Survival and Cause-Specific Mortality of Wild Turkey Hens in Central Mississippi

Survival and Cause-Specific Mortality of Wild Turkey Hens in Central Mississippi Author(s): Darren A. Miller, Loren W. Burger, Bruce D. Leopold and George A. Hurst Source: The Journal of Wildlife Management , Jan., 1998 , Vol. 62, No. 1 (Jan., 1998), pp. 306-313 Published by: Wiley on behalf of the Wildlife Society Stable URL: https://www.jstor.org/stable/3802293 JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at https://about.jstor.org/terms Wiley and Wildlife Society are collaborating with JSTOR to digitize, preserve and extend access to The Journal of Wildlife Management This content downloaded from � � � � � � � � � � � � � 128.227.251.1 on Thu, 12 Sep 2024 15:16:31 UTC�� All use subject to https://about.jstor.org/terms SURVIVAL AND CAUSE-SPECIFIC MORTALITY OF WILD TURKEY HENS IN CENTRAL MISSISSIPPI DARREN A. MILLER,' 2 Department of Wildlife and Fisheries, Box 9690, Mississippi State, MS 39762, USA LOREN W. BURGER, Department of Wildlife and Fisheries, Box 9690, Mississippi State, MS 39762, USA BRUCE D. LEOPOLD, Department of Wildlife and Fisheries, Box 9690, Mississippi State, MS 39762, USA GEORGE A. HURST, Department of Wildlife and Fisheries, Box 9690, Mississippi State, MS 39762, USA Abstract: Most studies of hen survival of eastern wild turkey (Meleagris gallopavo silvestris) have short duration (<10 yr), and none have distinguished reproductively active (RA) from nonreproductive (NRA) hens. We examined seasonal and annual survival of radiotagged wild turkey hens and comp and NRA hens during 1984-94 in central Mississippi. Annual survival (0.224-0.770) of adult hens among years (P = 0.013), as did survival rates for all adult hens during breeding and nonbreeding int = 0.013). Survival rates of nesting and nonnesting hens did not differ during years with low, medium survival (P > 0.05). During years of high survival, survival rates of NRA and RA hens did not differ (P Preincubation and fall-winter interval survival rates did not differ within years (P > 0.05). Predation primary mortality factor, whereas illegal kill was low. Nesting hens experienced higher predation th hens during years of low (P = 0.009) and medium survival (P < 0.021). Survival cost of reproduction a with nesting was low but unknown for brood-rearing hens. JOURNAL OF WILDLIFE MANAGEMENT 62(1):306-313 Key words: Meleagris gallopavo, Mississippi, mortality rates, predation, reproductive cost, survival, w key. Low survival of hens and poults may limit productivity of some turkey populations (Miller and Leopold 1992, Palmer et al. 1993b, Peoples et al. 1995). To manage wild turkey populations more effectively, relations among patterns and sources of mortality and recruitment need to be better understood, especially given national pat- terns of increasing carnivore populations and declining recruitment of galliformes (Vangilder and Hamilton 1992, Hurst et al. 1996, Leopold et al. 1996). Although several researchers have reported survival rates for wild turkey hens during repro- ductive seasons (e.g., Palmer et al. 1993a, Rob- erts et al. 1995, Vangilder and Kurzejeski 1995, Wright et al. 1996), none have quantified cost of reproduction by comparing survival rates for RA versus NRA hens. Failure to recognize pos- sible differences in survival rates between RA and NRA hens violates a basic assumption of survival analyses: that individuals within groups are drawn from the same distribution (Heisey and Fuller 1985a, Pollock et al. 1989). Our objectives were (1) estimate annual sur- vival rates; (2) estimate survival rates during breeding and nonbreeding intervals, and nest- ing intervals within breeding intervals; (3) esti- mate survival of RA and NRA hens during breeding intervals; and (4) document cause-spe- cific mortality within a central Mississippi wild turkey population during 1984-94. STUDY AREA We conducted the study on the 14,410-ha Tallahala Wildlife Management Area (TWMA) located within the Bienville National Forest in parts of Scott, Newton, Jasper, and Smith coun- ties, Mississippi. Most (95%) of TWMA was for- ested, with 30% in mature bottomland hard- wood forests, 37% in mature pine (Pinus spp.) forests, 17% in mixed pine-hardwood forests (30-70% pine), and 11% in 