278 SHORTCOMMUNICATIONS VOL. 38, NO. 3 j RaptorRes. 38(3):278-282 ¸ 2004 The Raptor Research Foundation, Inc.

PREMIGRATORY COMMUNAL ROOSTS OF THE LESSER IN THE BOREAL SUMMER

PEDRO P. OLEA 1 AND RUBI•N VERA Dpto.de Biologia Molecular y Cienciasdel Medio Ambiente, Faculty of Experimental Sciences, SEK University, CampusSanta Cruz la Real, SegoviaE-40003 Spain

d•GEL DE FRUTOS2 AND HUGO ROBLES Dpto.de Biolo•a ,Fac. de C.C. BiolSgicasy Ambientales, University of Letn, Letn E-2407l Spain

KEYWORDS: LesserKestrel; Falco naumanni;premigratory roosts during the summer in the Palearctic comes from aggregations;communal roosts. Spain and Italy, and consistsof anecdotal records of two roosts(Tejero et al. 1982 and Aparicio1990, respectively) The LesserKestrel (Falconaumanni) is a small migra- and on the monitoring of at four roostsduring a tory breeding in the Palearctic and wintering single summer (Palumbo 1997, Olea 200lb, Ursfia and mainly in Africa (Siegfriedand Skead 1971, Cramp and Tella 2001). Here, we examine the use of communal Simmons 1980). This speciesis consideredto be a threat- roostsby Lesser Kestrelsin northwesternSpain during ened specieslisted as Vulnerable (BirdLife International three summers. We describe roost site characteristics and 2002). Although many aspectsof their breeding biology examine numbers and temporal variation of roosting have been studied (e.g., Negro et al. 1992, Donfizar et al. Lesser . 1993, Hiraldo et al. 1996, Tella et al. 1996a, 1996b, 1997) METHODS there is little known about the post-fledging period of this (but see Bustamanteand Negro 1994, Garcia Communal roosts were located in the province of 2000, Olea 2001a). This period can be particularlycritical Le6n, northwestern Spain, at about 800 m above sea lev- for the survivalof the juvenile falconsbecause recently el, between the towns of Santas Martas and Sahagfin fledged birds have little experience in foraging, and in (42ø25'-42ø17'N, and 5ø23'-5ø06'W; 11.7øGannual mean avoiding predators and human activities (Anders et al. temperature and 486 mm rainfall). The studyarea covers 1998). During the post-fiedging period, Lesser Kestrels 384 km2 devotedto cereal crops.This area wasselected because communal roosting was observed previously seem to increasesignificantly in their abundancein some (Olea 200lb; pers. obs.). In 2002, we documented 23 areas in northern Spain, where breeding populations are breeding pairs of Lesser Kestrelsin the study area. The small or nonexistent (e.g., Llamas et al. 1987, Jubete landscapewas fiat and open, with practicallyno trees. 1997, Romfin 1998, Olea 200lb) and gather in commu- The area is broken up by a number of small seasonal nal roosts (Olea 200lb, Ursfia and Tella 2001). streams flowing in a north-south direction. When this Avian communal roostingis thought to provide surviv- study was conducted, the fields had been partially har- al benefits (Blanco and Tella 1999) in terms of decreased vestedand the area wasmostly dominated by stubbleand risk and increasedforaging efficiency (Beau- fallow fields (74% of the area). The area is also crossed champ 1999). Some evidence also suggeststhat such by a recently-built highway. Roost Site Detection. An effort was made to find all roosts could facilitate social relationshipswith implica- roostsin the study area. We looked for roost sitesbetween nons in the regulation and viability of populations 20-26 August 1998. In 2001 and 2002 the search for (Blanco et al. 1993, Blanco and Tella 1999) and in the roostsbegan on 25 July and 1 July, respectively.We first conservation of some raptor species (Donfizar et al. checked the roosts used by Lesser Kestrel in previous 1996). To manage and conservea bird population, it is years. Next, we searched for new roostsin the area until necessaryto understand the requirements and the lim- the end of the summer. Several observers with binoculars rang factors of a population throughout the annual pe- (8 X) and telescope (20-60 X) were distributedacross the riod (Steenhoff et al. 1984). For Lesser Kestrels, infor- area at the best vantage points. Roostswere located dur- mation on summer communal roostsis incomplete. The ing late afternoon, becauseduring this period the Lesser specieshas been studied during winter in Spanishareas Kestrelstended to gather around "staging" areas near (Negro et al. 1991) as well as in Africa (austral summer; roosts. These aggregationswere fairly conspicuousand easy to detect. From these sites, kestrels progressively Siegfried and Skead 1971, Kopij 2002). To our knowl- moved toward the roost sites about an hour before sun- edge, the only published information on LesserKestrel set. Monitoring of RoostingBirds. We countedbirds at the roostsbetween 26 August and 26 September in 1998 (ev- E-mail address:[email protected] ery 3-7 d, 7 monitoring d), between 25 July and 10 Oc- SEPTEMBER 2004 SHORT COMMUNICATIONS 279

