! Butll. GCA 9: 19-23, 1992 Mixed breeding pairs of European Stuvnus vulgavis and Stuvnus unicolov Iin the north-east of A. MOTIS

Ten observations of interspecific pairing of the European Starling and the Spotless Starling have been recorded in a sympatric area located in north-east Spain. Five of the cases refer to copulations and five are well-established mixed poirs. At least two of these pairs have produced full-grown chicks. In 70 % of the total cases and 80 % of the well-established pairs the male was a Spotless Starling and the female o European Stoding. These data show that hybridization is possible in nature and that it occurs with some frequency.

Key words: European Starling, vulgaris, Spotless Starling, Sturnus unicolor, hybridization, sympatry.

Anna Motis. Dep. de Biologia (Vertebrats). Facultat de Biologia. Universitat de Barcelona. Avgda. Diagonal 645. 08028 Barcelona. Rebut: 01.03.93; Acceptat: 23.03.93

INTRODUCTION The iwo are closely related, and because of this several attempts at mixed During this century the European Starling breeding in captivity have been made. Ber- Sturnus vulgaris and the Spotless Starling Stur- thold (1971) obtained hybrids but they died nus unicolor have both undergone very im- before fledging, possibly due to congenital portant expansions in their breeding ranges defects. In contrast, more recently Eens et al. (Bernis 1960, Delvingt 196 1 , Berthold (1992) obtained iwo fledglings from iwo 1968, and others). The first sympatric areas mixed broods. Now, the co-existence of the were not formed until the 1970's in the north two species makes it possible to check if of Spain (Motis et al. 1983, Peris et al. interbrLeding exits undir natural conditions. 1 987, Ferrer et al. 1 99 1 ) and more recently new sympatric areas have been found in This article presents some data about the south-east (Cambrony 1990, Kayser discovery of mixed breeding pairs obtained & Rousseau 1992). in one of the sympatric areas. Butii. GCA 9, 1992

MATERIAL AND METHODS male European Starling. Of the five cases of

well-established 8,~airs,in onlv one case was Observations were recorded frorn studies the male a European Starling. rnade in several years (1982-86 and 1988) Of the 790 starling pairs investigated for of the biology of the two species in the species composition during the entire study largest area of syrnpatry, located in Catalo- period, four were mixed. This represents a nia (north-east Spain) (Ferrer et al. 1991).In total of 0.5 % of all pairs in the population this area, where syrnpatry started to occur studied. in 1977 (Mestre 1978), the nest in large colonies rnainly in the roofs of build- ings, and colonies with the two species are DISCUSSION freauent (Motis 19861. 'spec;es identificdtion was carried out These data show the existence of cases using Leitz 1 0x40 binoculars and a Kowa of mate misidentification of fernales, and 20-60x60 telescope and according to Hir- also, that isolating rnechanisrns during pair aldo & Herrera (1974), Svensson (1975) formation do not prevent interbreeding be- and Motis 119841. A~artfrorn the occa- tween the íwo species. In at least five cases sional obseivation of ' copulations, n the I interspecific pa.;ring has occurred, and in other cases (nest-building, feeding chicks, . two of the cases mixed pairs produced full- etc.), the period of observation lasted as ! grown chicks. Also, in Leucate-Plage (south- long as necessary, sornetimes for several east France), a rnixed pair formed of a .male hours or íwo different days, in order to check Spotless Starling and a fernale European that it corresponded with a well-established Starling was found in 1992, although it was pair, breeding in the sarne nest. not known whether breeding was successful or not (Kayser & Rousseau 1992). Therefore,

1 we can conclude that hybridization beíween RESULTS / the two species under natural conditions oc- I curs to a certain degree in the syrnpatric Five of the observations correspond to areas. well-established pairs (Table 1 ). In one of the In contrast to the results obtained by Ber- cases, (Sarroca/9.5.82) a pair with at least thold (1 971), the observation of fledged four full-grown chicks (19-2 1 days old) was chicks, and especially the case of the cap- observed. One of the chicks was cadured tured chick which died three months later, and lived in captivity for three month's with suggest that hybridization may produce no signs of abnormality until its death. This viable individuals, as has also been found young hybrid died, extremely thin, after se- by Eens et al. (1992), who obtained a veral days of bad feeding conditions. young hybrid that died accidentally when it The pair of Maials/20.4.86 was ob- was three and a half rnonths old. served later on in the season. On 10.5.86 It is interesting to note that in most cases one full-grown chick remained in the nest. It the rnale is a Spotless Starling. Sirnilarly, Eens was fed by a fernale European Starling, and et al. (1 992) found in the two captive rnixed a male Spotless Starling was present close broods that male Spotless Starlings attracted to the nest for a few moments during the European Starlings fernales, even when un- observation ~eriodwhich lasted seven hours. mated males of European Starlings were Taking all the observations into consider- present. Likewise, Spotless Starling domin- ation, in 70 % of the cases the pairs were ance has been proved in the syrnpatric areu formed by rnale Spotless Starling and a fe- where this species wins in 69.7 % of the MIxed breeding pairs of Starlings

