Ardeola 49(1), 2002, 97-101

USE OF RECORDER CALLS FOR DETECTING LONG-EARED ASIO OTUS

USO DE RECLAMOS GRABADOS PARA DETECTAR BÚHOS CICOS ASIO OTUS

José Antonio MARTêNEZ*, Íñigo ZUBEROGOITIA**, Jesús COLÁS*** & Javier MACêA****

The songs of many are sexual of each experimental visit (see below) varied signals. They convey information on individual between point-count stations (19 h 25 min to 22 qualities that play a relevant role in advertising h 35 min). The experiment was performed one territory ownership and mate attraction (Gale- time at each site only during rainless and wind- otti & Pavan, 1993; Catchpole & Slater, 1995; less nights. Broadcast stations were located wit- Appleby & Redpath, 1997; Galeotti et al., hin 100 m from the edge of the woodlots. 1997; Galeotti 1998). At the hearing of an in- Each experimental visit to a territory inclu- truder, usually react by delivering territo- ded the following phases: (1) Spontaneous calls rial vocalisations. Accordingly, several studies (SC): starting at dusk and after an initial 2-mi- rely on the use of elicited calls to systemati- nute period, we recorded the following data du- cally obtain data on the relative abundance of ring a 10-min period: date, hour, number of de- owls (e.g. Zuberogoitia & Campos, 1997; Mar- tected owls (observed or heard), sex of the tínez & Zuberogoitia 2000, 2002). Whether this according to its vocalisations (Saurola, 1997), technique is an efficient one for detecting calling rate (number of vocalisations), and ago- Long-eared Owls Asio otus is still a controver- nistic response, if any could be noticed. We sial issue. Viada (1994) succeeded in detecting could distinguish sexes by voice because males individuals over a large area by broadcasting a have a low cooing territorial call whereas fe- pool of male, female and fledgling calls, but males produce a nasal buzzing call (Cramp & Sará & Zanca (1989) and Zuberogoitia & Cam- Simmons, 1980; Mikkola, 1983; Saurola, 1997, pos (1998) found that owls were not responsive Scott, 1997). (2) Playback (PB): immediately to playback. after SC, a territorial intrusion was simulated The aims of this study are (1) to determine if by broadcasting male territorial calls using cas- Long-eared Owls respond to broadcasts of sette players for 10 minutes. The recorded call conspecific calls, (2) to determine if the broad- imitated the rate and number of bouts characte- cast improved our ability to detect owls and ristic for the species (Cramp & Simmons, 1980; (3) to discuss the behavioural response of owls. Mikkola, 1983; Scott, 1997). Broadcast volume The study was conducted at 23 sites (16 point- was adjusted to ensure clear vocal rendition. count stations in Madrid, Central Spain; two in The same data as in SC were recorded, plus la- Valladolid, Central Spain; and five in Barcelona, tency (i.e. time elapsed from the onset of the Eastern Spain). All areas were similar in lands- period to the first vocalisation heard). cape structure and composition (dry cereal cro- Some owls were not detected by their vocal plands with scattered woodlots of Pinus spp. or behaviour but because they wing-clapped or Quercus spp. of small to medium sizes). Experi- flew over the point-count station. Altogether ments were carried out from 2/25/00 to 3/9/00, 21 owls were detected during the initial SC pe- during the courtship period of the owls. The start riod (11 of them being vocally active), while 32

* C/ Juan de la Cierva 42, El Campello, E-03560, Alicante, Spain. e-mail: [email protected] ** Laboratorio de Zoología, Departamento de Zoología y Dinámica Celular , Universidad del País Vasco, Apartado 644, E-48080, Bilbao, Spain. e-mail: [email protected] *** Plaza Jaramiel, 3, 1.o Izqda, E-47013 Valls, Barcelona, Spain. **** C/Número Uno, 3, E-08130 Santa Perpetua de la Moguda, Barcelona, Spain. 98 MARTÍNEZ, J. A., ZUBEROGOITIA, I., COLÁS, J. & MACÍA, J. owls were detected during the playback period Table 2 shows the mean calling rate per 10 (20 of them being vocally active; Table 1). Ho- min of males and females detected in each pe- wever, the difference between the number of riod. To test for differences in the calling rates individuals detected during each survey period between contiguous experimental periods we was only marginally significant (χ2 = 2.6, df = 1, compared the number of calls produced by P = 0.049). Only in two territories were owls vocal owls. Between SC and PB periods, not found at all in spite of territories being oc- males significantly increased their calling rate cupied, as shown by a further survey. It is pos- (t = 1.69, P = 0.022, n = 20), as also females sible that in these territories owls were not vo- did (t = 1.24, P = 0.012, n = 20). Females were cal but they flew silently over the station and more vocally active than males in both periods, went unnoticed by the observers. It is also pos- as shown by the differences in call rates (See sible that owls were far from the area at the Table 2 for means. SC: t = Ð2.78, d.f. = 21, time of the experimental visit or that the point- P = 0.011; PB: t = Ð3,48, d.f. = 18 , P = 0.003). count station was too far away from the territo- As the PB period was performed after the rial core area. SC period, it could be argued that differences in

