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Dermestid Beetles Inhabiting Wading-bird Nests in Northeastern US Estuaries
Katharine C. Parsons, Janet E. Yacabucci, Stephanie R. Schmidt, and Neil A. Hurwitz

Northeastern Naturalist, Volume 16, Issue 3 (2009): 415–422

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2009 NORTHEASTERN NATURALIST 16(3):415–422 Dermestid Beetles Inhabiting Wading-bird Nests in Northeastern US Estuaries Katharine C. Parsons1,*, Janet E. Yacabucci1, Stephanie R. Schmidt1, and Neil A. Hurwitz2 Abstract - Ectoparasitism of nesting birds is known to impact reproduction for many species including cavity-nesting swallows and ground-nesting colonial seabirds. Little information is available from wading birds (e.g., herons, egrets, ibises). We documented skin-eating dermestid beetle abundance in 261 wading-bird nests in seven heronries located in northeastern US estuaries during 1991–2000. Beetles were collected after fledglings were no longer using the nest. We examined all twigs and debris for larval and adult beetles, and excavated holes in twigs to count pupating insects. In addition, nest size was evaluated. Dermestes nidum (dermestid beetle) larvae were prominent members of nest faunal communities in all estuaries. We detected no evidence that beetle abundance correlated with wading-bird species, nest reuse, nest substrate species, or nest-collection date. Regression analysis and partial correlation analysis identified nest size, colony, and year as factors showing a signifi- cant relationship with beetle abundance after accounting for all known factors. Introduction Ectoparasitism of nesting birds is known to impact reproduction for many species, and has been intensively studied in colonially nesting swallows (Brown and Brown 1986, Brown et al. 1995, Hoogland and Sherman 1976) and other cavity-nesting species (Heeb et al. 2000, Wittman and Beason 1992). In addition, some studies have shown ground-nesting seabirds to be impacted by ectoparasites (Duffy 1983, Feare 1976, King et al. 1977). Little information is available for tree-nesting colonial species, yet the potential for significant effects may be high as a result of their coloniality. Snyder et al. (1984) documented dermal lesions on nestlings and dermestid beetles in the nests of Rostrhamus sociabilis Vieillot (Snail Kite), Mycteria americana L. (Wood Stork), and Ardea herodias L. (Great Blue Heron). Studies on wading birds did not quantify beetle abundance or reproductive endpoints associated with beetles or lesions. We investigated the occurrence of dermestid beetles in wading-bird nests at colony-sites in several northeastern US estuaries from 1991– 2000. Our objectives were to quantify the occurrence of dermestid beetles in the nests of wading-bird species and to identify factors influencing beetle abundance. 1Manomet Center for Conservation Sciences, 81 Stage Point Road, PO Box 1770, Manomet, MA 02345-1770. 2Customer Chemistry, DHSoft Tchnologies, Inc., Herndon, VA 20171. *Corresponding author - parsonsk@manomet.org. 416 Northeastern Naturalist Vol. 16, No. 3 Methods Study area During 1991 - 2000, we documented dermestid abundance in wadingbird nests from seven heronries located in: Rehoboth Bay, DE (38°38'N, 75°07'W); Delaware Bay, DE (39°35'N, 75°34'W); New York Harbor, NY (40°34'N, 74°12'W); Cape Cod, MA (41°37'N, 70°25'W); Nantucket, MA (41°17’N, 70°06'W); and Boston Harbor, MA (42°19'N, 70°56'W). All nest studies were conducted under appropriate federal and state scientific collecting permits. All nests collected from Middle Island (Rehoboth Bay) were removed from a stand of Phragmites australis (Cav.) Trin. ex Steud. (Common Reed). At Pea Patch Island (Delaware Bay), nests were collected from Common Reed, Juniperus virginiana L. (Eastern Redcedar), a number of deciduous tree species (Prunus serotina Ehrh. [Black Cherry], Liquidambar styraciflua L. [Sweetgum], Nyssa sylvatica Marsh. [Blackgum], Quercus spp. [oaks], Acer spp. [maples]) and Vaccinium corymbosum L. (Highbush Blueberry). Nests collected from Prall’s Island (New York Harbor) were removed from Betula populifolia Marsh. (Grey Birch). All nests collected in Massachusetts were removed from Eastern Redcedar, except on Gallop’s Island (Boston Harbor), where all nests were removed from a Forsythia sp. (forsythia) hedge. Additional information on study sites may be found in Parsons et al. (2000, 2001). Precipitation data for colony-sites were obtained from the National Climatic Data Center of the National Oceanic and Atmospheric Administration (http://climvis.ncdc.noaa.gov). Total precipitation measured at the nearest weather station was summed for April–July for each colony-year. Nest and beetle surveys Nests selected for examination