Garrulus glandarius (Ghiandaia)
Descrizione:
La ghiandaia (Garrulus glandarius) è un uccello passeriforme di medie dimensioni appartenente alla famiglia dei Corvidi. È facilmente riconoscibile per il suo piumaggio variegato: corpo rosato-bruno, ali nere con barre bianche e caratteristici specchi alari blu elettrico barrati di nero. Ha un becco robusto, occhi chiari e un volo ondulato. Intelligente e cauta, la ghiandaia è nota per la sua voce forte e sgraziata, ma anche per la sua capacità di imitare i richiami di altri uccelli e persino suoni umani.
Classificazione scientifica:
Dimensioni e Peso:
La ghiandaia misura 32–35 cm di lunghezza, con un’apertura alare di 52–58 cm. Il peso varia tra 140 e 190 grammi. Ha una corporatura robusta, con ali larghe e arrotondate e una coda relativamente lunga.
Habitat:
Specie tipica dei boschi di latifoglie, in particolare querce, ma presente anche in foreste miste, parchi, frutteti e giardini alberati. Vive in tutta Europa, Nord Africa e Asia temperata. In Italia è presente in maniera uniforme, dagli ambienti collinari e montani fino alle pianure alberate. Preferisce zone con abbondanza di copertura arborea e accesso a fonti di cibo variegate.
Comportamento e Abitudini:
La ghiandaia è onnivora e opportunista: la sua dieta comprende insetti, larve, piccoli vertebrati, uova e nidiacei, ma è famosa per la raccolta e l’accumulo di ghiande, da cui deriva il suo nome scientifico ("glandarius"). Può nasconderne centinaia in buche nel terreno o tra le cortecce, contribuendo involontariamente alla diffusione delle querce.
È un uccello territoriale, talvolta sociale, capace di comportamenti cooperativi e forme di apprendimento avanzato. Attiva durante il giorno, emette un tipico richiamo rauco e stridulo, spesso utilizzato come allarme. Il nido viene costruito su alberi, ed è formato da ramoscelli e materiali vegetali. La femmina depone 4–6 uova, incubate per circa 16 giorni.
Pericoli, Nemici e Minacce:
I principali predatori sono rapaci diurni (come astori e poiane), mustelidi, gatti selvatici e serpenti, soprattutto nei confronti di nidiacei e uova. Tuttavia, la ghiandaia è un uccello molto attento e prudente, difficile da sorprendere. Le minacce principali derivano dalla perdita di habitat boschivi, dalla frammentazione ecologica e dall’inquinamento, ma nel complesso la specie risulta resiliente.
Specie Protetta o Minacciata:
La ghiandaia non è minacciata a livello globale e gode di uno stato di conservazione stabile. È protetta in molti paesi europei, inclusa l’Italia, dove la caccia è vietata. Tuttavia, in alcune aree agricole è stata storicamente considerata "nociva" per le predazioni sui nidi di altri uccelli. Studi recenti ne riconoscono l’importanza ecologica, soprattutto come dispensatrice di semi, contribuendo al rinnovamento forestale.
Bibliografia__________________________________________________________________________
Davidson G, Miller R, Loissel E, Cheke LG, Clayton NS. The development of support intuitions and object causality in juvenile Eurasian jays (Garrulus glandarius). Sci Rep. 2017 Jan 5;7:40062. doi: 10.1038/srep40062. Erratum in: Sci Rep. 2017 Feb 24;7:42936. doi: 10.1038/srep42936.
Abstract. Knowledge about the causal relationship between objects has been studied extensively in human infants, and more recently in adult animals using differential looking time experiments. How knowledge about object support develops in non-human animals has yet to be explored. Here, we studied the ontogeny of support relations in Eurasian jays (Garrulus glandarius), a bird species known for its sophisticated cognitive abilities. Using an expectancy violation paradigm, we measured looking time responses to possible and impossible video and image stimuli. We also controlled for experience with different support types to determine whether the emergence of support intuitions is dependent upon specific interactions with objects, or if reasoning develops independently. At age 9 months, birds looked more at a tool moving a piece of cheese that was not in contact than one that was in direct contact. By the age of 6 months, birds that had not experienced string as a support to hold up objects looked more at impossible images with string hanging from below (unsupported), rather than above (supported). The development of support intuitions may be independent of direct experience with specific support, or knowledge gained from interactions with other objects may be generalised across contexts.
Shaw RC, Plotnik JM, Clayton NS. Exclusion in corvids: the performance of food-caching Eurasian jays (Garrulus glandarius). J Comp Psychol. 2013 Nov;127(4):428-35. doi: 10.1037/a0032010.