1-14-year-old lob- lolly pine (P taeda) plantations. Topography was gently to moderately rolling, with 0-16% slope. Climatic conditions were mild; mean annual temperature was 180C, and mean annual pre- cipitation was 144 cm. Fall hunting of hen wild turkeys was not legal during this study. METHODS We captured wild turkey hens by cannon net (Bailey 1976) or with alpha-chloralose (Williams et al. 1966) from 7 January to 4 March and from 1 July to 25 August, 1984-94. For both capture 1 E-mail: millerd4@wdni.com 2 Present address: Weyerhaeuser Southern Forest Research, Box 2288, Columbus, MS 39704, USA. 306 This content downloaded from � � � � � � � � � � � � � 128.227.251.1 on Thu, 12 Sep 2024 15:16:31 UTC�� All use subject to https://about.jstor.org/terms J. Wildl. Manage. 62(1):1998 HEN WILD TURKEY SURVIVAL * Miller et al. 307 procedures, we used cracked corn for bait. Hens were classified as adults or subadults (Wil- liams and Austin 1988) and marked with 2 pa- tagial wing tags (Knowlton et al. 1964) and 2 metal, triple-lock leg bands. We fitted hens with 108-g motion- or mortality-sensitive backpack radiotransmitters (Wildlife Materials, Carbon- dale, Illinois, USA) and released them at cap- ture sites. We released cannon-netted turkeys within 10-45 min of capture. We transported tranquilized hens to TWMA headquarters for marking, removal of drugged corn, and recov- ery; they were released the next day. We oper- ated under Mississippi State University IACUC Protocol 93-030. Beginning on 14 March of each year, we used triangulation to locate radiomarked hens -1 time/day. Hens detected in the same location for 2 consecutive days during the nesting peri- od, or hens with a transmitter emitting a mor- tality signal, were considered incubating, and date of initiation of incubation was recorded. During other seasons (after nesting to 13 Mar of the next year), we located hens 23 times/ week. We conducted flush counts and counts of lost poults to determine brood status of most broods at 2 weeks, 4 weeks, and during early autumn (Kimmel 1983). Additionally, we re- corded ancillary observations of radiotagged hens with broods. We classified dead hens as killed by raccoon (Procyon lotor), coyote (Canis latrans), bobcat (Felis rufus), great horned owl (Bubo virgini- anus), poaching, disease (avian pox), accident (vehicle collision), or 2 unknown categories (un- known, unknown predation). We classified hen mortalities as unknown if conflicting sign was present at the kill site (e. g., carcass cached by bobcat, but coyote tracks or scat present), or an exact determination could not be made. We es- timated cause-specific mortality, predation, il- legal kill, and unknown. We entered all captured hens into the surviv- al model 7 days postcapture (Vangilder and Kurzejeski 1995). Hens released with obvious signs of injury or dying in <7 days were consid- ered trap-related mortalities and were excluded from analyses. We censored hens with radio- transmitter failures on the last day of observa- tion (Vangilder and Sheriff 1990). Hens recap- tured before radiotransmitter failure were cen- sored the day before capture and reintroduced into the model as a new observation 7 days post- recapture. Exact dates of mortalities were not always known because relocation intervals varied from daily to 3 times/week. Any hen not immediately found after death was classified as unknown, and the midpoint between the last known te- lemetry location and detection of mortality was used as the death date. Consequently, potential error for any mortality event averaged 1.5 days. Although the Heisey and Fuller (1985a) ap- proach assumes constant relocation, little bias is introduced into survival estimates using reloca- tion intervals as long as 10 days (Johnson 1979, Heisey and Fuller 1985a). Because there was no reason to suspect that relocation frequency was related to dead-alive status, and because we used the midpoint of the relocation interval to assign day of death, biases associated with in- consistent relocations were negligible. We used the Heisey-Fuller method to cal- culate survival and cause-specific mortality rates (Heisey and Fuller 1985a). Intervals without mortalities were likely reflective of low sample sizes and had no variance associated with a sur- vival