of nest fauna were an opportunistic subsample of nests randomly selected from the colony as a whole to assess wading-bird productivity (Parsons et al. 2001). All nests collected had contained nestlings, and all were within 4 m of the ground. We recorded when nests were pre-existing from previous years at all sites in years 1995–1996, and at Prall’s Island in 1992 and Sampson’s Island in 1993. Nest fauna were collected after fledglings were no longer using the nests. A drop cloth was placed under the nest, and the entire nest removed from the nest substrate and placed in a plastic bag and sealed. We examined all twigs and debris for larval and adult beetles (>1 mm) and excavated all holes in twigs for pupating insects. As an index of nest size, we counted twigs from 45 dismantled nests. We selected a sample of Bubulcus ibis L. (Cattle Egret) nests on Pea Patch Island (Delaware Bay) to examine within-season temporal patterns in dermestid abundance in 1998. We collected 7 nests at hatching and 6 nests when nestlings were two weeks old. Collected nests were processed as above and were replaced with artificial nests in the colony to allow 2009 K.C. Parsons, J.E. Yacabucci, S.R. Schmidt, and N.A. Hurwitz 417 nesting to continue. An additional 13 nests were collected after nestlings had fledged. We determined the number of dermestids in nests in all years of our study. Dermestids from all sites were collected for identification. Approximately ten live larvae from Sampson’s Island were provided to the University of Massachusetts Cranberry Experiment Station (Wareham, MA), where they were allowed to mature to adults and identified. In addition, we provided approximately 25 beetle adults and larvae from Pea Patch Island preserved in 95% ethyl alcohol to the USDA Systematic Entomology Laboratory (Washington, DC) for identification. Statistical analyses We examined all datasets for compliance with the assumptions of parametric analysis (Shapiro-Wilk’s test; Levene’s test). Square root transformations stabilized heteroscedasticity in dermestid abundance data in some instances; in other cases, data were ranked. We performed a linear regression analysis to examine explanatory factors of nest beetle abundance when viewed in collaboration with each other. Potential factors considered were: nest size, existing/new nest, nesting species, colony, tree type (i.e., deciduous, coniferous, etc.), precipitation, and year. We then ran partial correlations between each of the variables in the final regression model and beetle abundance (square root transformation), conditioned on the remaining significant model variables. The Spearman partial rank order statistic was computed for each variable this way to show the strength of the relationships. All analyses were performed with SAS Version 9.1 (SAS Institute 2003). Where means are reported, they are presented as + 1SD. Results Over the ten-year study, we characterized the presence of dermestid beetles in 261 wading-bird nests including 14 Egretta thula Molina (Snowy Egret), 3 E. caerulea L. (Little Blue Heron), 118 Cattle Egret, 125 Nycticorax nycticorax L. (Black-crowned Night-Heron), and 1 Plegadis falcinellus L. (Glossy Ibis) nests. Wading-bird nests were consistently populated with dermestid beetles (Dermestes sp.); 90% of nests contained beetles and/or shed cuticles (i.e., evidence of beetle activity). Larval and/or adult beetles were documented in 82% of study nests. No individuals of recognized avian ectoparasites (such as Protocalliphora spp. [blowflies]; see review in Waldbauer 1998) other than the hemiparasitic dermestid beetles were detected in the nests. Dermestid beetles were present in wading-bird nests at every site (Table 1). Mean number of dermestids ranged from 0.1 to 83 beetles per nest. Most sample populations were right-skewed, indicating that the majority of nests had small numbers of dermestids and a few nests had large numbers. The maximum number recorded in one nest was 299. Entomologists at the University of Massachusetts Cranberry Experiment Station determined that specimens from Cape Cod nests were of a single 418 Northeastern Naturalist Vol. 16, No. 3 species limited to six possibilities: D. caninus var nubipennis Casey, D. carnivorus Fabricius, D. frischi Kugelann, D. nidum Arrow, D. cadaverinus Fabricius, of D. peruvianus Castelnau (M. Averill, University of Massachusetts Cranberry Experiment Station, Wareham, MA, pers. comm.). The USDA Systematic Entomology Laboratory determined specimens collected from Pea Patch Island to be D. nidum (N. Vandenberg, USDA Systematic Entomology Laboratory, Beltsville, MD, pers. comm.). Voucher specimens of adults and larvae have been placed in the US National Collection (USDA Agricultural Research