BUSCADOR RECOLECTA

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

Sexually selected signals reliably reflect individual phenotypic or genetic quality and, thus, survival prospects of holders. Telomere length is considered a good predictor of life expectancy and, consequently, exploring the links between telomere length and sexually selected traits is much needed to better understand the mechanisms that maintain the honesty of sexual signals. We manipulated the length of throat feathers in spotless starling (Sturnus unicolor) males (a sexually selected signal) before reproduction and explored its effects on telomere shortening and breeding performance in subsequent reproductive events. We did not detect an effect of the feathers clipping manipulation, but males with longer throat feathers before the experiment had shorter telomeres that also shortened more slowly than those of males with shorter throat feathers did. Moreover, length of throat feathers of males before manipulation was positively related to hatching success of second clutches. Thus, correlative but not experimental results support the expected associations between sexually selected signals, telomeres and reproduction. We discuss such results in scenarios of sexual selection where feather length reflects, but does not directly cause, telomere attrition and enhanced reproductive success. Males with longer throat feathers might be older, more experienced males (i.e., with shorter telomeres), able to buffer telomere shortening between reproductive events. Because of the absence of experimental effects, differential incubation effort of females cannot explain the detected association with hatching success, but other sexually selected traits that covary with throat-feather length could be responsible. Exploring those physiological and/or morphological characteristics related to throat-feather length should therefore be the matter of future research, This work was supported by the currently named Ministerio de Ciencia, Innovación y Universidades and European (FEDER) funds (CGL2013-48193-C3-1-P, CGL2017-83103-P, CGL2017-89063-P, CGL2015-65055-P and PGC2018-095704-B-100). MAG was financed by a predoctoral contract (BES-2014-068661) from the Spanish Ministerio de Economía y Competitividad, and GT by the Ramón y Cajal Programme., Reproductive data; Telomere data, 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

Study area and study species The study was conducted during the years 2015, 2016 and 2017 in a south-eastern region of Spain (Hoya de Guadix, 37º15’N, 3º01’W), where nest-boxes attached to tree trunks or walls at 3–4 m above-ground are available for starlings to breed in (for further information on the study area see Soler et al. (2017)). In the studied starling population, the reproductive season starts in early April and most individuals lay a second clutch during May-June. The most common clutch size is 62 plants to the nest, which have been shown to have antimicrobial-beneficial functions4-5 eggs. Here, we will focus on the colouration of the base of the beak, a trait with a more marked sexual differentiation as we can see in its reflectance at different wavelengths (Fig. 1). Fieldwork and experimental procedure In this population, courtship activity (e.g. singing, introducing fresh green plants and feathers in nest boxes) starts in February, more than one month before egg laying (pers. obs.). During this period, some birds roost in nest-boxes and we take advantage ofthis fact for conducting yearly bird trapping sessions in the study area (twice a year between February and mid-March). One hour before dawn, we closed the entrance of all nest boxes in the study area, and immediately after dawn, we captured by hand all individuals found roosting inside. Captured birds were kept individually in clean cotton bags hanging from a stick to keep birds quiet, and were released immediately after sampling. The maximum time that a captured starling was in the bag did never exced three hours. We explored the possible effect of time that birds were kept in the bag on bird colouration and body condition measures of the males that we recaptured by classifying them as being kept in the bag less than 1 hour (N(males) = 10), between 1 and 2 hours (N = 5), and between 2 and 3 hours (N = 7). After controlling for the effect of date of first and last capture, time between captures, treatment and size of throat feathers in the first capture, results showed that retaining time 184 in first captures did not significantly affect blue, red-yellow, or brightness colouration of the beak of males (F1,15 < 2.66, P > 0.124), nor body condition (F1, 10 = 2.19, P = 0.170) in subsequent captures. It neither had any apparent long-term consequences (see Ruiz-Rodríguez et al. (2015)), nor imply apparent negative effects on breeding performance of captured birds (Soler et al. 2008), This work was supported by the currently named Ministerio de Ciencia,es and European (FEDER) funds (GL2013C-48193-C3-1-P, CGL2017-83103-P Innovación Universidad, CGL2017-89063-P). MAG was financed by a predoctoral contract (BES-2014-068661) from the Spanish Ministerio de Economía y Competitividad, and GT by the Ramón y Cajal Programme, Peer reviewed

Avian brood parasites are expected to select host nests according to characteristics that maximize offspring fitness, such as reduced probability of ectoparasitism. Spotless starlings (Sturnus unicolor) lay immaculate blue eggs that sometimes become brownish- spotted due to the activity of the ectoparasitic fly Carnus hemapterus on incubating birds. Therefore, conspecific parasitic females should adaptively avoid nests with spotted eggshells for parasitism. Here, we manipulated perceived risk of ectoparasitism by painting the eggs with either brown spots (similar to those due to ectoparasite activity), or blue spots. A third group of nests was maintained with immaculate eggshells. Nests with non-spotted eggshells showed the highest rate of brood parasitism, while nests with brownish or bluish spots on the eggshells were parasitized at a similar lower rate. These results suggest that brood parasitic females use the presence of spots on the eggshells in their selection of host nests. This study adds to the scarce evidence showing that brood parasitic birds select host nests with low risk of ectoparasitism and demonstrates that colour patterns of the eggshell (i.e. spottiness) of their potential hosts represent a major cue employed to appraise risk of ectoparasitism, Peer reviewed