estimate of 1.00 (Dugger et al. 1994). Therefore, we estimated a survival rate and variance directly from the binomial distribution (Steel and Torrie 1980, Dugger et al. 1994). We divided each year into biological intervals (Table 1). The start of the fall-winter interval coincided with the beginning of fall-winter pat- terns of habitat use (i.e., use of hard mast; Palmer 1990). The extra day during leap years (1984, 1988, 1992) was included during the fall- winter interval, although the interval was de- fined as 150 days (2 Oct-28 Feb) to maintain constant interval length. The start of the prein- cubation interval approximated beginning of break-up of winter flocks (1 Mar). The nesting interval began on 1 April be- cause this was the earliest date hens were ob- served to begin continuous incubation behavior. Hens that incubated past 29 days (n = 8) had all incubation radiodays classified as nesting, but survival rates were calculated with a 29-day in- terval length. We assumed nesting and renest- ing attempts had similar survival functions, and thus pooled attempts within the nesting interval for analyses. For hens with failed nests and no renesting attempts, we included postincubation radiodays as nonnesting (i.e., NRA) until 29 days after initiation of incubation. For unsuc- cessful hens that renested, we classified radio- days between the end of the first nest attempt This content downloaded from � � � � � � � � � � � � � 128.227.251.1 on Thu, 12 Sep 2024 15:16:31 UTC�� All use subject to https://about.jstor.org/terms 308 HEN WILD TURKEY SURVIVAL * Miller et al. J. Wildl. Manage. 62(1):1998 Table 1. Interval types, hen classes, and interval lengths for survival analyses, Tallahala Wildlife Management Area, Mississi 1984-94. Interval Hen class Interval length Annual All 1 Jan-31 Dec Breeding All 1 Apr-1 Oct Nesting Reproductive Beginning-end of incubation Nonreproductive 1 Apr-29 Apr Early brood Reproductive 14 days posthatch Nonreproductive 30 Apr-13 May Late brood Reproductive End of early brood period-1 Oct Nonreproductive 14 May-1 Oct Nonbreeding Reproductive 2 Oct-begin incubation Nonreproductive 2 Oct-31 Mar Fall-winter All 2 Oct-28/29 Feb Preincubation Reproductive 1 Mar-begin incubation Nonreproductive 1 Mar-31 Mar and beginning of the renest attempt as non- nesting. Turkey mortality is highest during the first 2- 3 weeks of life before poults begin roosting off the ground (Barwick et al. 1970, Williams et al. 1973, Glidden and Austin 1975, Peoples et al. 1995). We assumed brooding hens also were more vulnerable to predation during this time and subdivided brood intervals as early and late to reflect these mortality patterns (Table 1). The late brood interval ended when hens began to display fall-winter patterns of habitat use. For hens that lost broods during both early and late brood-rearing periods, we included radiodays until the end of the interval as NRA. Hens whose brood status became unknown were cen- sored on the last day of known brood presence and reentered at the beginning of the fall-win- ter interval. We developed reduced models to test for survival heterogeneity among years, intervals, and age. The full model consisted of 11 years (1984-94), 2 age classes (adult, subadult), and 2 intervals (breeding, nonbreeding). To ex- amine differences in survival rates, we created a reduced model by collapsing the category of interest into a single class while maintaining the full model structure for the other cate- gories. After we examined initial estimates of breeding and nonbreeding survival rates, we classified annual breeding interval rates as high (>0.80), medium-high (0.65-0.79), me- dium (0.45-0.64), or low (<0.45). Similarly, we classified annual nonbreeding intervals as high (>0.90), medium (0.40-0.89), or low (<0.40). We then tested the hypothesis that the reduced model did not differ from the original (11 yr) full model. We made statistical comparisons between full and reduced models via the absolute val- ue of the difference between the 2x log-like- lihood estimators for the full and reduced models (Heisey and Fuller 1985b, Vangilder and Kurzejeski 1995). This statistic approxi- mates a Chi-square goodness-of-fit statistic where degrees of freedom is the difference between full model degrees of freedom and reduced