Nestlings of most avian species produce faecal sacs, which facilitate the removal of nestlings’ excrements by parents, thereby reducing proliferation of potentially pathogenic microorganisms and/or detectability by predators and parasites. The nest microbial environment that birds experience during early life might also affect their development and thus, faecal sacs facilitating parental removal may be a strategy to decrease bacterial contamination of nests that could harm developing nestlings. Here, we tested this hypothesis by experimentally broken faecal sacs and spreading them in nests of spotless starlings (Sturnus unicolor), thereby avoiding their removal by adults. In accordance with the hypothesis, experimental nests harboured higher bacterial density than control nests. Nestlings in experimental nests were of smaller size (tarsus length) and experienced lower probability of survival (predation) than those in control nests. Moreover, nestlings in experimental nests tended to suffer more from ectoparasites than those in control nests. We discuss the possible pivotal role of bacteria producing chemical volatiles that ectoparasites and predators might use to find avian nests, and that could explain our experimental results in starlings, Ministerio de Ciencia, Innovación y Universidades and European (FEDER) funds (CGL2013-48193-C3-1-P, CGL2017-83103-P), Peer reviewed

Data file includes (i) average values of melanised (M) and non-melanised (NM) feather wear of nestling birds that grew in different nests. The file also included (ii) information of feather mass degradability of nestlings and adult birds from different nests and species estimated as the olipeptide concentration (μg x mL1) of tubes containing 4mL of PBS buffer and a colony Bacillus licheniformis D13 after 21 days of incubation at 37 ºC in constant agitation at 120 rpm in an orbital agitator (VWR, Spain). The third excel sheet contain information of bacterial loads in terms of terms of mesophilic bacteria (TSA), Enterobacteriaceae (HK), Staphylococcus (VJ), and Enterococcus (KF), and average wear of melanised (M) and non-melanised (NM) wing feathers of nestlings that grew in the same nests where bacterial loads were estimated. The last excel file contain information on feather wear of melanised and non-melanised feathers of each sampled nestlings and adult. All these data were collected the Guadix region (southern Spain) and used to perform the statistical analyses in Tables 2 and 3 in Azcárate et al. 2020 (Doi: 10.1111/jav.02320)., This work was supported by the currently named Ministerio de Ciencia, Innovación y Universidades and European (FEDER) funds (CGL2013-48193-C3-1-P, CGL2013-48193-C3-2-P, CGL2013-48193-C3-3-P, CGL2017-83103-P). MAG and SDL were financed by predoctoral contracts (BES-2014-068661, BES-2014-069116) from the Spanish Ministerio de Economía y Competitividad., Peer reviewed

Dataset used in Tomás et al. (2020): (DOI: 10.1111/jav.02427). Data were collected in the Hoya de Guadix in 2012 in spotless starling (Sturnus unicolor) nests in the framework of an experiment to evaluate whether distance to the cavity entrance and nest size influence the risk of ectoparasitism in avian nests. Dataset includes hatching date, brood size, mean nestling body mass, microclimate of the cavity, as well as ectoparasite abundance and distance between the nest and the cavity entrance before and after experimental manipulation., Dataset used in Tomás et al. (2020): (DOI: 10.1111/jav.02427). It contains data collected in Guadix in 2012 in the framework of an experiment to evaluate whether distance to the cavity entrance and nest size influence the risk of ectoparasitism in avian nests., Financial support was provided by grants from Spanish Ministerio de Ciencia e Innovación (MCI) and FEDER (CGL2010-19233-C03-01), from Ministerio de Economía, Industria y Competitividad (CGL2017-89063-P, CGL2017-83103-P), by a predoctoral fellowship from MCI to CRC, by Junta para Ampliación de Estudios programme to MRR, and by Juan de la Cierva and Ramón y Cajal programmes to GT., Peer reviewed

It contains data collected in Guadix, Granada (southeast Spain) in 2019, in the framework of a research to evaluate the effects of chemical and auditory cues of hoopoes (Upupa epops) in repellence and attraction of blood-feeding flies. Dataset includes number of mosquitoes, blackflies and biting midges collected in insect traps in the field in four habitat types and two sampling periods, in relation to different chemical and auditory stimuli derived from nestlings of this bird species., Financial support was provided by grants from the Spanish Ministerio de Economía, Industria y Competitividad (CGL2017-89063-P, CGL2017-83103-P). GT was also supported by the Ramón y Cajal Programme. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI)., Peer reviewed

