Managing for Coyotes to Enhance Waterfowl Production: an Alternative Perspective

The Prairie Pothole Region (PPR) of North America produces about half of the continent's duck population. Predation on hens, young, and eggs severely impacts duck production In the region decreasing fall flights. Recent studies conducted in the region suggest that management efforts to increase duck production need to consider both habitat and predator effects. Research indicates that managing on the landscape level to protect coyotes in s&~cient numbers to exclude red foxes should be encouraged in PPR areas suitable for duck production and where the risks of damage to domestic livestock and other wildlife species ai-e minimal Over thc past centuiy, mlgratoly wate~fowl hunting in North Amenca has undergone a transition fi-om a subsistence activity with recreational overtones to a recreational act~v~ty with subs~stence overtones (USFWS I 986). Concui~ently, hunting of migrato~y watet-fowl has become more intensively managed. S~nce 1948, waterfowl hunting in the United States has been managed on the basis of migrational units, called "Fl.pvaysn (F~gure 1) Lincoln (1 935) classified the migl-ato~y routes across North America ~n to 4 flyways, based on analysis of banded ~ I I -ds and thar movements These flyways, the Pacific, Central, Mlssisslppi, and Atlant~c, correspond to major n?~grat~onal routes followed by millions of waterfowl and other birds (Bellrose 1976) Although the boundar~es between the routes are not exact, and several species of ducks regularly cross from one flyway to another, the 4 flyways serve as administrative units for managing continental wate~fiwl populations. The southweste~n states of Texas, Oklahon~a, and New Mexico are part of the Central Flyway admin~st~-ative unit. In 1985, over 5 million U S. residents spent over 41.7 m ~ l l ~ o n hunter-days in pursuit of waterfowl. During t h ~ s same period, 691,000 Texans spent 4.88 million hunter-days hunting wate~fowl. This figure constitutes over 10% of all days spent hunting watel-fowl In the U.S. during 1985. Total expenditures for migrato~y bird hunting in the U S. during 1985 were $1 .1 b ~ l l ~ o n (USFWS 1988). The Prairie Pothole Region: duck factory for the Southwest The P r a ~ r ~ e Pothole Reg~on (PPR) of North menca (F~gw-e 2) is the primaly breeding ground for many of the wate~~o\vl that ai-e hunted in the Central Flpvay and subsequently winter In Texas. Although the PPR represents only 10% of North America's duck breeding grounds, about half of the continent's ducks fledge there (Smith et a1 1964, Bellrose 1976). Hence, factors aff'ecting duck production in t h ~ s region are of specla1 interest to wate~fowl populations, wildlife managers and to those that paitic~pate In associated recreational activities (Bellrose 1976, Turner et al. 1987, Sargeant et al. 1993). Studies of nestlng ducks conducted in the PPR indicate that duck production has been reduced because of low nesting success attributed to predation on hens, ducklings and eggs (Coward~n et al 1985, Greenwood et al. 1995). Predation severely limits duck production in the region, ultimately affect~ng the slze of the fall flights (Johnson et al 1992) Effects of predator community composition on nest success P r a ~ n e ducks exhibit evolutionary adaptations (large clutches, renesting, antipredator behaviors, and c ~ y p t ~ c coloration) des~gned to minimize the eEects of predation However, alteration of the Figure I . Major watelfowl flyways of North Amel-~ca. Figure 2. The Prairie Pothole Region of North America prairie landscape has resulted in s~gnificant changes m the composition of the predator conununity which can have severe cffects on watc~fowl populat~ons (Sargeant and Ravel~ng 1992). During the past 120 years, the PPR has been transformed from a largely pristine ecosystem to on that is famed intensively (Tu~ner et al. 1987). These changes have contributed to the degradation and eagmentat~on of duck nesting habitat Further, land use changes also have exposed nesting hens, their eggs and ducklings to different types of predator cornmunit~es than exlsted dur~ng pristine times (Cowardin et a1 1983, 1985, Greenwood et al. 1987). Predators that \\!ere coninion and widely d ~ s tributed before settlement of the reglon disappeared from all or most of the area These tnclude the sw~ft fox (Tirilpes velos) and tlic gray \volf (Cnt~is Ilii~lrs). Other specles that we~.e scarce and distr~buted narrowly, such as the raccoon (Pt~ocyoti lolot.), striped skunk (Aleplri/is ttre/~lritis), red fox (V~llpes vr~ipes), and thc coyote (Catiis latrans), clearly benefitted from hah~tat changes in the reglon Sargeant et al. 1984) These "new" niarnmals are the principal predators c~ul.ently aflkcti~ig duck production in the region (Ke~th 196 1 , Johnson and-Sargeant 1977, Sargeant et al. 1993). The red fox has emerged as the major predator aRecting duck product~on, prcylng on both ducks and eggs (Duebbe1-1 and ,L,okernoen 1976, H~gglns 1977, Salpcant et al 1984, Klett et al 1988, Greenwood et al 1995, Sovnda et al. 1995) Recent ev~deiice suggests that coyotes may have less ~mpact on nesting ducks than red foxes, raccoons, and striped skunks (Johnson et al. 1989, Sargeant et al 1984, 1993, Greenwood et al. 1995, Sovada 1995) Factors afTecting predator abundance and distribution in the PPR Major hab~tat changes affecting predator populatrons in the region ~nclude the conversion of wetland/grassland coml)le~es to a~mually-tilled cropland and the establ~slinient