TABLE 1

Number of Long-eared Owls detected during the two experimental periods at each point-count station. [Número de Búhos Chicos detectados durante los dos periodos experimentales en cada estación de escucha.]

Spontaneous calls [Cantos espontáneos] Playback [Grabación]

Point count Observed Vocal Vocal Observed Vocal Vocal Vocal, sex station + heard males females + heard males females unknown [Estación de [Observados [Machos [Hembras [Observados [Machos [Hembras [Individuos escucha] + oídos] vocales] vocales] + oídos] vocales] vocales] vocales, sexo desco- nocido] 1200411— 2000000— 3100101— 4100201— 5000000— 6200211— 7201211— 8000100— 90001——1 10 0 0 0 0 0 0 — 11 2 1 1 2 0 1 — 12 2 0 1 2 0 1 — 13 2 0 1 2 1 1 — 14 0 0 0 1 1 0 — 15 0 0 0 1 0 0 — 16 0 0 0 1 0 0 — 17 2 0 1 2 1 1 — 18 1 0 1 1 0 0 — 19 1 1 0 1 0 0 — 20 1 0 1 1 0 1 — 21 2 1 1 1 0 0 — 22 0 0 0 1 — — 1 23 0 0 0 2 — — 2 Total 21 3 8 32 6 10 4

Ardeola 49(1), 2002, 97-101 USE OF RECORDER CALLS FOR DETECTING LONG-EARED OWLS ASIO OTUS 99 the number of territories found between the SC lative to the onset of courtship could have been and PB periods could be due to increased spon- small (Martínez & Zuberogoitia, 2000). In that taneous activity of the owls, i.e., our results case, females would spontaneously call to en- would just mirror peaks in hooting. Thus we courage males to provide food (Mikkola, tested if time of the day at which experiments 1983). were conducted had any effect on the probabi- Both males and females increased call rates lity of assessing territory occupancy. First we after the male playback was broadcasted. Ho- tested if calling rates (number of vocalisations wever, the contribution to territorial defence per 10 min) varied with time after dusk, but was quantitatively and qualitatively different we found no significant correlation between between the sexes, males more frequently the time after dusk at which the SC and the PB flying over the experimental station and wing- periods started and calling rates (males: SC: clapping than females, which in turn were more r = 0.33, P = 0.114; PB: r = 0.09, P = 0.693, vocal than males. Of the calling males, 80% n = 23; females: SP: r = 0.36, P = 0.087; PB: also wing-clapped and overflew the experi- r = 0.34, P = 0.123, n = 23; Spearman rank mental station, and 42% kept on doing so after correlations). Then we performed a Logistic the playback was finished. Other than during Regression Analysis (Hosmer & Lemeshow, courtship, Long-eared Owls wing-clap in or- 1989) using the time after dusk as independent der to flush birds and hunt them down (pers. variable and the detection (code 1) or not (code obs.). In order to explain the sex-specific res- 0) of an occupied territory as dependent varia- ponse of Long-eared Owls, we suggest that ble. The probability of detecting a singing some females might have been incubating and Long-eared Owl (i.e., an occupied territory) did that they guarded the nest while the males took not vary with the time after dusk at which the a more active role in territorial defence (Zube- PB periods started (SC: Likelihood Ratio test, rogoitia & Martínez, 2000). One function of 2 G1 = 25.34, P = 0.189). duetting might be to signal an intruder that both Our results suggest that the use of male play- members of the pair will attack together (Ap- backs may increase the chances of detecting pleby et al., 1999). However, we could not find Long-eared Owls during the courtship period. a tendency for members of the pair to respond 48% of the territories would have been wrongly together. This does not necessarily imply that classified as unoccupied if the study had been territorial defence is not cooperative in Long- conducted only by listening to spontaneous vo- eared Owls, such as it is in Scops Owls Otus calisations. Similar results have been found for scops (Galeotti et al., 1997) and Tawny Owls many other owl species (Galeotti 1990; Ward Stix aluco (Appleby et al., 1999). et al.; 1991, Haugh & Didiuk, 1993; Kavanagh Long-eared Owls are monogamous, and ex- & Peake, 1993; Redpath, 1994; Debus, 1995; tra-pair fertilizations are rare (Scott 1997; Zuberogoitia & Campos, 1998). Figure 1 shows Marks et al., 1999). It has been shown that hel- that no new individuals were detected six mi- ping behaviour at nests among related Long- nutes after we started the playback period, alt- eared Owls may occur in stable roosts (Galeot- hough we cannot rule out that a longer period ti et al., 1997). Therefore, it is likely that males for successful detection would emerge if a lar- would benefit from aggressively defending ger sample size was available. Nevertheless, their investment in reproduction against a non- 12 Long-eared Owls were not vocally active related intruder. This could account for the fact in response to playback of conspecifics, and that males responded aggressively to playback. could only be detected by direct observation In conclusion, conducting broadcast surveys while flying over the point-count station or by within three hours of dusk during the late sta- listening to their wing-clapping. ges of courtship or the early days after laying Males, unlike females, were very silent du- should guarantee a sufficient success in asses- ring the SC period. Since the study was perfor- sing territory occupancy. Playback was more med within less than two weeks before the efficient than listening to spontaneous vocali- mean date of laying at every locality (unp. sations in assessing territory occupancy. Ho- data), it is likely that the pair bond was already wever, a high percentage of individuals (mainly established and, therefore, the investment of males) may have gone unnoticed because they males in spontaneous territorial advertising re- did not vocalise in response to playback but

