Weaver Dunes, Minnesota

Transcription

1 Hatchling Orientation During Dispersal from Nests Experimental analyses of an early life stage comparing orientation and dispersal patterns of hatchlings that emerge from nests close to and far from wetlands

2 Weaver Dunes, Minnesota Blanding sturtles (Threatened) Nests far from marsh (mean = 622 m, m, n = 138) Snapping Turtles (Special Concern) Nests close to marsh (mean = 75 m, m, n = 87) Painted Turtles (Harvested) (mean = 65 m, m, n = 113)

3 Life Histories Age specific schedules of reproduction and death Longevity and long reproductive lifespan Dl Delayed sexual maturity Low annual fecundity High and unpredictable nest mortality rates in most cases. For some species: Indeterminate growth (older = larger) High average annual survival of juveniles from age 1 to first reproduction Evolutionary life history patterns are just as much a part of what organism is as are its anatomy, physiology, and morphology. George Williams

4 Why hatchling orientation is important in the context t of life-histories i Stable populations of long-lived lived organisms with low fecundity and delayed sexual maturity (i.e. turtles), require high average annual survivorships of juveniles. Average juvenile survivorships of Blanding s and Snapping turtles tl were both th>0 0.72(Congdon et al. 1993, 1994). Factors that handicap hatchlings during dispersal from nests (and cause increased mortality) will result in requiring higher survivorships at subsequent ages.

5 After emerging from nests, most hatchling freshwater turtles face a major problem - finding suitable wetlands The abilities and tactics of water finding by hatchlings co-evolved with the nesting tactics of females Therefore, patterns of co-evolution of nesting tactics and hatchling orientation and dispersal should ldbe evident among species and and families of turtles.

6 Relative constraints on terrestrial movements EB CS CP Adults Hats Adults Hats Adults Hats Predator Desiccation

7 Potential Mechanisms Random dispersal (the null hypothesis) POTENTIAL CUES FOR NON-RANDOM DISPERSAL Negative geotaxis (go down hill) Phototaxis Chemotaxis (olfaction) Humidity Auditory cues Social facilitation (scent trailing) DEVELOPED SKILLS Piloting based on landmarks Compass orientation (e.g., sun compass) True navigation (requires a map and compass)

8 Weaver Dunes Marshes 1200 h Dunes 600 h Miss Miss. River Weaver Bottoms 1500 h

9 Experimental protocols for eggs and hatchlings: ensuring hatchlings are naïve - eggs from nests or oxytocin incubated in natural protected area and removed in dark under tarp - transport to a dark room in light proof containers - after hatching (n = 2575), individuals marked by cohort # and assigned to a release bucket in the dark (red bulb)

10 Experimental release protocols (arenas ~ 90 m diameter) - Fall and Spring N E S West Newton Field (90 x 280 m)

11 Release hatchlings at center of arena in light-proof bucket with 4 release holes facing N, E, S & W (remove in 45 min.) Walk fence Record time, location, clutch i.d. of hatchlings Record time, location, clutch i.d. of hatchlings found in buckets or at the fence

12 Experimental protocols (analysis) Fence locations at 16 points (+ fractions) converted to degrees W = 12 N = 0 E = 4 Results s analyzed a and plotted S = 8 with Oriana package for circular statistics Patterns of orientation in a variety it of situations ti (natural and unnatural) were examined to infer environmental cues Blanding s turtles McCarthy WMA Snapping turtles being used by hatchlings

13 M a r s h e s 2001 Swale 2002 Flat Dunes McCarthy WMA Blanding s and Snapping turtles (2001 & 2002) Blanding s turtle Pond(175 m) N SPH Pond (280 m) McCarthy Snapping turtles 2001 N SPH (220 m) (95 m) 0 McCarthy (2002) N = 82 W WMA (265 m) (340 m) LPH (135 m) m 0 LPH (175 m) m E WATSON-WILLIAMS WILLIAMS F-TESTS: F = 4.615, p = 0.033, df = 1, 224 W WMA (265 M) LPH (135 m) m E S S

14 Non-native Pine Row Riparian Tree-line

15 WNF Blanding s, Snapping and Painted Turtles 0 EB CS CP DEG - CP

16 W Hwy 84 Naive 2001 Naive Hatchlings Blanding s turtles (Sun Compass) 2002 Naive Experienced M a r s h e s E D u n e s Experienced S M a r s h e s

17 Congdon, Pappas, Brecke. Fig. 4. Snapping turtle (time of day) - day vs. evening release AM PM

18 All hatchling release dispersal patterns (n = 31) Random 28 non-random vs. 3 random (EB s) (dispersals are species-specific) Geotaxis no evidence Horizon Painted and Snapping turtles (light-open) Horizon (dark -closed) Blanding s turtles Olfaction no evidence Social facilitation (scent trailing) no evidence Humidity no evidence Learning (encoding) Blanding s (others not tested)