Table 1. Characteristicsof the premigratorycommunal roostsof LesserKestrels during summersof 1998, 2001, and 2002 in northwestern Spain. Study periods: 26 August-8 Septer•nber 1998, 25 July-10 October 2001, and 1 July-9 October 2002.

ROOSTS

C E BLACK SEVERAI, A B LOCUSTS AND D UTILITY F G EVERGREEN PYLONS COMMON POPLAR POI.ES PYLON POPLAR SUBSTRATE O^K (380 kV) PF•R PL2•NT^TION (<45 kV) (380 kV) PL2•N'I^TION Distance to power- 30m (45 0m (380 20m (<45 40m (380 0 (<45kV) 0 (380kV) 40m (<45 line (kV) in m kv) kV) kV) kV) kV)

Max. no. of kestrels 1998 355 (29 Au- 262 (31 Au- 96 (2 Sep- 106 (8 Sep- gust) gust) tember) tember) 2001 200 (12 Au- 750 (31 Au- 27 (31 Au- 7 (6 Sep- 85 (18 Sep- gust) gust) gust) tember) tember) 2002 360 (4 Sep- 641-666 (2 tember) August) tober in 2001 (every 1-17 d, 14 monitoring d) and be- RESULTS tween 1 July and 9 October in 2002 (every 1-11 d, 23 Description of the Roost Sites. In 1998, four commu- monitoring d). In 1998 and 2001, we began to count nal roosts of Lesser Kestrels were found. Roost site A was birds at roostson 26 Augustand 25July,respectively, after the LesserKestrels began using roosts.For this reason, located in a small evergreen oak forest, where LesserKes- in 2002 we initiated monitoring severalweeks before the trels used a group of five scatteredevergreen oaks 5-8 m previous years to determine accurately the date when high, and close to a road (<150 m; see Table 1). Roost Lesser Kestrels started to use the roosts. B, waslocated on three utility pylons (380 kV). More than Except in 1998, we tried to censusLesser Kestrels using 90% of the individualsroosted on a singlepylon. Roost all roosts simultaneously.Only one roost was monitored C was on three trees (two black locusts[Robinia pseudoa- in 1998; in 2001 and 2002, the two largest and more- cacia]and common pear [Pyruscommunis]) 6-7 m high stableroosts were monitored during the entire studype- Roost D was in a poplar (Populussp.) plantation of 612 riod. Observationsites were at ground level and 300-600 m awayfrom the roosts.Individuals were counted using m2 with poplars20-28 m high. binocularsand 20-60X spottingscopes. To avoid bias in All four roostswere in the vicinity of powerlines (<50 the counting between observers,the same personsmon- m), ranging from <45-380 kV (Table 1), where the birds itored the same roosts.Although this does not eliminate grouped, rested and preened before going to the roost. potential biasesamong roosts,counts of Lesser Kestrels The shortest distance between roost sites was 6 km (be- in the roostswere facilitated by their behavior. Specifi- tween roostsA and C), and the longest, 17 km (between cally, before roosting, kestrels perched on powerlines, roosts A and D). where time was spent preening, or bathed in the sand. In 2001, we located four roosts, two of them were the Thus, we believe that the census of kestrels was reliable. same as in 1998 (A and D). The two new roosts were on We counted individuals going to roosts in 2.5-5 min intervals from 30 min before sunset until all individuals electric poles (E on several <45 kV poles and F on 380 entered the roost. The highest evening count was used kV poles). In 2002, LesserKestrels used roostsA and D, as the roost count for that day. In roost A, we censused but in roost A the birds used a larger number of ever- LesserKestrels when perching on powerlinesclose to the green oaks in the forest than in 1998 (see above). smalland scatteredgroup of evergreenoak trees (Quercus Change of Roost Siteswithin the Year. On 10-12 Sep- ilex), which they used as roost sites (Table 1). At this tember 1998 some changesin the roost siteswere ob- roost, birds flew as singles,in pairs, or in small groups served:kestrels stopped using roost B and roost A was from the wires to the trees, but not in the opposite di- moved 0.5-1.5 km from the previousroost location. On rection. This made counting kestrelsrelatively easy. 17-18 September2001, the kestrelsin roost D split into In 2002, we could not obtain accurate counts of Lesser Kestrelsentering one of the roosts on severaloccasions three groups, one stayedin roost D, another moved to (6 of 23 censuses)because roosting activitywas erratic. roost G, and the third group of kestrelsleft and were not Therefore, kestrelswere counted immediatelyfollowing located. In 2002, the kestrelsin roost D split temporally sunrise leaving the roost (from 30 min before sunrise (between27 and 29 August) in three groups,using two until after all the kestrels left the roost). other nearby plantations of poplars (not included in Ta- 280 SHORT COMMUNICATIONS VOL. 38, NO. 3

