Leopard Frog Predation on Emerging Adults of Colonizing Variegated Meadowhawk Dragonflies David J

LEOPARD FROG PREDATION ON EMERGING ADULTS OF COLONIZING VARIEGATED MEADOWHAWK DRAGONFLIES David J. Larson Box 56 Maple Creek, SK S0N 1N0 [email protected] The early spring of 2016 was very dry in southwestern Saskatchewan. The soil was dry the previous fall and very little snow fell over the winter. Spring melt occurred with no runoff so vernal ponds were empty and water levels in dugouts and dams were low. At a period with so much concern about climate change, one could not help but wonder if this drought presaged future dry conditions. At any rate, it is never a bad idea to try to improve water security. The dry soil meant that heavy equipment could operate without doing too much damage. We hired a track-hoe to come in late April to FIGURE 1. Cactus Flats Dam with water level near capacity. Dragonfly and frog observations were made along dig a dugout and make two dams. the shorelines where the grass was flooded. Photo credit: D. Larson These observations relate to the larger of the dams, which we called and prairie muhly on sandy-clay soil. I took great pleasure in visiting the Cactus Flats Dam in recognition of The term potentially is used because dam each day to watch the water the habitat that was destroyed in our feeling was that it would take level rise. Immediately on holding its construction. It is located on the several years of accumulated runoff water, new life appeared. On the north slope of the Cypress Hills (SW to reach the outflow culvert level, if first night of there being water, an 28 09 26 W3), about 14 km S of ever. invasion of larger water bugs, most Maple Creek. The weather changed — there notably backswimmers (Notonecta), The dam was built at the was a little rain and snow in late and water beetles (Acilius, confluence of two small coulees that April, just during the last phases of Graphoderus and Rhantus) occurred. cut through Bearpaw age bedrock construction, that put more than 1 m Smaller water boatmen (Corixidae) consisting mainly of clays and shales of water into the basin of the dam. and water beetles (Dytiscidae, with lenses of sand and gravel. The Over the next several weeks, heavy Gyrinidae, Hydrophilidae) quickly coulee bottom was an alluvial pan rainfalls (e.g. more than 60 mm on followed. Shore flies, small ground of white clay with sparse vegetation May 9 and 10) added more run-off beetles (Bembidion), rove beetles, of mainly western wheat grass, and by mid-July the dam was close to variegated mud-loving beetles and cacti and sagebush. On completion, full. Most of the pond was 4 to 5 m shore bugs populated the mud the water depth could potentially deep but there were shallow margins at the water's edge. Chironomid average 5 to 6 m in a pond about 75 where the sparse grasses had been flies and mayflies (Callibaetis sp.) by 50 m, and flood up the side walls flooded to give an emergent zone of swarmed along the waters edge of the coulee into a mixed grassland drowning arid land plants along the and oviposited over the water. community of gramma, needle grass, shoreline (Fig. 1). Microcrustaceans became apparent, 16 BLUE JAY SUMMER 2017 VOLUME 75.2 first shoreline swarms of copepods its larval development completed by then later of daphnia. Changing August 16. Most local meadowhawk water color indicated various algal species do not occur as adults in the blooms, filamentous algae formed spring — they are summer to fall a mat along the shorelines and species and a rough rule of thumb duckweed colonized protected is that any small pond dragonfly embayments. seen in spring and early summer is a Dragonflies appeared, most whiteface (Leucorrhinia species) and abundant were small blue damselflies in summer and fall is a meadowhawk that perched on emergent grass species. I resolved to return the next stems along the shoreline or that day to see if I could find a male, paired up in tandem sets in mating preferably one with sufficiently hard and egg laying. Larger dragonflies cuticle that it would be suitable for were less abundant but were identification and preservation as a more conspicuous, especially the voucher specimen. spectacularly patterned Twelve- On August 17, the shoreline of spotted Skimmer (Libelulla pulchella). the dam had numerous exuviae Amphibians also appeared. A few (the cast cuticle left behind when Striped Chorus Frogs (Pseudacris an insect moults, Fig. 2) and some FIGURE 2. Exuvium, shed larval cuticle, of the triseriata) called from amongst a newly emerged dragonflies. They Variegated Meadowhawk dragonfly. dense patch of flooded grasses had probably emerged overnight Photo credit: D. Larson but this lasted only a few days and for at 09:00 h some specimens no eggs or tadpoles were found. were leaving the shoreline area in abdomen; and