Peter G. May

Secondary succession and breeding bird community structure: Patterns of resource utilization

SummaryStructure of breeding bird communities was compared among four habitat types representative of stages present in most old-field successions in the eastern deciduous forest formation of North America. The successional catagories, defined by vegetational structure, were designated herbaceous (type A habitats) herb, shrub and sapling (type B), young forest (type C), and older forest (type D). Density of breeding birds was lowest in A habitats, rose sharply in B habitats and reached a maximum in D habitats. Species richness and number of feeding guild showed similar patterns. Mean number of species per guilds was highest in D habitats. Generalist feeding guilds were predominant in type A and B habitats, primarily due to the importance of the graminivore-insectivore guild. Specialist guilds increased in importance with succession due to addition of several insectivorous guilds in later successional stages. Patterns of occurrence of individual feeding guilds are analyzed and discussed with respect to changes in vegetational structure. Variance in community structure was generally highest in A habitats and lowest in D habitats; this is discussed in relation to the evolution of “saturated”, coadapted communities.

REPRODUCTION IN THE RATTLESNAKE, SISTRURUS MILIARIUS BARBOURI, IN CENTRAL FLORIDA

-We studied reproduction in female pigmy rattlesnakes in a subtropical area. Twenty-six females were either captured gravid and held until parturition or found in the field with their litters. Over 92% of the snakes gave birth in August. Individuals with large clutch masses gave birth earlier in the season than individuals with small clutch masses. Mean clutch size was 5.88 (range 2-11). Litter size and clutch mass were significantly correlated with female SVL. There was significant variation in offspring size among females, but this variation was not a result of larger females having larger young, or the young being smaller in larger litters. Of 19 females whose reproductive condition was determined in the summers of both 1992 and 1993, 32% were not gravid in either year, 42% were gravid in one of the two years, and 26% were gravid in both years. We hypothesize that annual reproduction in some females is a result of the year-round activity of S. miliarius in central Florida. Journal of Herpetology, Vol. 29, No. 1, p . 21-27, 1995 Copyright 1995 Society for the Study of Amphibians and Reptiles Reproduction in the Rattlesnake, Sistrurus miliarius barbouri, in Viperids typically exhibit a suite of life history characteristics, including slow growth, which results in delayed maturation and low frequency of reproduction (LFR) by adult females (Dunham and Miles, 1985). In many viperids most adult females reproduce every other year (reviewed by Seigel and Ford, 1987; Dunham et al., 1988) and in some species females reproduce only every third or fourth year (Macartney and Gregory, 1988; Brown, 1991; Martin, 1993). It is not clear why viperids lack t e resources for frequent reproduction (Seigel and Ford, 1987). Shine (1991) suggests that sitand-wait predators, including most viperids, will tend to have low foraging success compared to snakes that actively search for prey. Some costs of reproduction resulting from viviparity may be independent of fecundity. For example, gravid females may need to move to basking sites with low prey availability to accelerate development of young. These fecundity-independent costs of reproduction may re21 This content downloaded from 207.46.13.169 on Sat, 01 Oct 2016 05:31:40 UTC All use subject to http://about.jstor.org/terms T. M. FARRELL ET AL. sult in LFR (Bull and Shine, 1979). Shine (1980) also suggested that sit-and-wait predators are less likely to be detected by their own predators and therefore have the high survivorship rates that are needed to make delayed maturity and infrequent reproduction a potentially successful life history. Another factor that may result in LFR is short activity periods imposed by climatic factors. Thoroughly studied viperid populations have been most frequently found in high latitude or high altitude sites (e.g., Macartney and Gregory, 1988; King and Duvall, 1990; Brown, 1991; Madsen and Shine, 1993; Martin, 1993), where cold weather results in prolonged periods of hibernation. Martin (1993) reviewed evidence that indicates the length of the yearly activity period in Crotalus horridus influences both the age of first reproduction and reproductive frequency. Similarly, Larsen et al. (1993) found that Thamnophis sirtalis, an active foraging colubrid, exhibited LFR near its northern distributional limit. If viviparity and foraging mode are the major determinants of life history characteristics in viperids, then subtropical and tropical species should often exhibit LFR, just as in temperate species. If, however, the length of the activity season is an important factor then we expect that viperid populations in warm regions will