Western North American Naturalist
Volume 63 Number 2 Article 8
4-30-2003
Horned Lark (Eremophila alpestris L.) predation on alkali bees, Nomia melanderi Cockerell
Richard W. Rust University of Nevada, Reno
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Recommended Citation Rust, Richard W. (2003) "Horned Lark (Eremophila alpestris L.) predation on alkali bees, Nomia melanderi Cockerell," Western North American Naturalist: Vol. 63 : No. 2 , Article 8. Available at: https://scholarsarchive.byu.edu/wnan/vol63/iss2/8
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HORNED LARK (EREMOPHILA ALPESTRIS L.) PREDATION ON ALKALI BEES, NOMIA MELANDERI COCKERELL
Richard W Rustl
ABSTRACT.-Homed Larks (Eremophila alpestris L.), sampled dUring the first 2 weeks of alkali bee (Nomia T1l£landeri Cockerell) emergence at bee nesting sites in 2 alfalfa seed~growing regions in central Nevada, ate significantly more male than female alkali bees. Exploitation rates suggest that individual Homed Larks consume 10 to 200 alkali bees per day and feed an additional 300 to 1000 bees per day to nestlings.
Key words: predation, Great Basin Desert, alfalfa, insects, bi:rds.
Homed Larks (Eremophila alpestris L.) are summer 2001. The 4 Lovelock sites are nat common, year-round residents of the Great ural and range in size from 1.5 to 3.0 ha; the 4 Basin Desert shadscale community and adja Dixie Valley sites are man-made (Bohart and cent agricultural lands (Behle and Perry 1975, Knowlton 1960, Stephen 1960), adjacent to Ryser 1985, Medin 1986, 1990). They are alfalfa fields, and range in size from 0.16 to 0.5 ground-nesters and forage as ground-gleaning ha. In both locations nonagricultural lands are omnivores (DeGraaf et aI. 1985), feeding on Great Basin shadscale desert (Vankat 1979) seeds in winter months and arthropods and dominated by species ofAtriplex and Sarcoba seeds during the remainder ofthe year (Beason tus (Chenopodiaceae). 1995). Nestlings are fed predominantly arthro I made bird counts at each site upon each pods, especially Lepidoptera larvae and Orthop arrival and scanned the bee-nesting site with tera (Maher 1979). Horned Larks are known binoculars. Nesting sites are free ofvegetation, predators of adult alkali bees (Nomia melan allowing an easy count ofbirds. Birds were shot deri Cockerell; Frick 1962). Alkali bees, a between sunrise and 1200 hours (PST) and western North American species, nest gregari individually bagged and placed on ice for trans ously in soils associated with alkali flats port to the laboratory. (Bohart and Cross 1955, Ribble 1965) and are The digestive tract from oesophagus to effective and efficient pollinators of alfalfa cloaca was removed. I opened the crop and (Medicago sativa L.; Bohart 1957, 1972, Bohart proventriculus (McLelland 1979) and preserved and Koerber 1972), for which they have been the contents in 70% ethanol. Crop and proven utilized and developed (Torchio 1987, Wichelns triculus contents were sorted and items were et al. 1992). identified to sex of alkali bees, with other in Here 1 examine the foraging impact of sects and artbropods identified to order, family, Horned Larks on adult alkali bees as deter and genus where possible. Seeds were sorted mined by digestive tract content analysis and foraging bird densities measured during 2 peri by morphological types. Alkali bee males were ods of adult bee emergence and from 2 loca identified by the presence of their enlarged tions in central Nevada. hind tibiae and females by the pseudopygid ium on the sixth abdominal tergum (Ribble METHODS AND MATERIALS 1965, Stephen et al. 1969). These 2 parts re mained diagnostic despite the grinding action Homed Larks were collected from 4 alkali of the proventriculus. In addition to the above bee nesting sites in the alfalfa-growing regions parts, male genitalia, anterior portions of male of both Lovelock (LL) and Dixie Valley (DV), abdominal sterna 4 and 5, and female antennal Pershing County, Nevada, during the 1st and scapes were found in most stomach contents 2nd weeks of adult alkali bee emergence in containing alkali bees.
lDepartment ofBioJogy, University of Nevada, Reno, NV 89557.