sets of dragonfly Occasionally in the deeper water the weak fluttering first flight of a wings (presumably a dragonfly some larger creatures rolled or newly emerged dragonfly. I checked eaten by some predator that left thrust their forebody up out of the out a number of specimens near the the wings)). The frogs counted were surface. These were probably Tiger water's edge to find one suitable those that flushed when a step was Salamanders (Ambystoma tigrinum) to collect but all were too teneral. I made; the various dragonfly stages as they occur in a neighbouring would have to find a specimen that were those seen within the area in dam. Northern Leopard Frogs (Rana had flown from the pond and had front of me that could be carefully pipiens) were very common from July a more hardened cuticle. However, searched without moving my feet, into early October when there was what I did notice was several roughly 1 m2. Two 25-pace transects a heavy snowfall. However, a few dragonflies had no abdomens — were walked but dragonflies were reappeared later and the last was they had been decaudated (Figs. counted on only one. The second seen in mid-November. 3, 4, 5). They were still alive and transect had such dense grass that Daily observations of this vein clinging to grass stalks but were exuviae could only be found by were made over the summer. On immobile. If prodded to move they laborious searching. The counts were August 16, there was a teneral were unsteady and could not fly. made between 10:00 and 12:00 h, (a newly moulted insect in which Also, leopard frogs were abundant and the day was sunny and warm the cuticle is soft and usually pale) and I wondered if these were with a light SW wind. The results are female specimen of a small dragonfly the culprits that had injured the given in Table 1. On a return visit the — a meadowhawk (Sympetrum) dragonflies. following day (August 18), no new species. This specimen seemed most In order to get a better measure exuviae or teneral specimens were unusual as species of meadowhawk on what was observed, a simple observed so the counts were not are abundant in local ponds but count was conducted that consisted repeated. generally have a one-year life cycle of walking a line 1 m back from The results of the survey indicate with eggs laid one summer emerging the edge of the pond and at each that there were more exuviae than as adults the following summer. This pace (a little less than 1 m but a dragonflies. The exuviae were not dam was not present the previous close approximation) stopping and present (at least not noticed) on the summer, the dragonfly had to have counting frogs, and dragonflies (as previous morning (August 16) and been laid as an egg after May and exuviae; tenerals; tenerals with no they probably represent overnight SUMMER 2017 VOLUME 75.2 BLUE JAY 17 FIGURES 3, 4, 5. Variegated Meadowhawk, teneral adults that had been decaudated (abdomens removed). Photo credit: D. Larson emergence (August 16/17) with most cent based on remains (wings) and would be helpless, easy prey and the new adults flying away from the injured (decaudate) specimens. If thorax with its large flight muscles pond before the count was made in entire insects (either or both nymphs would be the most nutritious part the morning. This was supported by and adults) were consumed, this of the insect. If a frog was acting observation of teneral but airworthy mortality estimate would be too low. as an ambush predator, the act of dragonflies both on vegetation I accuse the leopard frogs (Fig. 6) snapping the abdomen off a moving, and flying at distances of several as being the predator. This is based teneral dragonfly would traumatize hundred metres or more downwind on not seeing any other potential the dragonfly and probably render from the pond. A voucher specimen predator. Two Lesser Yellowlegs it immobile, at which point the frog was collected from among these. and one Spotted Sandpiper were may not recognize the inert body as This corresponds to the observation present on the morning of August prey and not continue the attack. of Hutchings and Halstead that 17, but their foraging was along The dragonfly was identified dragonflies tend to emerge under barren, muddy shorelines and not in as Variegated Meadowhawk the cover of darkness as it reduces the grass. A sparrow (unidentified, (Sympetrum corruptum (Hagen)) (Fig. the likelihood of predation.1 The possibly a Savannah Sparrow) was 7). This species has a wide range newly emerged dragonflies must seen in shoreline grass on the in North America extending from have dispersed rather quickly from other side of the pond but not in Mexico north into the boreal zone the pond edge into the surrounding the survey area, although there of the Prairie provinces, although grasslands.

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