exhibit LFR less often. Unfortunately, we know very little about reproductive frequency and other life history traits of viperids in subtropical and tropical regions. The pigmy rattlesnake has a broad range, including subtropical areas, and is fairly common in much of its range. However, few studies have addressed its life history (Ernst, 1992). In this study we present a detailed examination of reproductive parameters of Sistrurus miliarius barbouri, including (a) data from a large sample of females encompassing the full range of sizes at which these snakes reproduce, and (b) data on the frequency of reproduction in females. In central Florida, S. miliarius can be found in a variety of habitats, ranging from drier pine uplands to seasonally flooded hardwood forests. In this subtropical region rattlesnakes are active above ground throughout the year. The highest density populations (>40 rattlesnakes/ ha, unpubl. data) are found in mesic habitats located near freshwater marshes where they feed primarily on lizards (Scincella laterale, Eumeces inexpectatus, Anolis carolinensis) and frogs (Hyla spp. and Rana utricularia). MATERIALS AND METHODS Our study sites were four tracts of mesic-hydric forest dominated by live oak, sabal palmetto, red maple, and scattered slash pines. The sites were along the floodplain of the St. Johns River in Volusia County, Florida and were seprated by <4 km. We visually searched for S. m. barbouri in our study sites from 17 February 1992 to 31 August 1993. We individually marked snakes when they were first captured by scale clips (February-July 1992) or PIT-tags (after August 1992). For each snake, we measured weight using spring-loaded Pesola scales, and snoutvent length (SVL) in a squeeze box (Quinn and Jones, 1974). The reproductive condition of each snake was determined by palpation. Data were collected in the field and the snakes were rel ased at the site of capture within approximately 15 min of capture. To study reproduction more fully we held some gravid females captive until they gave birth. They were collected by visually searching the study sites in the morning or late afternoon. We placed cages in one hammock to hold gravid females until birth. The cages measured 0.6 m x 0.6 m x 0.25 m (1 x w x h) and were made of wood framing surrounded by aluminum screen (mesh size = 1 mm x 1 mm). A layer of dirt and leaf litter was placed in the cages along with a length of PVC pipe (5 cm diameter, 30 cm long) and a piece of oak or pine bark to provide shelter. The cages were exposed to direct sunlight for much of the day to allow females to bask. A palm frond was placed on each cage to provide shade. Once placed in a cage, each gravid snake was hecked daily until it gave birth. Snakes had access to water but were not fed. After parturition, the female and young were brought into the laboratory for measurement of mass and length. The data were analyzed using Systat (Wilkinson, 1988). Since many correlations were carried out in this analysis, we used a sequential Bonferroni technique (Rice, 1989) to ensure the probability of Type I error was less than 0.05 for the correlation matrix involving reproductive variables (Table 1).

AN OUTBREAK OF FUNGAL DERMATITIS AND STOMATITIS IN A FREE-RANGING POPULATION OF PIGMY RATTLESNAKES (SISTRURUS MILIARIUS BARBOURI) IN FLORIDA

Between September 1997 and March 1998, a severe skin, eye, and mouth disease was observed in a population of dusky pigmy rattlesnakes (Sistrurus miliarius barbouri), at the Lake Woodruff National Wildlife Refuge in Volusia County, Florida (USA). Three affected pigmy rattlesnakes were submitted for necropsy. All snakes had severe necrotizing and predominantly granulomatous dermatitis, stomatitis, and ophthalmitis, with involvement of the subadjacent musculature and other soft tissues. Numerous fungal hyphae were seen throughout tissue sections stained with periodic acid Schiff and Gomoris methenamine silver. Samples of lesions were cultured for bacteria and fungi. Based on hyphae and spore characteristics, four species of fungi were identified from culture: Sporothrix schenckii, Pestalotia pezizoides, Geotrichum candidum (Galactomyces geotrichum), and Paecilomyces sp. While no additional severely affected pigmy rattlesnakes were seen at the study site, a garter snake (Thamnophis sirtalis) and a ribbon snake (Thamnophis sauritis) with similar lesions were found. In 1998 and 1999, 42 pigmy rattlesnakes with multifocal minimal to moderate subcutaneous masses were seen at the study site. Masses from six of these snakes were biopsied in the field. Hyphae morphologically similar to those seen in the severe cases were observed with fungal stains. Analysis of a database representing 10,727 captures in previous years was performed after the 1998 outbreak was recognized. From this analysis we determined that 59 snakes with clinical signs similar to those seen during the 1998 outbreak were documented between 1992 and 1997. This study represents the first documented report of a mycotic disease of free-ranging snakes.