224 2003] HORNED LARK PREDATION ON ALKALI BEES 225
Descriptive statistics and 2-factor analysis difference in the number of larvae taken be ofvariance were employed to test the relation tween the 2 locations (F = 4.33, df = 1,29, P ship between mean birds present and mean = 0.049; LL mean 0.57 + 0.75, range 0-2; DV captures for the 2 locations and sampling peri mean 2.31 + 3.36, range 0-12). There was no ods (Zar 1996). Means + standard deviations significant difference in the mean number taken are presented. Analyses were perfonned in between the 1st and 2nd weeks or the interac Minitab® release 12 (Minitab 1998). tion of location and date (P = 0.09 and P = Horned Larks were removed with permits 0.102, respectively). from the state of Nevada (Scientific Collection Ninety-five percent (18 of 19; LL 9 of 9, Pennit S20567) and Federal Fish and Wildlife DV 9 of 10) ofbirds from the 1st week ofbee (Permit MB042219-0). All birds are deposited emergence contained 1 or more alkali bees, in the ornithological collection at the Univer whereas only 28% (5 of 18; LL 1 of9, DV 4 of sity of Nevada, Reno. 9) of birds from the 2nd week contained alkali bees (Table 1). The distribution of alkali bees RESULTS taken by Horned Larks by location, date, and sex showed that male bees were taken signifi Thirty-nine Horned Larks were obtained. cantly more often than females at both times From Levelock nesting sites, I acquired 2 before (total bees F = 7.28, df = 1,29, P = 0.011; alkali bee emergence (31 May 2001), 9 the 1st male bees F = 6.98, df = 1,29, P = 0.013; week of emergence (12 June 2001), and 9 the Table 1). There were no significant differences 2nd week (19 June 2001). From Dixie Valley in female bees taken between location and sites, 1 acquired 10 during the 1st week ofbee date or the location-date interaction (P = emergence (1 June 2001) and 9 the 2nd week 0.136, P = 0.566, and P = 0.566, respectively; (7 June 2001). 1 obtained an almost equal num Table 1). There were no significant differences ber of males and females (LL 10 males and 10 in total bees, male bees taken by date, or the females, DV 10 males and 9 females). All birds location-date interaction (total bees location had enlarged ovaries or testes and 1 female P = 0.493, interaction P = 0.537, male bees contained developing eggs. location P = 0.697, interaction P = 0.617) Counts of Horned Larks at the nesting sites Two Horned Larks taken prior to alkali bee averaged significantly more during the 1st emergence at Lovelock contained only Cheno week of bee emergence (Fdate = 12.55, df = podiaceae seeds with cotyledons (probably Atri 1,42, P = 0.001; LL 1st week mean 8.2 + 6.7, plex) in their digestive tracts. Fifteen (83%) range 0-20, 2nd week mean 0.7 + 0.5, range Lovelock birds and 16 (84%) Dixie Valley birds 0-1; DV 1st week mean 4.8 + 2.1, range 2--9, contained 1 or more seeds. Fifty-eight percent 2nd week mean 2.5 + 1.6, range 0--5). The of the seeds from Lovelock and 70% from location and date-location interactions were Dixie Valley birds were chenopod (probably not significantly different (P = 0.55 and P = Amplex). The other identifiable seed was alfalfa 0.06). (Medicago sativa). Most chenopod seeds had All birds taken during the 1st and 2nd weeks germinated with cotyledons present. There of alkali bee emergence contained 1 or more was a statistical difference in mean number of arthropods, including spiders (reported as birds seeds taken at both locations (F = 8.93, df = with 1 or more prey items; LL 5 of18, DV 3 of 1,29, P = 0.006) and between the 1st and 2nd 19) and solpugids (LL 1 of 18). Insects were weeks (F = 7.54, df = 1,29, P = 0.01) and the represented by Lepidoptera larvae (LL 6 of location-date interaction (F = 0.025, df = 18, DV 12 of 19), Coleoptera families Cicin 1,29, P = 0.025). Mean seeds taken at LL was dellidae (Cicindella sp.) larvae (LL 2 of 18, DV 19.6 + 21.8, range 0-60, and DV 8.2 + 9.4, 2 of19) and Curculionidae adults (DV 1 of19), range 0-37; 1st week mean was 8.7 ± 10.4, Hemiptera family Lygeaidae adults (LL 1 of range 0--37, and 2nd week 18.9 + 21.6, range 18, DV 6 of 19), Diptera family Bombylidae 0-60. (Beterostylum robustum) adults (LL 2 of 18), and Hymenoptera, other than alkali bees, fam DISCUSSION ily Fonnicidae adults (LL 2 of 18, DV 1 of 19). Only Lepidoptera larvae were in sufficient Horned Larks collected from alkali bee numbers for analysis. There was a significant nesting sites during the first 2 weeks of bee 226 WESTERN NORTH AMERICAN NATURALIST [Volume 63