Ardeola 49(1), 2002, 97-101 100 MARTÍNEZ, J. A., ZUBEROGOITIA, I., COLÁS, J. & MACÍA, J.

FIG. 1.—Cumulative response rate of Long-eared Owls during the playback period (number of contacts per station, observed and heard individuals pooled together) in relation to length of the sampling period. [Frecuencia acumulada de contactos de Búhos Chicos vistos u oídos durante el periodo de respuesta a re- clamos grabados con relación a la duración del periodo de muestreo.]

approached the intruder silently or wing-clap- REFERENCES ping. Those individuals may be detected by using a torch (see Martínez & López, 1999). It APPLEBY, B. M. & REDPATH, S. M. 1997. Indicators has been shown that food availability influen- of male quality in the hoots of Tawny owls ces the timing of vocal activity of male Long- aluco. Journal of Raptor Research, 31: 65-70. eared Owls (Tome, 1997). Factors such as ha- APPLEBY, B. M., YAMAGUCHI, N., JOHNSON, P. J. & MCDONALD, D. 1999. Sex-specific territorial res- bitat structure and composition, owl density, ponses in Tawny owls Strix aluco. Ibis, 141: 91- breeding success and the response to playback 99. during migration should also be accounted for CATCHPOLE, C. K. & SLATER, P. J. B. 1995. Bird in order to provide managers with a year-round Songs. Biological Themes and Variations. Cam- labour-efficient survey method. A thorough test bridge University Press. Cambridge. designed to determine the most efficient survey CRAMP, S. & SIMMONS, K. (Eds.) 1980. The Birds of method should also account for the response the Western Paleartic, Vol II. Oxford University of the focal species to a range of stimuli, be- Press. Oxford. cause we cannot be sure that the response to DEBUS, S. J. S. 1995. Surveys of large forest owls in Northern New South Wales: methodology, calling different stimuli be the same (Kroodsma, behaviour and owl responses. Corella, 19: 38-50. 1989). GALEOTTI, P. & PAVAN, C. 1993. Differential res- ponses of territorial twany owls (Strix aluco) to the hooting of neighbours and strangers. Ibis, 135: ACKNOWLEDGMENTS.—We are most indebted to 300-304. members of BRINZAL, Raúl Alonso, Patricia Ore- GALEOTTI, P., SACCHI, R. & PERANI, E. 1997. Coo- jas, Jorge Alonso, Nestor Arenal, Ana Olalla, Laura, perative defence and intrasexual aggression in Eva Saldaña, Julio Yáñez, Mariola Martínez and Sops Owls (Otus scops): responses to playback of Carmen Ruiz who, as usual, did their usual splendid male and female calls. Journal of Raptor Rese- fieldwork. arch, 31: 353-357.