Seasonal Abundance and Activity of a Rattlesnake (Sistrurus miliarius barbouri) in Central Florida

phology. Unpubl. Ph.D. diss. Univ. of Chicago, Chicago. 1. 987. Osteology of Hypostomus plecostomus (Linnaeus) with a phylogenetic analysis of the loricariid subfamilies (Pisces: Siluroidei). Contributions in science, Natural History Museum of Los Angeles County 394:1-31. TAYLOR, W. R., AND G. C. VAN DYKE. 1984. Revised procedures for staining and clearing small fishes and other vertebrates for bone and cartilage study. Cybium 9:107-119.

PIGMY RATTLESNAKES USE FROG-DERIVED CHEMICAL CUES TO SELECT FORAGING SITES

We performed a field experiment to test the hypothesis that pigmy rattlesnakes select foraging locations based on the presence of prey odor. We established six pairs of parallel transects, each 25 m long; the experimental transect was sprayed with distilled water in which leopard frogs had been housed for 48 h, and the parallel control transect was sprayed only with distilled water. The transects were then censused for the presence of pigmy rattlesnakes at 24-h intervals for the next 96 h. More snakes were found along the experimental transects at all times, and significantly more (P = 0.019, binomial test) were found at 72 h after spraying. Our results indicate that prey odor is at least one of the factors involved in foraging site selection by these sit-and-wait predators.

Defensive Behavior of Free-Ranging Pygmy Rattlesnakes (Sistrurus miliarius)

Abstract Sistrurus miliarius frequently bites humans in the southeastern United States. We used a large population of S. miliarius in central Florida to investigate the importance of several factors on the defensive behavior of this species. Upon detection of a snake, we tapped the snout of the snake with a gloved hand. We recorded whether the snake struck or fled. Our large sample size (N = 336) allowed us to make strong conclusions regarding the defensive behavior of this rattlesnake species. Overall, only 27 snakes (8%) bit the glove indicating that this species is rather nonaggressive. Initial posture was the only factor that influenced striking behavior; uncoiled snakes struck significantly more than coiled snakes. Fleeing behavior was affected by three variables: sex; whether the snake was about to shed; and initial posture. Females fled more often than males, as did snakes about to shed. Initial posture is the only factor that affected both response variables, and uncoiled individuals were more likely to flee than coiled snakes.

Avian Reproductive Output in Early and Late Successional Habitats

Annual reproductive output (clutch size x number of broods yr-1) is investigated in breeding bird communities inhabiting four successional habitat categories to test the prediction that early successional species produce more offspring than late successional species. Early successional species are found to have a significantly higher reproductive output than late successional species due to a greater incidence of multiple-brooding. Mean clutch sizes do not differ significantly among bird species inhabiting different successional habitats.

Experimental Manipulation of Tail Color Does Not Affect Foraging Success in a Caudal Luring Rattlesnake

Abstract Snakes that exhibit caudal luring typically have a conspicuously colored tail tip. We conducted a field experiment to test the adaptive significance of tail color. A sample of 169 neonate Pigmy Rattlesnakes (Sistrurus miliarius) was treated by coloring their yellow tails with either black pigment similar to their cryptic body color or yellow ink as a procedural control. Snakes were released and recaptured over the next three months. Tail color manipulation did not significantly influence the proportion of snakes with palpable food. Also, the treatments did not affect growth in SVL or mass. These findings suggest that snakes with cryptic tails did not experience reduced prey capture. The presence of conspicuous tail coloration in this species may be explained by phylogenic inertia, selective benefits of small magnitude, or by habitat-related differences in prey composition or abundance.