Service, Beltsville, MD) Using the square root of beetle abundance taken as the dependent variable, nest size, colony, and year all were identified as significant factors. Precipitation showed a strong negative correlation (r = 0.74, P = 0.038) with beetle abundance when viewed by itself (Fig. 1), but was not statistically significant when taking into account all other factors. The best model showed that larger nests contained more beetles, the Sampsons Island colony nests tended to have more beetles than nests in other colonies, and significant inter-year variation in beetle abundance was present. Spearman partial rank order statistics were as follows: nest size (rs = 0.31, P < 0.001); Sampsons Island colony (rs = 0.46, P < 0.001); year-1993 (rs = 0.26, P < 0.001); year- 1995 (rs = 0.62, P < 0.001); year-1997 (rs = 0.41, P = 0.001); year-1998 (rs = 0.35, P < 0.001). Table 1. Occurrence of dermestid beetles in wading-bird nests at colony sites in northeastern US estuaries, 1991–2000. All nests were collected after fledging. Given are mean, SD (n nests), range, and median beetles per nest. Also given are skewness index and results of Shapiro-Wilks test for normality (S-W; P). Colony Year Dermestids Range Median Skewness S-W P Middle Island, 1996 2.0 ± 2.4 (8) 0–6 1 0.9 0.82 0.05 Rehoboth Bay, DE 1997 32.0 ± 48.9 (8) 1–147 11 2.3 0.68 0.001 Pea Patch Island, 1993 36.3 ± 59.3 (15) 0–171 8 1.8 0.65 <0.001 Delaware Bay, DE 1995 50.0 ± 57.5 (31) 0–284 46 2.5 0.75 <0.001 1996 2.2 ± 3.0 (30) 0–11 1 1.5 0.76 <0.001 1997 19.0 ± 20.6 (37) 0–102 12 2.3 0.75 <0.001 1998 15.5 ± 16.5 (30) 0–61 10 1.2 0.85 0.001 2000 5.4 ± 4.1 (5) 0–9 8 -0.7 0.82 0.12 Prall’s Island, 1992 9.1 ± 6.1 (7) 0–18 10 -0.1 0.96 0.83 New York Harbor, NY Sampson’s Island, 1991 26.8 ± 23.2 (4) 11–61 17.5 1.8 0.78 0.07 Cape Cod, MA 1992 45.0 ± 42.6 (13) 1–141 33 1.2 0.86 0.04 1993 74.2 ± 52.2 (9) 7–143 60 0.1 0.91 0.32 Coatue, 1992 2.4 ± 2.3 (5) 0–6 2 1.0 0.94 0.69 Nantucket, MA 1995 22.8 ± 15.5 (8) 8–52 17.5 1.1 0.88 0.18 1996 2.5 ± 6.9 (24) 0–30 0 3.5 0.40 <0.001 Sarah Island, 1995 82.9 ± 98.7 (7) 17–299 56 2.3 0.69 0.003 Boston Harbor, MA Gallops Island, 1992 0.1 ± 0.4 (7) 0–1 0 2.6 0.45 <0.001 Boston Harbor, MA 2009 K.C. Parsons, J.E. Yacabucci, S.R. Schmidt, and N.A. Hurwitz 419 In addition, nests collected throughout the nesting season on Pea Patch Island in 1998 provided no evidence that early (mean collection date [Julian] = 155.3 ± 4.7; n = 7 nests), mid-season (162.5 ± 2.7; n = 6 nests), and late (218.3 ± 5.0; n = 13 nests) dermestid populations differed among seasons (ranked ANOVA: F2,23 = 2.1; P = 0.15). Discussion During a ten-year study, we quantified the abundance of dermestid beetles inhabiting wading-bird nests in colonies located in six estuaries in the northeastern US. Dermestids were found in nests from all estuaries and ranged from 0–299 beetles/nest. Anecdotal reports spanning nearly a century similarly identify dermestid beetles as important members of wading-bird nest faunal communities (see bibliography in Hicks 1959, Jewell 1987, Rodgers et al. 1993, Snyder et al. 1984). No other known avian ectoparasites were detected in nests in the current study nor quantified in previous studies. D. nidum was identified as the dermestid species occupying nests in Delaware Bay, and was included among six possible Dermestes species representing the single dermestid species found in Cape Cod nests. All previous examinations of colonial waterbird nest fauna have identified Figure 1. Precipitation and average dermestid beetle abundance in wading-bird nests from colonies in northeastern US estuaries, 1992–1998. Shown are mean (square root transformed) dermestids per nest and total precipitation (April–July). Beetle abundance correlated negatively with precipitation (see text). Colony-site abbreviations are as follows: PP = Pea Patch Island (Delaware Bay), SA = Sampsons Island (Cape Cod), CO = Coatue (Nantucket), SR = Sarah Island (Boston Harbor), MI = Middle Island (Rehoboth Bay), and PR = Prall’s Island (New York Harbor). 420 Northeastern Naturalist Vol. 16, No. 3 D. nidum as the sole dermestid species occupying nests of Wood Stork, Great Blue Heron, and Snail Kite (Jewell 1987, Rodgers et al. 1993, Snyder et al. 1984). Nests were apparently colonized by dermestids prior to wading-bird hatch dates unlike some nest fly species (Protocalliphora) that lay eggs only in bird nests that contain nestlings (Waldbauer 1998). No evidence was detected in our study that the number of beetles changed between egg and nestling phases of nesting, or that beetle abundance varied with nestcollection date. Dermestids are known to excavate pupal chambers in twigs, and we documented the presence of both larvae and adults in bird nests. In addition, we found