TABLE 1. Time and location predation by Homed Larks, Erenwphila alpestris, on adult alkali bees, Nanna melanderi, recorded from 2 locations in Nevada. Dates represent the 1st and 2nd weeks of alkali bee emergence in a location. Data are means and standard deviations with ranges given in parentheses. Alkali bee Date Males Females Sex undetennined Thtal Lovelock, NV 12 June 3.0 ± 2.8 0.0 0.3 ± 0.5 3.3 + 2.6 (0-9) (0) (0-1) (0-9) 19 June 0.2± 0.4 0.0 0.0 0.2+0.4 (0-1) (0) (0) (0-1) Dixie Valley, NV 1 June 2.9 ± 2.4 0.1 + 0.3 0.4 + 0.7 3.4 + 2.5 (0-9) (0-1) (0-2) (0-9) 7 June 1.0 ± 2.6 0.2 + 0.4 0.2+ 0.4 1.4 +3.2 (0-8) (0-1) (0-1) (0-10) . emergence (early to mid-June) showed char feed on nectar and may sleep attached to acteristic ground-gleaning omnivorous forag alfalfa plants at night (Bohart and Cross 1955, ing (DeGraafet al. 1985, Beason 1995). Unlike Stephen et al. 1969). Male mating behavior other studies where Hymenoptera represent probably increases their susceptibility to Horned minor portions of Horned Lark diets (Roten Lark or other ground-gleaning bird predation. berry 1980) and food for nestlings (Maher Conservative exploitation rates based on 1979), Lovelock and Dixie Valley birds were the assumption that the observed gut contents exploiting the rich supply of alkali bees, espe represent 1 day's hunting and consumption cially males, during the initial week of bee for the individual and not food for nestlings emergence. This bigh rate of capture decreased (McAtee 1905, Pickwell 1931, Maher 1979) significantly when female bees started to appear suggest that Horned Larks may consume 13 to during the 2nd week of emergence. The non 22 alkali bees per day from a nesting site significant difference between tbe 1st and 2nd (mean bees eaten X mean birds per site) to weeks at Dixie Valley resulted from 1 second perbaps a maximum of200 bees per day (max week bird that bad taken 10 bees (Table 1). imum bees x maximum birds per site). Since Alkali bees are protandrous (Bobart and nothing is known concerning nutritional re Cross 1955) with males appearing approximate quirements (Beason 1995) or daily consumption ly 5 to 7 days before females; botb sexes have rates necessary to maintain energy reserves a 25- to 30-day period of emergence (Stephen that reach lowest levels during incubation and 1965, Mayer and Miliczky 1998). Horned Larks overnight fasting (Swain 1991, 1992), these were apparently "learning" to recognize alkali alkali bee exploitation rates may represent bees and even to discriminate between the minimum values. Tbe removal of 200 bees per sexually dimorphic individuals (Ribble 1965), day to 1400 per week, mostly males, probably avoiding females and their defensive sting in has a minor impact on populations of bees in preference of male bees, which do not possess large natural nesting sites or well-managed a sting apparatus (Michener 2000). Horned artificial sites, where 50 to 200 bees per m2 Larks ate fewer females and fewer total bees bave been estimated (unpublished data). In in the 2nd week of emergence. Male bees smaller or less productive nesting sites, this search for females at the nesting site as females estimated removal could have a major impact emerge (Bohart and Cross 1955, Mayer and on bee populations. However, if predator-prey Miliczky 1998). Males fly over the nesting site functional response concepts (Holling 1959) usually within 10 cm of the surface and are considered, fewer bees will be removed by approach emerging females from upwind. birds in low-density sites. Mayer and Miliczky (1998) report numerous If Horned Larks forage on alkali bees for male approaches and contacts to newly emerg nestling food, then they may bave a large im ing females during the first few minutes they pact on male bee populations. Maher (1979) in are on the surface of the site. Males will leave a 3-year study found Horned Larks to take the nesting site for alfalfa fields where they between 6.3 and 10.0 prey items per hour 2003] HORNED LARK PREDATION ON ALKALI BEES 227
with a median range of 5-9 prey per sample. lands. I also thank J. Young and S. Nowak, The highest percentage of prey changed from USDA, ARS, Western Regional Research Cen Lepidoptera larvae in May (48%) to Orthoptera, ter for Seed Identifications; C. Cripps, Nevada mainly grasshoppers, in July (71%) and August Department ofEnvironmental Protection; and (88%; Maher 1979). Hymenoptera were less A. Gubanich, W Richardson, and S. Vander than 5% in any month. During the first week Wall, University of Nevada, Reno, for review of of alkali bee emergence with mostly males the manuscript. This research was supported emerging, this might equal 2300 to 7000 bees by a grant from the Northwest Alfalfa Seed as nestling food per nesting pair (items per Growers Association and in part by a Specific hour X prey per sample X 15 hours offoraging Cooperative Agreement (#58-5428-9-14) with time X 7 days X 75% average high prey cap the USDA, Agricultural Research Service, Bee ture rate). However, only 1 Homed Lark taken Biology and Systematics Laboratory, Logan,
