Breeding ecology of long-tailed tits Aegithalos caudatus in Northwestern Spain: phenology, nest-site selection, nest success and helping behaviour

Authors: Ángel HERNÁNDEZ

E-mail: ahernan@agro.uva.es

Published: Volume 57(2), December 2010. Pages 267-284.

Language: English

Keywords: Aegithalos caudatus, breeding timing, cooperative breeding, long-tailed tit, nest placement and reproductive success.

Summary:

The population density, phenology, nest-site selection, nest success and helping behaviour of breeding long-tailed tits Aegithalos caudatus was studied in NW Spain during 2002-2007. The fieldwork was conducted in an area of 500 ha between Palacio and Pedrún (42º 43’ 26’’ 42º 46’ 15’’ S-N, 5º 29’ 58’’ 5º 30’ 55’’ E-W, 900-1,000 m a.s.l.), in the Torío river valley, León province. Population density was estimated through line transects and mapping. Records of pairs carrying nest material in their bills, building a nest and carrying food in their bills were distributed in 10-day intervals. Nest-site selection was estimated using the Jacobs’ index. To determine nest success, only those found in the early stages of building were considered. To establish provisioning rates, each nest with nestlings was observed for a minimum of 3 h. The number of helpers at each nest each day was deduced from the maximum number of different adults feeding nestlings at the same time, subtracting the two individuals that formed the pair. Population density was c. 6-10 birds/10 ha. Winter flock break-up and pair formation usually occurred from the beginning of February, nest building during 11 March-10 April, laying and incubation during 11-30 April, and the presence of nestlings throughout May. Probably few pairs renested after failing to breed. The most typical habitats in the nest surroundings were hedgerows and oak woods. Two thirds of the nests were built in shrubs and the rest in trees. Rubus brambles were highly preferred plant species for supporting nests. Nest success was very low (c. 18%), and nest failure occurred mainly before hatching due to predation. No cases of helping behaviour were recorded prior to the nestling stage. Cooperative breeding was verified in 60% of the nests, and it occurred in all the habitats and vegetation strata. The final number of helpers per nest was between one and four, usually one or two. Values over 40 visits to the nest in one hour were only recorded when there was at least one helper, and over 50 visits with two or more helpers. In conclusion, (i) optimal habitat conditions for the long-tailed tit were found in the study area; (ii) several characteristics of the observed breeding ecology coincided with those well-described in similar habitats in the UK; (iii) the same determining factors for helping behaviour probably occurred in both locations, with great importance of low breeding success. Research is needed on the social organization and breeding system of this species in more areas in its wide distribution range.

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