and 200 birds in roost A (12 August). The number of LesserKestrels decreased markedly after 7 Septemberin • Roost D both roosts. From October, no birds were observed in the 2001 •Roost A roosts.The maximum number of birds summingup both ---e-- Total roosts,simultaneously censused, was 925 (31 August;Fig. la). Two other small roosts (E and F) were used in 2001 (Table 1). 800 In 2002, the first birds using the roostswere observed on 15 July and 18 July in roosts D and A, respectively 600 (Fig. lb). Use of the two roostsby kestrelsthrough time during the post-fledglingperiod differed in 2002. Roost 400 D increasedmarkedly until 2 August (peak = 653 birds), while kestrelsat roostA steadilyincreased until 4 Septem- ber with 360 birds (Fig. lb). No birds were observedin 2O0 roost D on 16 September, while there were no birds in roost A on 3 October. The maximum number of birds, summingup both roosts,was 761 in 2002 (7 August;Fig. Jul 16 Jul 31 Jul 15 Aug 30 Aug 14 Sop 29 Sop lb). RoostingBehavior. During 2001 and 2002, the roosting behavior was different at the two primary roostsobserved (D and A). At roost D, the birds formed generally a cloud-likeflock circlingabove the roostca. 10 rain before e Roost D 2002 •Roost A entering the roost. However, at roost A the birds flew