Abstract. Choice by exclusion involves selecting a rewarded stimulus by rejecting alternatives that are unlikely to be rewarded. It has been proposed that in corvids, exclusion is an adaptive specialization for caching that, together with object permanence and observational spatial memory, enhances a bird's ability to keep track of the contents of caches. Thus, caching species are predicted to perform well in tasks requiring exclusion. We tested this prediction by assessing the performance of Eurasian jays (Garrulus glandarius), a highly specialized cacher, in a two-way object choice task in which food was hidden in 1 of 2 cups. Consistent with the corvids' capacity for observational spatial memory, jays were highly accurate when shown the location of the food reward. However, the jays failed to exclude the empty cup when shown its contents. This failure to select the baited cup when shown the empty cup was possibly due to jays attending to the experimenter's movements and erroneously selecting the empty cup by responding to these local enhancement cues. To date, no corvids have been tested in an auditory two-way object choice task. Testing exclusion in the auditory domain requires that a bird use the noise produced when the baited cup is shaken to locate the reward. Although jays chose the baited cup more frequently than predicted by chance, their performance did not differ from trials controlling for the use of conflicting cues provided by the experimenter. Overall, our results provide little support for the hypothesis that caching has shaped exclusion abilities in corvids.
Zucca, P., Milos, N. & Vallortigara, G. Piagetian object permanence and its development in Eurasian jays (Garrulus glandarius). Anim Cogn 10, 243–258 (2007). https://doi.org/10.1007/s10071-006-0063-2
Abstract. Object permanence in Eurasian jays (Garrulus glandarius) was investigated using a complete version of the Uzgiris and Hunt scale 1. Nine hand-raised jays were studied, divided into two groups according to their different developmental stages (experiment 1, older jays: 2–3 months old, n = 4; experiment 2, younger jays: 15 days old, n = 5). In the first experiment, we investigated whether older jays could achieve piagetian stage 6 of object permanence. Tasks were administered in a fixed sequence (1–15) according to the protocols used in other avian species. The aim of the second experiment was to check whether testing very young jays before their development of “neophobia” could influence the achievement times of piagetian stages. Furthermore, in this experiment tasks were administered randomly to investigate whether the jays’ achievement of stage 6 follows a fixed sequence related to the development of specific cognitive abilities. All jays tested in experiments 1 and 2 fully achieved piagetian stage 6 and no “A not B” errors were observed. Performance on visible displacement tasks was better than performance on invisible ones. The results of experiment 2 show that “neophobia” affected the response of jays in terms of achievement times; the older jays in experiment 1 took longer to pass all the tasks when compared with the younger, less neophobic, jays in experiment 2. With regard to the achieving order, jays followed a fixed sequence of acquisition in experiment 2, even if tasks were administered randomly, with the exception of one subject. The results of these experiments support the idea that piagetian stages of cognitive development exist in avian species and that they progress through relatively fixed sequences.
Miller R, Logan CJ, Lister K, Clayton NS. Eurasian jays do not copy the choices of conspecifics, but they do show evidence of stimulus enhancement. PeerJ. 2016 Dec 1;4:e2746. doi: 10.7717/peerj.2746.
Abstract. Corvids (birds in the crow family) are hypothesised to have a general cognitive tool-kit because they show a wide range of transferrable skills across social, physical and temporal tasks, despite differences in socioecology. However, it is unknown whether relatively asocial corvids differ from social corvids in their use of social information in the context of copying the choices of others, because only one such test has been conducted in a relatively asocial corvid. We investigated whether relatively asocial Eurasian jays (Garrulus glandarius) use social information (i.e., information made available by others). Previous studies have indicated that jays attend to social context in their caching and mate provisioning behaviour; however, it is unknown whether jays copy the choices of others. We tested the jays in two different tasks varying in difficulty, where social corvid species have demonstrated social information use in both tasks. Firstly, an object-dropping task was conducted requiring objects to be dropped down a tube to release a food reward from a collapsible platform, which corvids can learn through explicit training. Only one rook and one New Caledonian crow have learned the task using social information from a demonstrator. Secondly, we tested the birds on a simple colour discrimination task, which should be easy to solve, because it has been shown that corvids can make colour discriminations. Using the same colour discrimination task in a previous study, all common ravens and carrion crows copied the demonstrator. After observing a conspecific demonstrator, none of the jays solved the object-dropping task, though all jays were subsequently able to learn to solve the task in a non-social situation through explicit training, and jays chose the demonstrated colour at chance levels. Our results suggest that social and relatively asocial corvids differ in social information use, indicating that relatively asocial species may have secondarily lost this ability due to lack of selection pressure from an asocial environment.
