Lifetime reproductive success and fitness estimates of long-tailed tits in the Rivelin Valley, Sheffield, UK, from 1994-2019

Data was collected following systematic fieldwork protocols from 1994 to 2019. We studied a colour ringed population of 17-72pairs of long-tailed tits from 1994 to 2019 in an approximately 2.5 km2 section of the Rivelin Valley (53°23’N, 1°34’W), Sheffield, UK. The breeding attempts of all individuals in our study population were monitored closely throughout the breeding season. Nests were found by following pairs and subsequently monitored closely (at approximately 2-4 day intervals until they failed or broods fledged. It is estimated that more than 95% of nests within the study site are found each year with undetected nesting attempts typically failing early in the breeding cycle. Life history traits including timing of breeding (i.e. dates of laying, incubation, hatching and fledging, typically recorded ± 1 day), clutch size (n eggs), brood size (n nestlings), and the identity of parents and helpers were recorded. Nestlings in accessible nests were ringed with a unique colour-ring combination and with a British Trust for Ornithology (BTO) ring when 11 days old, and we sexed each individual using molecular techniques from blood samples taken by brachial venepuncture (under Home Office licence). More than 95% of all adults are ringed by the end of each breeding season with a BTO ring and a unique combination of two colour rings. Survival of offspring to 1 year of age was assessed from recruitment into the study population. Some birds (especially females) disperse beyond the boundaries of the study site, but we assume that local recruitment is proportional to brood productivity. We also assume that breeders that disappear from the study site are dead, an assumption validated by a high resighting probability of marked birds. Life history data are entered into an excel spreadsheet on the day of data collection, supervised by Hatchwell. At the end of each season, data are entered into a bespoke Access database that is designed to identify errors of individual identification, timing of events and magnitude of input variables. The dataset provided to the data centre uses data extracted directly from the Access database that has been subjected to quality control at the time of data collection and entry, and by the design of the database itself. See supporting documentation for method for generation of direct, indirect and inclusive fitness data.