• in the present study had prey in its beak-a Utah. lepidopteran larva. Presence of the bombylid fly (Heterostylum LITERATURE CITED robustum), a parasite ofalkali bee (Bohart et al. BEASON, R.C. 1995. Homed Lark (Eremophila alpestris). 1960), and larvae ofthe tiger beetle (CicirukUa Birds of North America 195:1-24. sp.), a predator ofalkali bees (Frick 1962), in 4 BEHLE, WI{" AND M.L. PERRY. 1975. Utah birds: checklist, Lovelock and 2 Dixie Valley birds sbows the seasonal and ecological occurrence charts and guides generalist feeding bebavior of larks on the to bird finding. Utah Museum of Natural History, nesting sites. For H. robustum, Frick (1962) University of Utah, Salt Lake City. BOHART, G.E. 1957. Pollination of alfalfa and red clover. recorded similar observations with a higher Annual Review ofEntomology 2:255-380. percentage of flies present in the birds sam ___. 1972, Management of habitats for wild bees, Pro pled, but numbers captured by bird species ceedings of the 3rd Tall Timbers Conference 3: were not given. 253--266. BOHART, G,E., AND E.A. CROSS. 1955. Time relationships in In addition to the bird predators listed by the nest construction and life cycle of the alkali bee. Frick (1962)-blackbirds (species not reported), Annals of the Entomological Society of America 48: American Robin (Thrdus migratorius), English 403-406. Sparrow (Passer domesticus), Horned Lark, BOHART, C.E., AND G.E KNOWLTON. 1960. Managing alkali bees for alfalfa pollination. Utah State University and Black-billed Magpie (Pica pica)-that con Extension Service Leaflet 78:1-8. sume alkali bees, I observed the Sage Sparrow BOHART, G.E., AND T.W KOERBER. 1972. Insects and seed (Amphispiza beUi) and Western Kingbird (7Yrat> production. Seed Biology 3:1-53. nus verticalis) to hunt, capture, and eat alkali BOHART, G.E., WP. STEPHEN, AND RK. EpPLEY. 1960. The bees. Sage Sparrows were present in both biology of Heterostylum robustum (Diptera: Bom byliidae), a parasite of the alkali bee. Annals of the Lovelock and Dixie Valley nest sites, and West Entomological Society ofAmerica 53:425-435. ern Kingbirds were observed on 1 artificial site DEGRAAF; RM., N.C. TiLGHMAN, AND S.H. ANDERSON. in the Lovelock area. A pair of Western King 1985. Foraging guilds of North American birds. birds nesting in a farm storage building were Environmental Management 9:493-536. FRICK, K.E. 1962. Ecological studies on the alkali bee, observed to take many alkali bees, presumably NOrrUa melanderi, and its bombyliid parasite, Bet males, over a 2-week period during alkali bee erostylum robustum, in Washington. Annals of the • emergence. Both Homed Larks and Sage Spar Entomological Society ofAmerica 55:5-15. rows have been observed feeding on alkali HOLLING, C.S, 1959. The components of predation as revealed by a study of small mammal predation on bees in other natural and artificial nesting sites the European pine sawfly. Canadian Entomologist in Nevada alfalfa seed-growing areas near 9U93.-:J2Q. Orovada, Humboldt County, and Baker, White MAHER, WJ. 1979. Nesting diets ofprairie passerine birds Pine County, Nevada. at Matador, Saskatchenwan, Canada. Ibis 121:437-452. MAYER, D.E, AND E.R. MILICZKY. 1998. Emergence, male behavior, and mating in the alkali bee, Nomia melan ACKNOWLEDGMENTS den Cockerell (Hymenoptera: Halictidae). Journal of the Kansas Entomological Society 71:61-68. I thank T Tate-Hall, U.S. Fish and Wildlife McATEE, WL. 1905. The Horned Larks and their relation Service, and S. Albert, Nevada Division of to agriculture. United States Department ofAgricul Wildlife, for expediting the collecting permits; ture Biological Survey Bulletin 23:1-37 MCLELLAND, J. 1979. Digestive system. Pages 69-181 in and A. Brinkerhoff, 1. Brinkerhoff, and M. A.S. King and J. McLelland, editors, Form and func Phillips for permission to hunt on tbeir private tion in birds. Academic Press, San Francisco, CA. 228 WESTERN NORTH AMERICAN NATURALIST [Volume 63
MEDIN, D.E. 1986. Crazing and passerine breeding birds STEPHEN. WP., G.E. BoHAKf, AND P.E TORCHIO. 1969. The in the Great Basi.n low-shrub desert. Creat Basin biology and external morphology of bees. Oregon Naturalist 4$,567-572. State University, Corvallis. . 1990. Binls of a shadscaJe (Ample< e