Nomadism in Large Falcons: Lessons from the Saker Falcon in Mongolia

NOMADISM IN LARGE FALCONS: LESSONS FROM THE SAKER FALCON IN MONGOLIA DAVID H. E LLIS 1, I GNACY KITOWSKI 2, AND TERRY B. R OUNDY 3 1Institute for Raptor Studies, 3722 E. Defiance Street, Oracle, AZ 85623, USA. E-mail: [email protected] 2Department of Zoology, University of Life Sciences in Lublin, Akademicka 13, 20-950 Lublin, Poland 3602 East 500 South, Bountiful, UT 84010, USA AbstrAct .—Nesting density of saker Falcons ( Falco cherrug ) in some regions of Mongolia were found to fluctuate dramatically over the years. Very few eyries were consistently occupied year after year. these observations suggest that many sakers leave one territory, move long distances, and establish new territories. the most likely explanation for this nomadism is instability of food sources (i.e., regional peaks and valleys in populations of small rodents). Other demographic traits suggesting nomadism include the mid-summer absence of adults in territories occupied earlier in the spring, asynchronous breeding (i.e., a high proportion of late clutches), abandonment of eggs, more frequent use of marginal sites (e.g., ground nests) in zones of high prey density, and, in the long term, low occupancy rates of poor sites. the data for Mongolia suggest that the saker Falcon exhibits partial nomadism when local prey populations fluctuate widely. More severe fluctuations in prey density in Australia favor complete nomadism for some subpopulations of the black Fal - con ( F. subniger ). Wide scale prey crashes and the persistence of alternate prey in the Arctic sel - dom favor nomadism in the Gyrfalcon ( F. rusticolus ). However, the effects of global warming on Gyrfalcon prey are likely to promote nomadism in the future. Received 24 February 2011, accepted 28 June 2011. Ellis , D. H., i. K itOWsKi , AND t. b. r OuNDy . 2011. Nomadism in large falcons: lessons from the saker Falcon in Mongolia. In r. t. Watson, t. J. cade, M. Fuller, G. Hunt, and E. Potapov (Eds.). Gyrfalcons and Ptarmigan in a changing World. the Peregrine Fund, boise, idaho, usA. http://dx.doi.org/10.4080/gpcw.2011.0307 Key words: Demography, Falco cherrug, nomadism, saker. PriOr tO 1970, saker Falcon ( Falco cherrug ) ski (1876 in shagdarsuren 2000) and was fre - records for Mongolia accumulated largely as quently reported in ornithological expeditions incidental observations made along the track thereafter. these early expeditions have been of research expeditions. the saker was first summarized by Piechocki (1983). raptor sur - reported in Mongolia in the travels of Przewal - veys in Mongolia have been summarized by 1 –ELLIS ET AL .– Meyburg and Meyburg (1983). baumgart 2002). in winter, migratory raptors typically (1978, 1980) studied a few pairs of nesting wander in search of food, so in another sense, sakers and shagdarsuren (2000) recounted many raptors are nomadic, at least in winter. other minor efforts to study the species. However, nomadism in birds, as discussed here, involves breeders leaving behind their Extensive and intensive research began in former territory and moving long distances to 1994 (Ellis 2001, 2010) with a Mongolia-wide breed in a new area (Andersson 1980). study of saker ecology. From this work (1994– Potapov et al. (2000, 2001b, 2001c, 2002, 2008), we learned that the species exists in siz - sumiya et al. 2001) conducted radio telemetry able numbers from extreme western to extreme studies of saker home ranges in Mongolia and eastern zones, that it is common in grassland, looked at migratory movements, but these dry steppe, and montane steppe habitat, and efforts shed no light on nomadism of breeding that it is sparsely distributed in forest edge and pairs as described here. Nomadism is most desert habitats. cliff nesting is common, but commonly associated with foragers having a many pairs use trees and many use artificial narrow feeding niche and living in vast arid structures (e.g., powerline support structures: environments. use of many food sources Ellis 2010, Ellis et al. 1997, 2001, Potopov et lessens the need to follow irruptions of a single al. 2001a). prey species, so for most raptors, breeding site fidelity is high. this paper explores unusual demographic fea - tures favoring partial nomadism in saker pop - For raptors, summer nomadism is best known ulations in Mongolia. We also hypothesize for a few species of owls (clark 1975, explanations for more complete nomadism in Parmelee 1992, Hipkiss et al. 2002, Wiggins et the black Falcon ( F. subniger ) and the reported al. 2006) and Falconiformes, such as the lack of nomadism in the Gyrfalcon ( F. rustico - rough-legged Hawk ( Buteo lagopus ) and lus ). some small falcons (Galushin 1974), all of which are dependent on irruptive prey. Most knowledge of raptor population dynam - regional population nadir events (apparently ics is based on eyrie occupancy and productiv - due to non-availability of prey) have been doc - ity levels. Further, most raptor management umented (Whitaker et al. 