model degrees of freedom. All tests were performed at a = 0.05. In the interest of parsimony, we used reduced models when goodness-of-fit was similar to full models and were biologically reasonable (Heisey and Ful- ler 1985a). We tested for difference in surviv- al rates and cause-specific mortality using a Bonferroni Z-statistic (Heisey and Fuller 1985b). Interval rate was used when interval length was the same for compared survival rates. We compared daily survival rates when interval lengths differed or when we estimat- ed an adjusted daily survival rate. We com- pared only those mortality rates within inter- val pairs that had at least 1 mortality event from the category of interest. We tested the hypotheses that reproductive status did not affect hen survival during nesting or during the entire breeding interval. Because there were too few brood hens, we did not make a separate survival estimate during the brood-rearing interval. We estimated survival rates for hens within the preincubation interval, the fall-winter interval, and the overall non- breeding interval, and tested the hypothesis that This content downloaded from � � � � � � � � � � � � � 128.227.251.1 on Thu, 12 Sep 2024 15:16:31 UTC�� All use subject to https://about.jstor.org/terms J. Wildl. Manage. 62(1):1998 HEN WILD TURKEY SURVIVAL * Miller et al. 309 survival did not differ between the fall-winter and preincubation intervals. RESULTS We used 237 adult hens (200 individuals) with 50,388 radiodays and 57 subadult hens (54 individuals) with 12,493 radiodays. Of these hens, 109 had radiofailures, 23 were censored the day before a recapture, 2 were censored at the end of the early brood season because of unknown brood status, and 110 died. We attrib- uted 51 (46.4%) mortalities to predators (9 great-horned owl, 6 bobcat, 5 coyote, 4 raccoon, 5 unknown mammal, 22 unknown predator), 11 (10.0%) to poachers, 2 (1.8%) to vehicle colli- sions, 3 (2.7%) to avian pox, and 43 (39.1%) to unknown causes. Survival rates differed annually (X211 = 24, P = 0.013) and between adult and subadult hens (X220 = 63, P < 0.001). Because we observed an age effect, subadult hens on TWMA contrib- uted little to recruitment (Palmer et al. 1993b, Miller 1997), and a low number of subadult hens (n = 54) were available, we used only adult hens for subsequent analyses. Annual sur- vival rates for adult hens averaged 0.508 and varied from 0.224 to 0.770 (Table 2). Survival rates for breeding and nonbreeding intervals also differed (X211 = 24, P = 0.013); rates varied from 0.344 to 0.899 during breeding intervals and 0.291 to 1.000 during nonbreeding intervals (Table 2). With the exception of the 0.291 sur- vival rate for 1987, survival rates during the nonbreeding interval were 20.778. The reduced model with survival during breeding intervals grouped into low (1986, 1989, 1992, 1993), medium (1988, 1990, 1994), medium-high (1991), and high (1984, 1985, 1987) years did not differ from the full model (X27 = 4.0, P = 0.779). Likewise, the reduced model for the nonbreeding interval was not dif- ferent than the full model (4s = 6.0, P = 0.647), with years grouped as high (1990-91), medium (1984-86, 1988-89, 1992-94), and low (1987). The model with which we estimated survival rates for RA and NRA hens within the breeding and nesting intervals had 1 age class (adults) and 4 year groupings (high, medium- high, medium, low survival). For the nonbreed- ing interval, the model had 1 age class (adults) and 3 year groupings (high, medium, low sur- vival). Because sample sizes were low, we did not estimate survival rates for the breeding in- terval during medium-high survival years and Table 2. Interval survival rate estimates, variances, and sam- ple sizes for annual, breeding (1 Apr-1 Oct), and nonbreeding (2 Oct-31 Mar) intervals for radiotagged wild turkey hens, Tal- lahala Wildlife Management Area, Mississippi, 1984-94. Survival Sample Year Interval estimate Variance size 1984 Annual 0.770 0.0125 19 (13)a Breeding 0.899 0.0082 19 (24) Nonbreeding 0.863 0.0076 19 (29) 1985 Annual 0.755 0.0091 27 (26) Breeding 0.883 0.0057 27 (16) Nonbreeding 0.846 0.0063 28 (29) 1986 Annual 0.382 0.0113 28 (23) Breeding 0.432 0.0129 28 (10) Nonbreeding 0.858 0.00812 30 (6) 1987 Annual 0.224 0.0097 22 (5) Breeding 0.878 