of farmsteads w ~ t h assoc~ated windbreaks, food sources, water, and human presence (Sargeant et al. 1993) These changes increased hab~tat structural divers~ty, favoring many predator species More diverse and stable food supplies became available to coyotes, red foxes, and raccoons. However, changes in the abundance of these species, part~cularly the canids, cannot be attributed solely to habitat changes. Extensive killing of predators m the PPR by humans not only resulted in the extirpation of some specles, such as the gray wolf, but probably prevented the expansion of new predator populations for several decades. H ~ g h fur prices prior to the 1940s, coupled with rural res~dents' dislike for predators, held populations at low levels. When fur prices collapsed during the 1940-60s, the animal damage and control-of-d~sease programs resulted in the deaths of tens of thousands of mammalian predators lhese programs, however, failed to reduce red fox populations to low levels, while having a considerable en'ect on coyote abundance, particularly in ~ntcnsivcly fal-rned areas (Adams 196 1) Interspec~lic relat~ons of canids appear to be another dom~nant factor afl'ect~ng the cu~rent d~stribut~on and abundance of the canid species in PPR (Sargeant 1982). Although habitat changes also allowed raccoons to expand thew range, incompatibil~ty with other predator species probably impeded raccoons from expanding their range earlier. Interanti intraspecific prctlator interactions: duck production consequences Predator conunun~ty cornpos~t~on can impact duck nesting success (Sargeant et al. 1993, Greenwood et al 1995, Sovada ct al. 1995) Of pa~-t~culalconsequence to duck product~on In the prair~e potholc reglon are interact~ons between (among) specific predator species Coyotes suppress the abundance of red foxes (Cr~ddlc 1929, Sargcarit 1982, Voight and Earle 1 983, Sargeant et al. 1987, Marr~son et al. 1989) Sargeant et al. ( 1 993) repoi-ted a strong inverse ~.elat~onsh~p bctween coyote and red fox numbers. Circumstant~al cv~dence also suggests that coyotes may suppress raccoon populations In the PPR (Cowan 1973, Stelfox 1 980, Clark et al. 1989, and Sargeani et al. 1993) Coyotes also occasionally prey upon striped skunks (Godin 1982). Several authors have suggested that coyotes can affect the abundance of predators other than red foxes sufficiently to the estent that duck nesting success is enhaced. Howevm, there is little evidence in the literature to support this contention. Klett et d. (1 988) initidly suggested that diRerences in predator communities from east tu west in the PPR, particulmly the cmids, rnay have been the reascm for o h s e n d higher nest success in tvestem portions of the region. Coyotes \vere more cvmmon than red foxes in the tvestem portion of the region than m the east. Greenwvod et al. (1935) and Sovada et al. (1995) attributed d~erences obsemd in nest success between coyote-dominated areas and fosdominated arcas to coyote suppression of red hues. Sovada 'et al. 1935) reported that average nest success in coyote-dominated areas \vas 1 5% highsr than m fox-dominated meas. This dilt'crence ln nest success ts lmportant because thz hrgher rate eucssds nest success thresh~71d le\ els siiggsated by Courird~n et al ( I 985 t for mtiintriining stable populations of severa1 species of dL1bbling Jucks. Greenwcd et ai (1395) cind Soviiii~ et a1 ( 1395) stiggest tti.it, m arcas ivhsre co-.otcs densities are relatively low, coyotes rnabenefit ducks by rerlucmg nest pred'ition b! hses However, in arelis where coyotes are abunilant, thq can prey eutensively on nesting hens and duck nests (Glup md McDaniel 1 988) Management Implications Greenwood et al ! 1335'1 md Sovacid et a! ( 1995) reported a high ciitgee of~.arrat?ility !n nest success among sttidy s~tes md ilmong years. 30th studies alw re~orted that predation u as the cause of most nest Iailures, md predlitor indicss also vaned cunsiiierabl) mong areas and years. These results support Johnson et iil 'S (1983) contention that p&Lor n~unbm i ~ l ~ n e ar not the wle deterrninmt of nest sticcsss Other hctors uIsl> d e c t nest SUCcess. such JS the abiind,ince of b d e r spaies, hhitcit y u s l i ~ mil qii~intie, the abund~nce of uther pred~tcirs SFL'CLZS. and i r ate~?ciwl nest dcnsities. Van'~bility in nsst success among coyotedominr\teci mil tou-dominared arcas indicates that the prcsznce of coyotzs done manot tnsure high nest success ( Sovada et ril 1395). Their tvork kvas conducted iicnng a drought pzriod, pnmaríly on Conservation Reserve Program lands that had b m d e d to perennial grass cover. The additional grmland may have resulted in geater dispersion of b k wsts tvhich reduced heir risk to prdation. The unxight a lw may have contributed to a reduction in duck abundante and nesting eEort (Smith 1969, Krapu et al. 1983). Low nest density may have a positive intluence on nest mccess by rducing predator etficiency (Marshall 1 307, Wsller 1 979, Hill 1984). Long-tem management eEoits desiped to increase duck production must be applid at the l i inkape Ievel in h11 consideratiun of the species' ha hitat requirements, habitat quali ty and qumtib , prabtor composition and abundmce, and predation nsks. Consideration also should be given to encoura;mg sui5cisnt cotote numbers to eucluiie red foues in xeas of the PPR ithere the potsntiai esists to increase duck prcductiun withour constyuence tu d~>mzstic livestwk prcduction ur other ivildlitz ~ ~ ~ i e s f G r m u ~ ~ i r l e r ~ i 1 1935. Sokadast al 19351