1996, bechard and decisions for rare raptors are based on the swem 2002). the best example of nomadism assumption that breeding territories are persist - in large falcons is probably the black Falcon, ent. if a territory is vacant, the pair is treated for which whole populations apparently move mathematically as if lost. indeed, the typical from region to region following their prey, response to low prey densities for most raptors which in turn follow the rains (Ferguson-lees is to reproduce poorly, not to emigrate. How - and christie 2001). ever, for nomadic species, site occupancy rates reveal almost nothing about population size. Here we will evaluate trends for saker Falcon For such species, when breeding sites are site occupancy and productivity across Mon - vacant, locally or regionally, the net number of golia. Although Galushin (1974) stated that the birds for that species may not have decreased: saker is not nomadic, and indeed many saker the birds are simply elsewhere. populations may not be nomadic, some previ - ous publications reveal traits that suggest in one sense, all but sessile consumers (and nomadism in the saker. these include studies therefore all raptors) become nomadic when of reproductive performance (Ellis et al. 1996), food is scarce. Nomadism is traditionally char - unusual breeding situations (Ellis et al. 1997), acterized as wide scale movement of a forager and siblicide (Ellis et al. 1999). corollary following its food supply (Allen and saunders work, conducted by biologists financed pri - 2 –SAKER FALCON NOMADISM – marily by the National Avian research center where we did not observe eggs or young, incu - (NArc) of the united Arab Emirates, was bation, brooding, or feeding. We classified a reported in a volume edited by banzragch et al. few situations as former breeding sites: here (2001) and in the newsletter of the Middle East feathers, eggshells, excrement, or skeletal Falcon research Group available online at remains indicated sakers once bred here but www.savethesaker.com. live birds were absent. to avoid unduly inflat - ing territory totals when reporting site occu - pancy, we tallied a new site only if a pair was METHODS found further than 2 km from an old eyrie. the in six expeditions (1994, 1995, 1997, 1998, only exception to this rule was in 2008 when 2000, and 2008), we traversed much of the we found two pairs during the same year steppe and foothill habitat from extreme east - within 2 km of each other. ern to extreme western Mongolia. We did not search the forests of the north-central region Fledging rates were estimated from observa - nor the drier portions of the Gobi Desert in tions of large nestlings (i.e., ≥ 10 days of age) south-central and southwestern Mongolia. or recently fledged juveniles. if, at a site, birds because Mongolia, even today, is largely with - were fledged, we examined the area for excre - out fences (except along the railroads), and ment, prey remains, and molted down to iden - developed roads are very few, we were able to tify the eyrie location. For sites where the course at will across the landscape searching youngest bird was flying well, we would nor - for falcon eyries. Each year, a team of three or mally be uncertain of the number of young four persons in a single 4WD vehicle traversed fledged, so productivity was reported as ≥ n 3,000–5,400 km. (n = the number of fledged young observed). Eyries with eggs or tiny young were counted Although we did not quantitatively measure as being probably successful only if closely prey density on any expedition, we did note attended by an adult; however, we did not use areas of rodent and lagomorph abundance, so information from the early nesting stages in we are able to hypothesize explanations for the estimating the number of young fledged per falcon distribution patterns we observed. eyrie. Data from early in the nesting season were used only in reporting eyrie occupancy Our method during the first two years was to rates, clutch sizes, and eyrie descriptions. drive in a general direction, then divert left and right when likely raptor nesting habitat in 1994–1995, we entered most eyries to appeared on the horizon. in subsequent years, count young, implant Pit tags, take blood we retraced parts of our 1994 and 1995 routes samples, measure nest sites, etc. (Ellis et al. and revisited most sites found in previous 1996). When parents were incubating or expeditions, but we also deviated in search of brooding small young (especially on sunny or additional pairs. snowy days), we often did not enter eyries and thereby avoided jeopardizing progeny. Also, We classed breeding areas as follows: known for electric power poles and towers, we breeding sites were places where eggs or entered only a sample of eyries, and these pri - young (live or dead) were seen or where one or marily to take measurements, which we sub - more adults were observed incubating, brood - sequently used in describing nests on similar ing, or feeding young.

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