0.0116 22 (24) Nonbreeding 0.291 0.0109 23 (40) 1988 Annual 0.551 0.0082 43 (41) Breeding 0.608 0.0089 43 (36) Nonbreeding 0.862 0.0039 45 (41) 1989 Annual 0.343 0.0063 40 (36) Breeding 0.348 0.0075 40 (18) Nonbreeding 0.874 0.0044 46 (12) 1990 Annual 0.634 0.0189 22 (10) Breeding 0.581 0.0189 22 (18) Nonbreeding 0.999 0.0063 23 (10) 1991 Annual 0.772 0.0205 15 (6) Breeding 0.755 0.0204 15 (13) Nonbreeding 0.999 0.0058 16 (10) 1992 Annual 0.307 0.0165 19 (6) Breeding 0.344 0.0225 19 (13) Nonbreeding 0.778 0.0175 18 (10) 1993 Annual 0.378 0.0228 13 (7) Breeding 0.356 0.0269 13 (11) Nonbreeding 0.876 0.0122 14 (14) 1994 Annual 0.474 0.0212 13 (10) Breeding 0.559 0.0249 13 (7) Nonbreeding 0.806 0.0140 16 (14) a First number is beginning interval sample size; parenthetical value is end of interval sample size. the nonbreeding interval during low survival years. Within the nesting interval, we observed no differences between survival of nesting and nonnesting hens during low (Z = 0.05, P > 0.5), medium (Z = 0.82, P = 0.21), or high (Z = 0.00, P > 0.5) survival years (Table 3). During low survival years, 5 hens hatched broods; 3 of these hens were killed by predators. During medium survival years, 6 hens hatched broods; 1 of these hens was depredated. Low sample sizes prevented our estimation of breeding in- terval survival rates for RA hens during low and medium years. Survival rates for NRA hens dur- ing the breeding interval were 0.470 during low survival years and 0.680 during medium suvival years. During high survival years, RA and NRA survival rates did not differ (Z = 0.01, P > 0.5). This content downloaded from � � � � � � � � � � � � � 128.227.251.1 on Thu, 12 Sep 2024 15:16:31 UTC�� All use subject to https://about.jstor.org/terms 310 HEN WILD TURKEY SURVIVAL * Miller et al. J. Wildl. Manage. 62(1):1998 Table 3. Interval survival estimates, variances, and sample sizes within nesting intervals (1-29 Apr) and breeding intervals Apr-1 Oct) within low (<0.45), medium (0.45-0.64), and high (>0.80) survival years for reproductively active and nonreproductive adult wild turkey hens, Tallahala Wildlife Management Area, Mississippi, 1984-94. Nesting Breeding Parameter Low Medium High Low Medium High Reproductive hens Survival estimate 0.728 0.753 0.999a NEb NE 0.999a Variance 0.047 0.0074 0.0680 0.026 Sample size 53 (41)c 39 (30) 37 (37) 37 (8) Radiodays 1,028 629 693 1,797 Nonreproductive hens Survival estimate 0.740 0.842 0.999d 0.471 0.678 0.999C Variance 0.0041 0.0034 0.0000031 0.00408 0.00523 0.00000019 Sample size 33 (17) 23 (15) 9 (4) 33 (71) 23 (72) 9 (63) Radiodays 1,178 1,026 572 6.450 6,116 4,588 a Daily survival rate estimated from binomial distribution. b Not estimated because of low sample size during brood rearing. c First number is beginning interval sample size; parenthetical value is end of interval d Daily survival rate as estimated from MICROMORT (Heisey and Fuller 1985b). Within the nonbreeding interval, we detected no differences between preincubation and fall- winter intervals in either high (Z = 0.01, P > 0.5) or medium (Z = 0.66, P = 0.26) survival years (Table 4). Patterns of mortality varied among intervals and between reproductive statuses (Table 5). Predation was the primary cause of mortality within all intervals. Predation rates varied be- tween nesting hens within low and medium sur- vival years (0.243) and preincubation and nest- ing (RA, NRA) intervals within high survival years (0.0). Illegal kill of RA hens did not occur during either the nesting or the breeding inter- val. Poaching was most prevalent for NRA hens (0.040) during the low survival, nonbreeding in- terval. Mortality from unknown causes was highest during the low survival, nonbreeding in- terval for NRA hens (0.282). Nesting hens had higher predation rates than nonnesting hens within low (Z = 2.37, P = 0.009) and medium (Z = 2.2.04, P = 0.021) survival years (Table 5). Within low survival years, nonnesters were more likely to succumb to unknown causes than nesters (Z = 2.49, P = 0.006). Within medium survival years of non- breeding intervals, fall-winter and preincuba- tion did not differ with respect to predation (Z = 1.12, P = 0.131), poaching (Z = 1.13, P = 0.129), or unknown causes (Z = 1.31, P = 0.095). DISCUSSION Our mean annual survival