Il Picchio muratore (Sitta europaea) è un piccolo uccello passeriforme noto per la sua abilità di arrampicarsi agilmente sui tronchi degli alberi, spesso scendendo con la testa rivolta verso il basso, una caratteristica insolita tra gli uccelli. Il suo piumaggio è caratterizzato da una parte superiore grigio-blu, con il ventre e i fianchi di un colore arancio-rossastro. Una striscia nera passa sopra gli occhi, conferendogli un aspetto distinto. Il picchio muratore ha un becco corto, robusto e appuntito, ideale per cercare insetti e semi nelle fessure della corteccia.

Classificazione scientifica:

• Regno: Animalia
• Phylum: Chordata
• Classe: Aves
• Ordine: Passeriformes
• Famiglia: Sittidae
• Genere: Sitta
• Specie: Sitta europaea

Dimensioni e peso: Il picchio muratore è lungo tra 12 e 14 cm, con un'apertura alare di 22-27 cm. Il suo peso varia tra i 17 e i 25 grammi. Ha un corpo compatto e tozzo, caratteristiche che gli conferiscono grande agilità nei movimenti verticali sugli alberi.

Habitat: Il picchio muratore è una specie che si trova prevalentemente nelle foreste di latifoglie e nelle aree boschive mature, ma si adatta anche ai parchi e ai giardini. È distribuito in gran parte dell'Europa e dell'Asia temperata, dove preferisce ambienti con abbondanza di alberi maturi, particolarmente querce, faggi e pini, dove può trovare insetti e costruire nidi nelle cavità naturali degli alberi.

Comportamento e abitudini: Il picchio muratore è noto per la sua capacità di spostarsi su e giù per i tronchi d'albero, un comportamento raro tra gli uccelli. Durante l'estate si nutre principalmente di insetti, mentre in autunno e inverno include nella sua dieta semi e noci, che spesso nasconde in fessure della corteccia per consumarli successivamente. È un uccello territoriale e monogamo; una coppia può restare insieme per diversi anni e difendere il loro territorio durante tutto l'anno. La stagione riproduttiva va da marzo a luglio. Il nido viene costruito in cavità naturali o abbandonate da altri uccelli, e talvolta le aperture vengono sigillate con fango per ridurre la dimensione dell'ingresso e proteggere il nido.

Pericoli, nemici e minacce: I predatori naturali del picchio muratore includono rapaci, piccoli mammiferi predatori e serpenti, che possono predare uova o nidiacei. Tuttavia, le principali minacce per questa specie derivano dalla perdita di habitat causata dalla deforestazione e dalla riduzione di vecchi alberi con cavità adatte per la nidificazione. In alcune regioni, l'urbanizzazione crescente e la rimozione di alberi morti ha ridotto le aree disponibili per la nidificazione.

Specie protetta o minacciata: Il picchio muratore non è attualmente considerato una specie minacciata a livello globale, ma la conservazione delle foreste mature è cruciale per mantenere le sue popolazioni stabili. In alcune regioni europee, è oggetto di progetti di conservazione che mirano a preservare i suoi habitat naturali, soprattutto in aree dove la deforestazione è più intensa.

Bibliografia__________________________________________________________________________

Galván I. Condition-dependence of pheomelanin-based coloration in nuthatches Sitta europaea suggests a detoxifying function: implications for the evolution of juvenile plumage patterns. Sci Rep. 2017 Aug 22;7(1):9138. doi: 10.1038/s41598-017-09771-4.

Abstract. Adult-like juvenile plumage patterns often signal genotypic quality to parents. During adulthood, the same patterns often signal quality to mates. This has led to assume that adult-like juvenile plumage is a developmental consequence of sexual selection operating in adults. Many of these patterns are produced by the pigment pheomelanin, whose synthesis may help remove toxic excess cysteine. Excess cysteine is likely to arise under conditions of relatively low stress, such as those experienced by nestling birds. Thus, adult-like plumage may be advantageous for juveniles if produced by pheomelanin. In the Eurasian nuthatch Sitta europaea, juveniles are sexually dichromatic and identical to adults. Nestling nuthatches in poorer condition develop more intense pheomelanin-based feathers, indicating greater pigment production. The same is not observed in adults. This is contrary to a function related to signaling quality and instead suggests that, at least in the Eurasian nuthatch, adult-like juvenile plumage has evolved because of the detoxifying function of pheomelanin-based pigmentation. Given the prevalence of colors typically conferred by pheomelanin in juvenile plumage patterns, the detoxifying capacity of pheomelanin under low stress levels should be considered as an explanation for the evolution of both adult-like and distinctively juvenile plumage patterns.