Data sampled in “Hoya de Guadix”, Granada, Spain, during breeding seasons (March-July) 2016 and 2019., Data file includes information about identity of each sampled starling nestling, the experiment and treatment assigned to them, biometric measurements on day 10 and day 14, and measurements of colour variables. Colour variables include colouration of eggshells (measured as Brightness and Blue-green chroma for eggs laid on the nest where each nestling was born (nest of origin), and the eggs laid on the nest where each nestling grew (nest of rearing)), and colouration of begging related traits (measured as Mean bright, Total hue, UV hue, Yellow-red hue, UV croma, Yellow-red chroma and Carotenoid chroma) for each body part (mouth, flanges and skin). The data set also includes the plasma carotenoid concentration of each sampled nestling., Ester Martínez Renau was financed by a predoctoral contract (PRE2018-085378), while the whole research group received funds from the Spanish Ministerio de Ciencia, Innovacion y Universidades, and European (FEDER) (CGL2017-83103-P)., Peer reviewed

Data file includes information about identity of each sampled individual, the species id, nest type, age, biometric measurements, the mean of the antagonistic halos shown against each 9 indicator bacteria, the antagonistic activity (average values of the width of antagonistic halos (mm) when tested against each of the nine indicator bacteria), the antagonistic range (Shannon index of the antagonistic activity) and the total density of bacteria on the gland., Ester Martínez Renau was financed by a predoctoral contract PRE2018-085378) while the whole research group received funds from the projects CGL2017-83103-P, PID2020-117429GB-C21 and PID2020-117429GB-C22, funded by the Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación/10.13039/501100011033 and by “Fondo Europeo de Desarrollo Regional, a way of making Europe, Peer reviewed

Dataset 1 includes weekly estimations of median, maximum, minimum and range values of temperature and humidity in nest boxes, for three locations, two experimental treatments and in relation to dormice presence in February., Dataset 2 includes daily differences (between 9:00 am and 3:00 am) in temperature and humidity of open nest boxes occupied or not by dormice., Dataset 3 describes Carnus emergence patterns from each sample of nest material, including number of emerged flies (Carnus abundance), date of first emergence and emergence duration., Dataset 4 includes intensity of parasitism suffered by hoopoe nestlings during the breeding season after the experiment, showing number of Carnus, hatching date, brood size and nestling age., The dataset contains data collected in Guadix, Granada (southeast Spain) in 2020, in the framework of a research to evaluate the effects of overwinter occupancy of nest cavities on the incidence of ectoparasitism suffered by hoopoes (Upupa epops) in the next breeding season., The research group benefited from grants CGL2017-83103-P, CGL2017-89063-P, PGC2018-097426-B-C22, and PID2020-117429GB-C21 funded by MCIN/AEI/ 10.13039/501100011033 and by “ERDF A way of making Europe”. AJGN was funded by the Spanish Ministerio de Ciencia, Innovación y Universidades (Programa de Formación de Personal Investigador JAE Intro). GT was supported by the Ramón y Cajal Programme (RYC-2013-13040)., Peer reviewed

Dataset and R scripts used in the manuscript "Environmental factors associated with nesting habits and age shape the composition and connection between skin and uropygial gland microbiomes of birds", currently under review in Journal of Animal Ecology. It includes the R scripts used for data analysis, along with all necessary data to reproduce the results. The study investigates how species, age and environmental factors (nesting habits), influence the microbiota of the uropygial gland (skin and secretion) across 26 bird species, using 16S rRNA amplicon sequencing to characterise bacterial communities., Ester Martínez-Renau was financed by a predoctoral contract (PRE2018-085378) while the whole research group received funds from the projects CGL2017-83103-P, PID2020-117429GB-C21, and PID2020-117429GB-C22, funded by the Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación/10.13039/501100011033., A. ID - Identification name of the fastq files B. Correspondence - Short identification name of the fastq files C. sample_type - Whether the sample is from the uropgyial gland skin or the uropygial secretion D. Species - Host species name E. Ring - Individual ring number for each bird sampled F. Adults_nd_nestl - Whether we've got adult and nestling samples of the same species G. same_indiv_gland_secre - Wether we've got samples of the same individual for both gland skin and uropygial secretion H. Nest - Nest identification I. Locality - Sampling locality J. Nest_type - Whether the sampled species is open-cup nester or cavity-nester K. Age - Whether the bird sampled is an adult or a nestling L. Age_Nest - Combinación of Age and Nest_type columns M. Date - Sampling date N. Tarsus - Tarsus length O. Weight - Weight P. Height gl - Gland height Q. Length gl - Gland length R. Width gl - Gland width, Peer reviewed