Repeatability of Female Reproductive Traits in Pigmy Rattlesnakes (Sistrurus miliarius)

Abstract The consistency of a traits expression within individuals reflects both its maximal possible heritability and that traits susceptibility to the influence of temporal variation in environmental conditions. A lack of repeatability in reproductive traits may also result if there are ontogenetic changes in female reproductive effort. In a decade-long study, we collected data on the reproductive traits (including female SVL, female postpartum condition, litter size, total litter mass, mean offspring mass, and birth date) of free-ranging Pigmy Rattlesnakes in central Florida. We captured and held the study snakes in field enclosures for several weeks before parturition each year. A total of 24 females produced two or more litters during the course of the study. We determined the repeatability for each reproductive trait. Our results indicated that four of the six reproductive traits had high and statistically significant repeatability despite annual variation in environmental conditions. A lack of growth in adult Sistrurus miliarius and the ability of females to skip reproduction in some years appear to foster the high repeatability of reproductive traits. Our research and previous studies indicate that many, but not all, reproductive traits in female snakes are highly repeatable. The repeatability of a few traits, particularly post-partum female condition, is likely to depend strongly on the reproductive mode of the species.

GROWTH PATTERNS OF DUSKY PYGMY RATTLESNAKES (SISTRURUS MILIARIUS BARBOURI) FROM CENTRAL FLORIDA

Abstract:  We studied growth in snout–vent length (SVL) and body mass of Dusky Pygmy Rattlesnakes (Sistrurus miliarius barbouri) in Volusia County, Florida, with the use of mark–recapture techniques. Between February 1992 and December 2000, we PIT-tagged (Passive Integrated Transponder) 665 individuals of approximately 1 yr of age or greater that were subsequently recaptured at least once. Because snakes can be definitively aged at 1 yr, this resulted in a large sample of snakes of known age that were followed for up to 7 yr. Seventy-five of these individuals PIT tagged at 1 yr were identified from photographs of neonates born in captivity, allowing us to relate adult growth to neonate traits. Our data suggest that Pygmy Rattlesnakes in central Florida exhibit highly variable patterns of growth that are related to a mild climate that allows feeding and growth throughout the year, and to a fluctuating prey base that results in irregular growth patterns often unlike those predicted by typical growth equations such as the von Bertalanffy model. Snakes in our populations were surface-active throughout the year, and snakes with detectable prey in the gut were found in all months. Growth is most rapid in the first year, but growth rates did not differ markedly from other viperids occurring in more temperate areas. In their first year, Pygmy Rattlesnakes in Florida increased their mass over birth on average more than fourfold, and increased SVL 1.8-fold. Growth in both mass and SVL continued throughout life, with no clear indication of an asymptote in size. Multiple regressions of SVL and body mass against age showed a slight but significant effect of sex on both SVL and mass, though these differences were not apparent until snakes were approximately 4 yr. Males and females showed no difference in SVL growth rates or patterns of change in growth rate with age, but females grew faster in body mass than males. Body-mass growth rates did not decline with age in either sex. Rates of increase in SVL in the first year of life differed significantly among years, though these differences were not correlated with estimates of prey (frog) abundance. However, neither body size at birth or first-year growth rates was significantly related to size at 1 yr of age or with growth rates later in life. Inspection of individual growth records and characterization of records into categories defined here showed great variability in patterns of growth, with episodic growth occurring in most individuals, including larger adults. A year-round activity season may decouple feeding and growth in these snakes from the temporal constraints imposed on more northern snakes, resulting in greater variability in individual growth trajectories. Prolonged feeding opportunities may allow snakes with below-average feeding conditions in their first year to compensate for slower initial growth by opportunistic feeding and rapid bouts of growth at any time later in life.