Zink RM, Drovetski SV, Rohwer S. Selective neutrality of mitochondrial ND2 sequences, phylogeography and species limits in Sitta europaea. Mol Phylogenet Evol. 2006 Sep;40(3):679-86. doi: 10.1016/j.ympev.2005.11.002. 

Abstract. Variation and geographic differentiation in mitochondrial DNA (mtDNA) was studied in the widespread and phenotypically variable Eurasian nuthatch (Sitta europaea). To assess whether sequences were evolving in a selectively neutral fashion, we used McDonald-Kreitman [Nature 351 (1991) 652] tests and a tree-based method, which suggested that although ND2 sequences are affected by natural selection against slightly deleterious alleles, the effects do not compromise phylogeographic inferences. Three phylogenetic species-level clades of nuthatches were discovered, corresponding to the Caucasus, southern Europe, and northern Europe plus Asia. Unimodal mismatch distributions within each clade suggest that populations have undergone recent growth. A westward range expansion was inferred from the geographic pattern in nucleotide diversity. Although samples were insufficient, it is possible that nuthatches in England and Japan are recently differentiated. Two specimens of the subspecies S. e. arctica formed a sister group to all other S. europaea, differing by ca. 10% uncorrected sequence divergence, pointing the need for additional study of this phenotypically distinct taxon. As with other species, mtDNA data support major phenotypic distinctions, but not subspecies.

Bellamy PE, Brown NJ, Enoksson B, Firbank LG, Fuller RJ, Hinsley SA, Schotman AG. The influences of habitat, landscape structure and climate on local distribution patterns of the nuthatch (Sitta europaea L.). Oecologia. 1998 Jun;115(1-2):127-136. doi: 10.1007/s004420050499. 

Abstract. The nuthatch, Sitta europaea L., is a small (23 g), cavity-nesting woodland bird which, since the 1970s, has been expanding its range in Britain. However, within this range, the species is notably scarce in an area of eastern England. This gap in the species distribution could arise for several reasons including habitat quality, local landscape structure, regional landscape structure and climate. Field surveys and logistic models of breeding nuthatch presence/absence were used to investigate the relative influences of habitat quality, landscape structure and climate on the prevalence of nuthatches in eastern England. Field surveys of woods in the study area indicated that habitat quality was sufficient to support a nuthatch population. A model of habitat occupancy in relation to local landscape structure, developed in the Netherlands, was applied to the study area. The number of breeding pairs predicted for the study area by the model was lower than expected from habitat area alone, suggesting an additional effect of isolation. However, observed numbers were even lower than those predicted by the model. To evaluate the possible roles of climate and large-scale landscape structure on distribution, presence/absence data of breeding nuthatches at the 10-km grid square scale were related to variables describing climate and the amount and dispersion of broadleaved woodland. While climate in the study area appeared suitable, models including landscape variables suggested that the study area as a whole was unlikely to support nuthatches. Although suitable habitat was available, woodland in the study area appeared to be too isolated from surrounding nuthatch populations for colonisation to be successful. This situation may change if current increases in both national and regional populations continue, thus increasing the number of potential colonists reaching the study area.

Bartošová L, Trnka M, Bauer Z, Možný M, Stěpánek P, Zalud Z. Phenological differences among selected residents and long-distance migrant bird species in central Europe. Int J Biometeorol. 2014 Jul;58(5):809-17. doi: 10.1007/s00484-013-0661-z. 

Abstract. The phenological responses to climate of residents and migrants (short- and long-distance) differ. Although few previous studies have focussed on this topic, the agree that changes in phenology are more apparent for residents than for long-distance migrants. We analysed the breeding times of two selected residents (Sitta europaea, Parus major) and one long-distance migrant (Ficedula albicollis) from 1961 to 2007 in central Europe. The timing of the phenophases of all three bird species showed a significant advance to earlier times. Nevertheless, the most marked shift was observed for the long-distance migrant (1.9 days per decade on average in mean laying date with linearity at the 99.9% confidence level). In contrast, the shifts shown by the residents were smaller (1.6 days for S. europaea and 1.5 days for P. major also on average in mean laying date for both, with linearity at the 95% confidence level). Spearman rank correlation coefficients calculated for pairs of phenophases of given bird species in 20-year subsamples (e.g. 1961-1980, 1962-1981) showed higher phenological separation between the residents and the migrant. This separation is most apparent after the 1980s. Thus, our results indicate that the interconnections between the studied phenological stages of the three bird species are becoming weaker.