rate of hens was similar to rates reported for established turkey populations (Little et al. 1990, Vangilder 1992, Roberts et al. 1995, Wright et al. 1996) but low- er than other established populations (Van der Table 4. Interval survival estimates, variances, and sample sizes within preincubation (1-31 Mar) and fall-winter interval (2 Oct-28 or 29 Feb) within high (>0.90) and medium (0.40-0.89) survival years for adult wild turkey hens, Tallahala Wildlife Management Area, Mississippi, 1984-94. Parameter High Medium Preincubation interval Survival estimate 0.999a 0.963 Variance 0.0140 0.000146 Sample size 25 (21)b 25 (16) Radiodays 1,058 7,417 Fall-winter interval Survival estimate 0.999C 0.903 Variance 0.00000011 0.000841 Sample size 176 (156) 196 (163) Radiodays 2,945 14,786 a Daily survival rate estimated from binomial distr b First number is beginning interval sample size; p c Daily survival rate as estimated from MICROM This content downloaded from � � � � � � � � � � � � � 128.227.251.1 on Thu, 12 Sep 2024 15:16:31 UTC�� All use subject to https://about.jstor.org/terms J. Wildl. Manage. 62(1):1998 HEN WILD TURKEY SURVIVAL * Miller et al. 311 Table 5. Cause-specific mortality estimate and associated variances within nesting (1-29 Apr) and breeding intervals (1 Apr 1 Oct) within low (<0.45), medium (0.45-0.64), and high (>0.80) survival years, between nesting (Nests) and nonnesting wild turkey hens (Nonnest), and between reproductively active (RA) and nonreproductively active wild turkey hens (NRA), and al wild turkey hens within preincubation (PI; 1-31 Mar) and fall-winter (FW; 2 Oct-28 or 29 Feb) intervals within medium (0.40 0.89) and high (>0.90) survival years, Tallahala Wildlife Management Area, Mississippi, 1994-95. Mortality agent Predation Poaching Unknown Mortality Mortality Mortality Interval estimate Variance estimate Variance estimate Variance Low Nest 0.243 0.0045 0.000 0.000 0.024 0.000579 Nonnest 0.064 0.0013 0.021 0.00049 0.171 0.00303 RA NEa NE NE NRA 0.201 0.0040 0.040 0.00078 0.282 0.00402 Medium Nest 0.243 0.0074 0.000 0.000 0.000 0.000 Nonnest 0.052 0.0013 0.026 0.00067 0.078 0.00402 RA NE NE NE NRA 0.146 0.0030 0.048 0.0011 0.122 0.00261 High Nest 0.000 0.000 0.000 0.000 0.000 0.000 Nonnest 0.000 0.000 0.000 0.000 0.049 0.00233 RA 0.000 0.000 0.000 0.000 0.000 0.000 NRA 0.074 0.0025 0.000 0.000 0.074 0.00254 Medium FW 0.028 0.00027 0.019 0.00018 0.048 0.000443 PI 0.012 0.000050 <0.010 0.000017 0.020 0.0000825 High FW 0.049 0.0023 0.000 0.000 0.000 0.00 PI 0.000 0.000 0.000 0.000 0.000 0.00 Not estimatable due to low sample sizes during b Haegan et al. 1988, Palmer et al sistent with other studies, surviv during the breeding interval ( 1993a, Roberts et al. 1995; Vangil zejeski 1995, Wright et al. 1996). difference between subadult and adult hens was consistent with some studies (Roberts et al. 1995, Vangilder and Kurzejeski 1995) but dif- fered from others (Van der Haegen et al. 1988, Little et al. 1990). We had a high incidence of unknown causes of death (0.374) because of our conservative es- timate of cause of death. We established only 3 mortality categories (known predation, known poaching, unknown); hence, we were less likely to misclassify a mortality event. These factors contributed to the large number of unknown deaths and made our estimates of predation and poaching conservative. During nesting, survival rates were similar for both classes of hens, although mortality causes differed. For nesting hens within both low and medium survival years, predation was the pri- mary cause of mortality and was significantly higher than predation on nonnesting hens. Con- versely, nonnesting hens experienced low (<0.10) predation rates but higher deaths from unknown causes during low and medium sur- vival intervals. Illegal kill was not an important factor af- fecting this wild turkey population. Losses to poaching during an interval never exceeded 0.04. Illegal kill was an important mortality fac- tor in Missouri during 1981 (0.29), 1982 (0.69), and 1984 (0.36; Kimmel and Kurzejeski 1985), varied between 0.028-0.374 in Missouri during 1980-89 (Vangilder and Kurzejeski 1995), and accounted for 38.7% of hen losses in northern Missouri (Kurzejeski et al. 1987). High rates also were reported for Kentucky (approx 