DATE PLACE PAIR COMPOSITION ACTIVITY

9.5.82 Sarroca male SS - female ES feeding full-grown chicks 41.27N 00.34E 22.4.83 Llardecans male ES - female SS copulating 41.22N 00.33E 11.5.83 Llardecans male ES - female SS building nest 41.22N 00.33E 18.5.83 El Cogul male SS - female ES copulating* 41.28N 00.41E 29.4/1.5.84 Sarroca male SS - female ES male singing fernale in the nest 41.27N 00.34E 2.5.84 Castelldans male ES - female SS copulating 41.30N 00.46E 10.4.86 Aspa male SS - female ES copulating** 41.30N 00.41E 10.4.86 Aspa male SS - female ES copulating** 41.30N 00.41E 20/21.4.86 Maials male SS - female ES building nest 41.22N 00.30E 11.3.88 Aspa male SS - female ES building nest 41.30N 00.41E

*: Both of these were independently paired with individuals of their own species. **: The male is the same in both cases, the females are different.

Table 1. Records of mixed breeding pairs of European and Spotless Starlings (SS: Sturnus unicolor; ES: Sturnus vulgaris).

Taula 1. Observacions de parelles mixtes entre estornell vulgar i estornell negre.

agonistic encounters between males (unpub- ing population studied, 0.49 % (n=607 lished data). This dominance is probably birds observed) and 1 .O2 % (n=98 birds related to the body size, which is slightly captured) had intermediate plurnage charac larger in the Spotless Starling (Motis 1987). ' teristics (unpublished data); it is likely that From now on it will be necessary to they could have been hybrids: examine the occurrence of hybridization be- tween the two species very thoroughly in all the sympatric areas, as mixed breeding RESUM could be even rnore cornrnon than the aforementioned data reveals. Moreover, Parelles mixtes ¿'Estornell vulgar Stur- some individuals are difficult to identify due nus vulgaris i Estornell negre Sturnus uni- to their interrnediate plurnage. In the breed- color al nord-est d'Espanya. Butil. GCA 9,1992

S'han obtingut deu observacions d'apa- unicolor in captivity. Acta Zoologica et Pa- rellaments interespecifics entre /'estornell vul- thologica Ankerpiensia 82: 35-39. gar Sturnus vulgaris i /'estornell negre Sturnus unicolor a I'area de simpatria situada al FEARE, CJ. 1981. The relevance of nord-est de la Peninsula Iberica. Cinc obser- "natural" habitats to starling damage. In vacions són de cbpules i cinc corresponen Thresh, J.M. (Ed.). Pests, Pathogens and a parelles mixtes ben establertes. Almenys Vegetation. p. 393-400. London: Pitrnans. dues d'aquestes parelles mixtes van produir polls volanders. En el 70% del total dels FEARE, CJ. 1 984. The Starling. Oxford: casos i el 80% de les parelles ben establer- Oxford University Press. tes el mascle fou un estornell negre i la femella un estornell vulgar. Aquestes dades FERRER, X., MOTIS, A. & PERIS, SJ. mostren que la hibridació entre les dues es- 1991. Changes in the breeding range of pecies és possible en condicions naturals i Starlings in the lberian Peninsula during the que es dóna amb certa freqüencia. last 30 years: competition as a limiting fac- tor. Journal of Biogeography 1 8: 63 1-636.

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PERIS, SJ., MOTIS, A. & MARTINEZ, A. TAIn, MMJ. 1 973. Winter food and feed- 1987. La distribución del estornino negro ing requirements of the Starling. Study (Sturnus unicolor Ternrn.) y del estornino pinto 20: 226-236.