Ardeola 49(1), 2002, 97-101 USE OF RECORDER CALLS FOR DETECTING LONG-EARED OWLS ASIO OTUS 101

GALEOTTI, P. 1998. Correlates of hoot rate and struc- MARTêNEZ, J. A. & ZUBEROGOITIA, I. 2002. Factors ture in male Tawny owls Strix aluco: implications affecting the vocal behaviour of Eagle Owls Bubo for male rivalry and female mate choice. Journal bubo: effects of sex and territorial status. Ardeola, of Avian Biology, 29: 25-32. 49: 000-000. HAUG, E. & DIDIUK A. 1993. Use of recorded calls to MIKKOLA, H. 1993. The Owls of Europe. T. & A. D. detect Burrowing owls. Journal of Field Ornitho- Poyser. Calton. logy, 64: 188-194. REDPATH, S. M. 1994. Censusing Tawny owls Strix HOSMER, D. W. & LEMERSHOW, S. 1989. Applied aluco by the use of imitation calls. Bird Study, Logistic Regression. Wiley & Sons. New York. 41: 192-198. KAVANAGH, R. P. & PEAKE, P. 1993. Survey proce- SAUROLA, P. (Ed..) 1997. Suomen Pöllöt. Kir- dures for nocturnal forest birds: an evaluation of jayhtymä Oy. Helsinki. variability in census due to temporal factors, we- SARÁ, M. & ZANCA, L. 1989. Considerazioni sul cen- ather and technique. In. P. Olsen (Ed.). Austra- simento degli Strigiformi. Rivista. Italiana di Or- lian Raptor Studies, pp. 86-100. Australasian Rap- nitologia, 59 : 3-16. tor Association, R.A.O.U.. Melbourne. SCOTT, D. 1997. The Long-eared Owl. The Hawk KORPIMÄKI, E., LAHTI, K., MAY, C, PARKIN, G, TO- and Owl Trust. London. LONEN, P & WETTON, J. 1996. Copulatory beha- TOME, D. 1997. Timing of territorial vocal activity of viour and paternity determined by DNA finger- the Long-eared Owl (Asio otus) in Slovenia. Ar- print in kestrels: effects of cyclic food abundance. deola, 44: 227-228. Animal Behaviour, 51: 945-955. VIADA, C. 1994. Status y recatalogación del Búho KROODSMA, D. E. 1989. Suggested experimental de- Chico (Asio otus) en Mallorca. Ardeola, 41: 59-62. signs for song playbacks. Animal Behavaviour, WARD, J. P., FRANKLIN, A. B. (GUTIERREZ, R. J. 37: 600-609. 1991. Using search time and regression to esti- MARKS, J. S., DICKINSON, J. L. & HAYDOCK, J. 1999. mate abundance of territorial Spotted-Owls. Eco- Genetic monogamy in Long-eared owls. Condor, logical Applications, 1: 207-214. 101: 854-859. ZUBEROGOITIA I. (CAMPOS, L. F. 1998. Censusing MARTINEZ, J. A. & LÓPEZ, G. 1999. Breeding eco- owls in large areas: a comparison between met- logy of the ( alba) in Valencia (East hods. Ardeola, 45: 47-53. of Spain). Journal für Ornithologie, 140: 93-99. ZUBEROGOITIA, I. & MARTêNEZ. J. A. 2000. Methods MARTINEZ, J. A. & ZUBEROGOITIA, I. 2000. The res- for surveying Tawny Owls Strix aluco in large ponse of the Eagle Owl (Bubo bubo) to an outbre- areas. Biota, 1: 137-146. ak of the rabbit hemorrhagic disease. Journal für Ornithologie, 142: 204-211. [Recibido: 17-9-01] [Aceptado: 19-12-01]

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