0.20; Wright and Speake 1975) and Alabama (0.40- 0.50; Fleming and Speake 1976). However, Palmer et al. (1993a) did not find illegal killing of hens important (0.03) in eastcentral Missis- sippi. Wright et al. (1996) determined illegal kill in Wisconsin occurred only during spring and was only 0.023. Vangilder and Kurzejeski (1995) detected no relation between incubation status and illegal kill. On TWMA, only nonincubating hens were poached during the breeding inter- This content downloaded from � � � � � � � � � � � � � 128.227.251.1 on Thu, 12 Sep 2024 15:16:31 UTC�� All use subject to https://about.jstor.org/terms 312 HEN WILD TURKEY SURVIVAL * Miller et al. J. Wildl. Manage. 62(1):1998 val, which suggests that hen incubation status may be an important determinant of suscepti- bility to poaching on our study area. Environmental conditions may have affected survival of hens. Northern turkey populations may experience higher mortality during adverse winter conditions (Roberts et al. 1995, Wright et al. 1996). On TWMA, the worst drought in Mississippi history occurred during July 1987- June 1988 (Seiss 1989). Additionally, complete failures of hard mast occurred during 1984-85 and 1987-88 (Seiss 1989, Hurst 1992:80). Dur- ing the 1987 nonbreeding interval, which oc- curred during the drought, hen survival was only 0.291, or 0.487 lower than the next lowest interval. Turkeys during this time may have suf- fered synergistic effects of poor winter and summer environmental conditions, thus placing them in poorer physiological condition and sub- sequently increasing probability of mortality. Cost of reproduction for nesting hens, as measured by survival probability, was minimal because RA hens and NRA hens had similar survival rates during nesting. Nesting hens were more susceptible to losses from predation, while nonnesting hens were more likely to be killed illegally. We were unable to quantify cost of re- production associated with brood rearing, but this cost is likely high. Of 11 broods followed during low and medium survival years, 6 brood hens were depredated. This predation rate compares to a relatively high survival rate and low predation rate of NRA during this time. During high predation years, RA and NRA hens survived similarly, which indicated cost of re- production may be variable among years. Al- though these rates are not directly comparable, they do provide some indication as to potential costs of reproduction during brood rearing. MANAGEMENT IMPLICATIONS Consistent with other research, our data in- dicate predation was a primary mortality agent for hen wild turkeys, especially for reproduc- tively active hens. Provision of adequate nesting and brood-rearing cover may be especially im- portant to decrease predation rates on repro- ductive hens. Our data indicate hens were most vulnerable to illegal kill when not incubating nests. Finally, it is important to recognize pos- sible heterogenous survival rates between re- productive classes so that reliable information can be obtained for survival rates. Partitioning variance by reproductive status would be an as- set for investigations into wild turkey population dynamics. ACKNOWLEDGMENTS We thank 2 anonymous reviewers for helpful comments; M. M. Miller and H. M. Miller pro- vided additional support. We acknowledge the tireless efforts of "Tallahala" graduate students and technicians for data collection. Funding was provided by the Mississippi Department of Wildlife, Fisheries and Parks through Federal Aid in Wildlife Restoration Project 39-43, The National Wild Turkey Federation (NWTF), Mississippi Chapter of NWTF, U.S. Forest Ser- vice, and the Department of Wildlife and Fish- eries, Mississippi State University. This manu- script is a contribution of the Mississippi Co- operative Wild Turkey Research Project and the Mississippi Forest and Wildlife Research Cen- ter. Additional support was provided by Wey- erhauser Company, Southern Forestry Re- search. LITERATURE CITED BAILEY, R. W. 1976. Live-trapping wild turkeys in North Carolina. North Carolina Wildlife Re- sources Commission, Raleigh, North Carolina, USA. BARWICK, L. H., D. H. AUSTIN, AND L. E. WILLIAMS, JR. 1970. Roosting of young turkey broods dur- ing summer in Florida. 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