19 After nest dispersal Recruitment habitat Shallow water with minimal depth and current with vegetation structure for protection from predators, abiotic extremes (first overwintering) i and source of food Acquisition and management of species specific or common aquatic recruitment hbi habitat

20 marshes reservoir aging marshes

21 Habitat Alteration (silviculture & agriculture) Nesting Dunes

22 Fire Suppression & Soybean Field Nesting Dunes

23 Conservation and Management Issues 1) Identify altered habitats that may interfere with orientation and navigation of adults and hatchlings Consequences: impaired i dispersal of hatchlings hli increases a) distance traveled, b) time on land, c) risks (predators, roads, abiotic extremes and not finding aquatic recruitment habitat) 2) Research to determine whether head starting programs that do not allow hatchlings to move to water naturally, subsequently results in impaired i navigation i skills

24 Conservation Measures Identify and protect component areas to promote increased survivorship of embryos in nests and hatchlings during dispersal: a) major nesting areas b) potential refuges for the dispersing hatchlings c) aquatic recruitment areas NESTING AREAS : 1. remove invasives, overgrown woody plants and dense pine stands 2. reduce the extent of agricultural fields and feed plots (for game species) in typical turtle nesting areas and subsidize farmers who increase the years fields lie fallow 3. Use road signs to increase awareness of hatchlings crossing roads and reduce speed dlimits it where high h densities of hatchlings occur

25 Weaver Dunes, MN (600 ha of dune terraces, juveniles abundant, Pop. > 5,000) Valentine Refuge, NB. (29,000 ha of sand hills, juveniles abundant, Pop. ~100,000) E. S. George Reserve, MI (565 ha of old fields and woods, juveniles rare, Pop. ~ 250)

26 Hatchling Blanding s turtles orient toward far dark horizons (Pappas et al. 2009). Hypothesis: Rare occurrence of juveniles and low population sizes in many forested areas (i.e. northeastern populations) are caused by reduced nesting areas and poor hatchling survivorship during dispersal from nests because dark horizons are predominant and not consistently related to the location of wetlands. On the ESGR, nesting areas used by Blanding s turtles are characteristically located where - 1) wetlands are seldom visible from nesting areas 2) near and / or dark horizons are abundant and in all directions

27 There is no magic to it, - protect our habitats!

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29 Weaver Dunes Marshes Dunes Weaver Bottoms

30 Weaver Dunes 2009 Marshes Dunes Weaver Bottoms

31 Road Mortality - male bias - population declines - male bias - population declines

32 Blanding s Turtle Nesting Habitat Pond, Marsh & Potholes Nesting Dune

33 Nesting distances Weaver Dunes (Minnesota)

34 Nesting distances E. S. George Reserve (Michigan) % o f s a m p l e C h e l y d r a s e r p e n t i n a ( n = ) m e a n = m, C V = m in - m a x = m C h r y s e m y s p i c t a ( n = ) 1 0 m e a n = m, C V = m i n - m a x = m E m y d o i d e a b l a n d in g i i ( n = ) 1 0 m e a n = m, C V = m in - m a x = m D i s t a n c e f r o m n e s t t o w e t l a n d ( m )

35 A comparison of body temperatures during dispersal of hatchling Blanding's turtles during experimental releases and from natural nests. % of sa ample A rena (n = 377) Natural (n = 145)l Body temperature ( o C) ple % of sam Hour of day Arena Natural

36 Nesting behavior of females and hatchlings Females: nest dispersal patterns co-evolved ol ed - morphology and physiology (body size, mobility, risk of predation, desiccation rates) - wetland habitat and availability of nesting areas Hatchlings: - morphology and physiology (body size, mobility, risk of predation, desiccation rates, and ability to stay on land for extended periods (yolk reserves) - emergence from nests in Fall or Spring - distance from wetlands - habitats types between nests and wetlands - wetland type (marsh, lake, stream, river)

37 Snapping turtles ( )

38 CS CORN REL 2. NAÏVE - RANDOM NOT SIG DIFF FROM EACH OTHER CS CORN REL 2. NAÏVE - RANDOM NOT SIG DIFF FROM EACH OTHER DEG - NN 0 DEG - DOT DEG - N DEG - A 0 0 DEG - P EB CORN BY CATEGORY - BOTH EXP. ARE NON RANDOM, NAÏVE ARE RANDOM --- ALL CATEGORIES ARE DIFF

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40 Impact of Nesting in Agriculture Fields (turtles with TSD) -Biased population sex ratios (can lower effective population sizes, lead to eggs being infertile, il and over time, increase the potential for population declines) - Increase or decrease in nest depredation d - Altered orientation and nest dispersal impacts hatchling hli survival and population recruitment

41 Snapping Softshells Blanding s Spiny - Smooth Maps Painted Ouachita - Common - False

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