"-e-' Total directly from powerlines or the ground to roost as sin- gles,in pairs, or in small groups.Lesser Kestrels entered the roosts from sunset until ca. 30 rain later. In 2001, Lesser Kestrels entered the roosts between 3 and 34 rain • 8oo ,• .e'"*' '. . ."*.... * after sunset. In 2002, Lesser Kestrels entered the roosts from 1.3 rain before-23 min after sunset. • 600 , ,,' ',, DISCUSSION •) 400 In the study area, close to 1000 LesserKestrels used communal roostsat some point during the summer.Sim- •;• 200 ilar aggregationshave been found during this period in northeasternSpain (Ursfa and Tella 2001). Becauseour 0 study area had only 23 LesserKestrel breeding pairs in 1 Jul 16 Jul 31 Jul 15 Aug 30 Aug 14 Sep 29 Sep 2002, the large population we found usingroosts in sum- ruer indicates that most birds were adults or juveniles F•gure 1. Seasonalvariation of Lesser Kestrel abun- coming from other areas, as previouslysuggested by oth- dance at roosts A and D, and total number (sum of kes- er authors (Garcia 2000, Ursfa and Tella 2001) and sup- trels using main roostsA and D); in summer of 2001 (a), ported with observationson post-fiedgingdispersal (Olea and summer of 2002 (b). 2001a). In our studyarea, LesserKestrel used the roostsfrom ble 1). Later that year (between29 Augustand 4 Septem- mid-july until late Septemben This temporal pattern dif- ber), roost D was reused. fers somewhatfi'om that found by Ursda and Tella (2001) Roost Dynamics.In 1998, the mean number of Lesser in two roosts in northeastern Spain (Navarra), where Kestrelsin roost A was 320 until 10 Seplcmbcr; this num- birds used the roosts from early June. This difference ber peaked on 29 August,with 355 individuals.The num- could be due to the fact thai the Navarra roosts could be ber of LesserKestrels decreased markedly after 10 Sep- used by the local population during the breeding period, tember (particularlybetween 10-17 September), until 26 contrary to what has been observed in our study area. September, when no individnals were detected at the Another possibleexplanation would be that there are dif- roost. tbrencesin breeding phenology and/or variationsin the The abundance pattern of roosting LesserKestrels at dates of first occupancy of roosts among years. roostsA and D varied between 2001 and 2002. During The number of birds at the roosts increased from mid- 2001, the number of birds in roost D tended to be about Jnly, probablydue to the arrival of post-breedingindivid- three times higher than in roost A (Fig. la). The maxi- uals. The decrease in the number of Lesser Kestrels from mum number of birds in roost D was 750 (31 August), September coincided with the migration to winter quar- SEPTEMBER 2004 SHORT COMMUNICATIONS 281 ters (Bernis 1980), and was consistent with observations (12 000 breeding pairs; BirdLife 2002) gathered in only by Ursfia and Tella (2001). The maximum of birds, sum- four roost sites in this post-fiedgingperiod, suggesting ming up the two larger roostssimultaneously censused, the importance of these sites for conservation (Ursfa wasreached in Augustin both years (Fig. 1). This agrees and Tella 2001). Therefore, we suggestthat further stud- with what has been observed in Navarra (Ursfia and Tella ies are required to identily other areas and roostsused 2001) and Italy (Palumbo 1997). Nevertheless,the date by the Lesscr Kestrel during the post-fiedgingperiod. of the maximum number of birds varied between roosts, Also, the potential role that these areas could bc playing especiallyin 2002 (Fig. lb). The causeof this difference in the ecology and conservation of Lesser Kestrcl popu- between the roosts A and D is not clear, but it could be lations needs to be examined. due to the fact that roost D was censused at sunrise dur- ing 6 d (between27 July and 15 August;Fig. lb). Kopij RESUMEN.