no evidence that beetle abundance differed between wading-bird species. Herons typically reuse old nests (previously occupied by members of their own or other species) and steal nest material from neighbors within the colony (Davis 1993, Parsons and Master 2000, Telfair 1994). Similarly, Snyder et al. (1984) found that Snail Kite in mixedspecies colonies was more affected by dermestids than in mono-specific colonies. These results suggest that variability in dermestid abundance is a colony phenomenon rather than an event specific to a nest. Although nests were removed from nest substrates that differed markedly from each other (coniferous trees, deciduous trees, reeds), we detected no differences in beetle abundance based on nest substrate. Rodgers et al. (1993) also found no correlation between dermestid effects on Wood Stork and species of nest tree. Snyder et al. (1984) suggested that nest reuse contributed to the effects of dermestids on Great Blue Heron, but we found no consistent relationship between nest reuse and dermestid abundance. Nesting season, bird species, nest substrate, and nest reuse did not explain variability in beetle numbers; however, results from this long-term study showed that dermestid abundance was subject to high annual variability. At most colony-sites, median beetle numbers varied by an order of magnitude between years. Over the entire study area (>500 km of coast), beetle abundance was more similar within years than within colony sites. Variability in beetle abundance was partially explained by nest size and location. In addition, we speculate that there are some shifting year-to-year conditions related to beetle abundance; variation in precipitation plays a part, but doesn’t completely explain dermestid patterns. The impact of beetles on heron nestlings in our study is quantified elsewhere (Parsons et al., in press). Several studies have documented the presence of abdominal lesions on nestlings in whose nests dermestids resided (Jewell 1987, Rodgers et al. 1993, Snyder et al. 1984). In addition, the ability of Dermestes sp. to cause wounds in poultry has been documented by several researchers (Armitage 1986, Jefferies 1979, Samish et al. 1992). Although studies on wading birds did not quantify beetle abundance or reproductive endpoints associated with beetles or lesions, all authors identified the need for further study and documentation of ectoparasitism to assess effect (Jewell 1987, Rodgers et al. 1993, Snyder et al. 1984). The present study 2009 K.C. Parsons, J.E. Yacabucci, S.R. Schmidt, and N.A. Hurwitz 421 documents the importance of dermestid beetles—potential ectoparasites of birds—in wading-bird nests. Acknowledgments Financial support of this work was gratefully received from: Geraldine R. Dodge Foundation, Dolphin Trust, Island Foundation, National Fish and Wildlife Foundation, New York City Audubon Society, Sweet Water Trust, Delaware Department of Natural Resources, The William Penn Foundation, and Manomet members. William Day and Marty Averill provided helpful insights concerning dermestid ecology. We thank Bryan Wright, Amanda McColpin, Kathleen Vance, Peter Whitlock, Dale Troxel, Cris Winters, Diana Yates, Sarah Stai, Phil Magasich, and Tony Chute for technical assistance. Reviewers Jim Rodgers and Dave Duffy provided helpful comments that improved the manuscript. Literature Cited Armitage, D.M. 1986. Population changes of four species of insects (Col.& Dipt.) in three deep-pit poultry houses. Entomologists Monthly Magazine 122:75–77 Brown, C.R., and M.B. Brown. 1986. Ectoparasitism as a cost of coloniality in Cliff Swallows (Hirundo pyrrhonota). Ecology 67:1206–1218. 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Advantages and disadvantages of Bank Swallow (Riparia riparia) coloniality. Ecological Monographs 46:33–58. Jefferies, M.G. 1979. The occurrence of Dermestes species (Coleoptera: Dermestidae) in “deep pit” poultry houses in Britain. Entomologist’s Gazette 30:207–212. Jewell, S.D. 1987. Larval dermestid infestation of nestling Wood Storks (Mycteria Americana) in Georgia. Oriole 52:11–13. King, K. A., D.R. Blankinship, and R.T. Paul. 1977. Ticks as a factor in the 1975 failure of Texas Brown Pelicans. Wilson Bulletin 89:157–158. Parsons, K.C., and T.L. Master. 2000. Snowy Egret (Egretta thula). In A. Poole and F. Gill (Eds.). The Birds of North America, No. 489. The Birds of North America, Inc., Philadelphia, PA. Parsons, K.C., A.C. Matz, M.J. Hooper, and M.A. Pokras. 2000. Monitoring wadingbird exposure to agricultural chemicals using serum cholinesterase activity. Environmental Toxicology and Chemistry 19:1317–1323. 422 Northeastern Naturalist Vol. 16, No. 3 Parsons, K.C., S.R. 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