning general (annual) trends on the basis of the outcome of each of Over a five-year period we monitored breeding parameters in a colony of Tree Sparrows Passer montanus in central Spain. This multi-brooded species can raise one to three broods per season. In this study, we analyzed inter-brood variation in reproductive success to infer the existence of seasonal patterns. We also explored inter-annual variation of life-history traits, which is of particular interest in a declining species like the Tree Sparrow. In agreement with our expectation of a multi-brooded species, clutch size showed a quadratic relationship with laying date. We found that the inter-brood interval varied significantly depending on the number of breeding attempts, which suggests that the species may engage in time-saving behaviours as reported for other multibrooded passerines. Nestlings from second broods fledged in better condition than nestlings from first and third broods. Fewer fledglings were produced in third broods than in preceding breeding attempts. The reproductive output of third broods varied to a large extent among years, whereas inter-annual variation was much less marked in first and second broods. Over the years, we also detected a decrease in nestling size (tarsus and wing length), which was consistent among breeding attempts. Finally, the productivity of the colony remained fairly stable over the study period. This pattern contrasts with negative population trends detected by national monitoring programmes. The proximity of wetland habitats in the surroundings of our colony -essential for adequate invertebrates for the chicks -is suggested as a main re...

Spatial and temporal variation in breeding parameters of two south‐temperate populations of House Wrens

“…Clutch sizes of House Wrens at both LE and LZ were weakly correlated with climatic or demographic variables and showed little variation. Some investigators have proposed that multibrooded birds should breed as early as ambient conditions permit, maximizing the number of annual breeding attempts rather than clutch size (Lack , García‐Navas and Sanz , Dunn and Møller ). Therefore, under certain circumstances, producing more broods with fewer nestlings per brood may improve lifetime reproductive success (Hodges et al ).…”

“…Studies of variation of breeding parameters are typically based on a temporal analysis of single populations (Young , Wilson and Arcese , Hušek et al, , Matthysen et al , Boulton et al , García‐Navas and Sanz , Oppel et al , Lany et al ). However, to differentiate the effects of regional and local factors on breeding phenology, neighboring populations with limited interpopulational dispersal need to be compared during the same time period (Finch , Lambrechts et al , Ringsby et al , Moore et al , Caro et al ).…”

Effects of nest-box environment on fledgling success rate and pathogen load

“…Garcia-Navas et al . ( 2010 ) later found that chicks in wood-crete nest boxes were lighter, which could be due to greater transpiration through panting and other mechanisms used for cooling by chicks. Other studies have shown that differences in temperature, as a result of nest-box orientation, also affect occupancy rates (Ardia et al ., 2006 ; Goodenough et al ., 2008 ).…”

Individual variation in parental tradeoffs between the number and size of offspring at the pre‐ and post‐natal stages

“…Seasonal factors such as changing food supply and risk of nest predation may reduce the cost of raising offspring, hence driving multi-brooded individual breeders to adopt different strategies earlier and later in the season (Gil-Delgado et al 2005, Robinson et al 2010, Decker et al 2012, Garc ıa-Navas & Sanz 2012. For example, Horned Larks Eremophila alpestris increase clutch sizes over the course of the breeding season because food supply increases, while the risk of nest predation decreases, with seasonal plant growth (Du et al 2014).…”