Breeding success of the goldfinch Carduelis carduelis in orange plantations: the effect of predation and starvation

Abstract

SUMMARYSome aspects of the breeding ecology of the Goldfinch Carduelis carduelis were studied during fifteen years in eastern Spain. Density varied between 0-0.6 breeding pairs per 10 Ha. Egg laying usually lasted from early March to early July. The average number of nesting attempts per pair was 3.1. (range 2-4), and no more than three successful clutches per pair were detected. The mean clutch size was 4.0 eggs in February-March, 4.5 during April-May, and 3.8 during June-July, the difference between the last two periods being significant. The eggs were incubated an average of 13.3 days, and the nestlings remained in the nests a mean of 13.9 days. Breeding success decreased significantly during the season from 80% in FebruaryMarch to 19% in June-July. No nestling starved during February-March but one third of the nestlings starved during the last two periods. Predation was highest during June-July. Each pair laying 3-4 clutches fledged an average of 6.7 (range 0-10) young per year and 59% of all nests produced at least one fledgling.Laying dates and clutch size of the Goldfinch at Sagunto fitted the general trends of starting breeding earlier and laying smaller clutches as the latitude decreases. However, the seasonal pattern of nesting failure was opposite to that described in other habitats. Probable causes are discussed.KEY WORDS: Breeding season, Breeding success, Carduelis carduelis, Causes of nesting failure, Clutch size, Orange groves, Sagunto (East Spain). RESUMENSe presentan los resultados de un estudio sobre la ecología de reproducción del jilguero Carduelis carduelis realizado en cultivos de naranjo en Sagunto (España) durante 15 años. La densidad osciló entre 0 y 6.6 parejas nidificantes por 10 Ha. El período de puesta se extiende, en general, entre primeros de marzo y primeros de Julio. Cada pareja construye una media de 3.1 (rango 2-4) nidos, aunque tres es el máximo si todos tienen éxito. El tamaño medio de puesta es de 4.0 huevos en febrero-marzo, 4.5 en abril-mayo, y 3.8 en junio-julio, siendo significativa la diferencia entre los dos últimos períodos. El período medio de incubación fue de 13.3 días, y los pollos permanecieron en el nido una media de 13.9 días. El éxito reproductor * Departamento de Ecología. Universidad de Valencia. 5(producción de pollos en función del número de huevos) decrece significativamente al avanzar la estación, desde un 80% en febrero-marzo hasta un 19% en junio-julio. Durante febreromarzo no muere ningún pollo por inanición, pero la mortaliadad por esta causa afecta a un tercio de los pollos el resto'de la estación. La predación es más alta durante junio-julio. Las parejas con 3-4 puestas producen una media de 6.7 (rango 0-10) pollos por año. Del 59% de los nidos vuela, al menos, un pollo.El inicio de la estación reproductora y el tamaño de puesta del jilguero en Sagunto están de acuerdo con la tendencia de empezar la nidificación antes y reducir el tamaño de puesta al disminuir la latitud. Sin embargo, el patrón estacional de mortalidad en el nido es opuesto al des...

Seasonal clutch size variation of multi‐brooded bird species: comparisons between breeding season and latitudes

“…The average clutch size of both species varies as the season progresses, and at the end of the breeding season clutch sizes are smaller (Gil-Delgado & Catalá 1989, Gil-Delgado et al 1991. The quadratic equations that were applied show a variation typical of multi-brooded species: the clutch sizes of both Greenfinches and Goldfinches initially increase with a peak in mid-season and then a decline (Fig.…”

“…As the exact number of breeding pairs each year was known (see GilDelgado & Catalá 1989, Gil-Delgado et al 1991, we preferred to use the mean of first clutches. The number of first clutches per year was sometimes less than the number of breeding pairs because a number of nests were predated during the laying period, so the nearest nests were considered to be repeated clutches.…”

“…The sample size differed from year to year, as did the size of the breeding population of both species (e.g. Gil-Delgado & Catalá 1989, Gil-Delgado et al 1991. For Goldfinches only, data from 1985 onwards were used because the Goldfinch population breeding in the plot was too small or absent prior to that (Gil-Delgado et al 1991).…”

“…Gil-Delgado & Catalá 1989, Gil-Delgado et al 1991. For Goldfinches only, data from 1985 onwards were used because the Goldfinch population breeding in the plot was too small or absent prior to that (Gil-Delgado et al 1991). The Goldfinch data from 1993 were also excluded because only one nest was found.…”

“…The Greenfinch Carduelis chloris and Goldfinch C. carduelis populations of these plantations have been studied previously (e.g. Gil-Delgado & Catalá 1989, Gil-Delgado et al 1991. Seeds constitute the main diet of the nestlings for both species (Newton 1972, Cramp & Perrins 1994.…”