--Existepoca informaci6n sobre dormideros (2002) found LesserKestrels arriving to the roostsseveral comunales estivalesde cernicalo primilla (Falconauman- hours after sunset, therefore the number of birds count- hi) en la regi6n Palearctica. Estudiamoslos dormideros ed at sunrisemay be larger than at sunset.If so, the peak comunales de cernlcalo primilla durante los veranos de observed on 2 August could be due to differences in the 1998, 2001, y 2002 en un area agrlcola (384 km• con 23 counting procedures.However, we do not know whether parejas reproductoras) en el noroeste de Espafia. Los Lesser Kestrels arrived after sunset counts at the roosts dormideros se buscaron intensivamente cada afio por we studied, and if that wasso, what fraction of the pop- todo el area de estudio y se registr6 el nfmero de cer- ulation it represented. On the other hand, the observed nicalos primillas que usaron los dormideros. Los dorm•- negativetrend in number of birdsfrom 7 August (count- deros se ubicaron en diferentes substratos, tanto natur- ed at sunrise) was maintained, although the censuses ales (arboles) como artificiales (torres de alta y baja from 15 August were carried out at sunset, suggesting tensi6n). Se localizaron cuatro dormideros de cernlcalo that such potential bias was minimal (Fig. lb). Alterna- primilia en 1998 (96-355 aves), cinco en 2001 (7-750 tively, the different dynamicsof roostsA and D in 2002 aves) y cuatro en 2002 (360-666 aves). Los dos dorm•- could be due to interchange of individuals between deros con mayor nfmero de cernicalosprimillas fueron roosts (individuals at roost D switched to using roost A usados durante los tres aftos de estudio. E1 nfmero max- later during the post-fiedgingperiod; Fig. lb). imo de cernicalosprimilia en los dos dormideros mas Lesser Kcstrels returned to the study area year after grandesfue de 925 avesen 2001 y 761 en 2002. E1 nf- year and were faithful in their use of communal roosts, mero de cernicalosprimillas alcanz6 el maximo en Agos- with two roostsused at least during 3 yr, suggestingthat to, probablemente por la 11egadade individuosde otras this area could be used as a regular premigratory area. areas, y descendi6 en Septiembre, coincidiendo con la Areas occupied by a relativelyhigh post-breedingpopu- migraci6n. La gran concentraci6n de cernicalosy la fi• lation of LesserKestrel, such as our studyarea where the delidad a los lugaresusados como dormideros sugiereun post-breedingnumbers largely exceeds the breedingpop- importante papel de estasareas en la ecologiay conser- ulation, has also been found in northern Spain (Ursfia vaci6n del cernlcalo primilia. and Tella 2001), and this could be the case elsewhere [Traducci6n de los autores] (e.g.,Jubete 1997, Roman 1998). The apparent fidelity to roost sitessuggests an important role for these sum- ACKNOWLEDGMENTS mer areas.Aparicio (1990) and Morton (1992) have sug- We are grateful to Jesfis Fernandez, Rafael Gonzalez, gestedthat food supplyis important during the period Olga Mora, Cristina Trigal, Maria del Carmen Cordero, prior to migration when individualsmolt and fatten, and Soledad, Irene Marcos, Rodolfo Pozuelo, Tania Velasco, may be a critical factor for the survivalof some raptor Enrique Osorio, and FranciscoJ,. Purroy for their help speciesduring dispersal(Newton 1979, KorpimSkiand during the fieldwork. We thank Alvaro de La Puente, Je- sfis Fernandez, and Rafhel Gonzalez, who loaned us their Lagerstr6m1988, Miller et al. 1997). Therefore,the avail- telescopes.Vittorio Baglione and two anonymous refer- ability of areaswith sufticientfood supplyduring this pe- ees provided valuable suggestionson the manuscript riod (e.g., with high densities of Orthoptera, the main Juan Jos6 Prat improved the English. This researchwas food of LesserKestrel; Franco and Andrada 1977,Tejero partially supported by Montele6n-CajaEspafia Founda- 1982; pers. obs.) could be important. In our study area tion. A. de Frutos was financed by a predoctoral fellow- high densitiesof grasshoppersoccur primarily during ship from the University of Le6n. summer, and this resourceis used by the post-breeding LITERATURE CITED Lesser Kestrel population (P. Olea and A. de Frutos un- publ. data), suggestinga role for this area as a premigra- AP•XmC•O,J.M. 1990. Actividad, selecci6ndel m6todo de tory feeding and stagingarea. caza y balance energ6tico diario de Falco naumanm The ca. 1000 Lesser Kestrels counted in our roosts and durante el periodo premigratorio.Ardeola 37:163-178. the ca. 3000 birds found by Urs•a and Tella (2001) in ANDEgS, A.D., J. FAABOgG,AND F.R. THOMPSON. 1998 two roostsin northern Spain, may indicate that a signifi- Post-fiedgingdispersal, habitat use, and home-range cant fraction of the Spanish Lesser Kcstrel population size of juvenile Wood Thrushes. Auk 115:349-358. 282 SHORT COMMUNICATIONS VOL. 38, NO. 3

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Raptor ResearchFoundation, Sevilla,Spain. dades de en la 11anura cerealista del SE de la provincia de Le6n: I Cong.Int. Avesesteparias. Received15 July 2003; accepted26 May 2004 Junta de Castilia y Letn, Letn, Spain. AssociateEditor: Juan jos6 Negro