In a Drought, July Showers Bring May Calling

In 1992-93, as concern was escalating about the global decline of Amphibians, we established a system of two auditory monitoring transects north and south from our home in Bishops Mills. This system of 42 stations, plus 'backyard' listening from home,  extends 51 km NNE from just north of Brockville to the north shore of the Rideau River.  As the years went by, it has acquired the moniker “More than one Person can handle,” and with the onrush of other spring-time and summer duties we haven't often been able to listen adequately along the whole transect.  Because of a road we didn't know was impassable when we planned the transects from the topo map, the system has broken down into 3 transects, one to the south, one to the north, and one, most frequently surveyed, around home. When we are home, we also listen from home every night, when it's not excessively rainy or windy, from 1 March to 1 August.

The species referenced here, and the seasons we hear them calling from home (4 & 6 St-Lawrence Street, Bishops Mills, Grenville County, 44.87156N 75.70095W; 1992-2016, a few exceptional outlying years flagged) are: Hylid Treefrogs - Pseudacris crucifer [Spring] Peeper (19 March 2012, 28 March-20 June), & Hyla versicolor [Tetraploid Grey] Treefrog (30 April-18 July [last full chorus]); Catesbianus group Ranid Frogs - Lithobates catesbeianus Bull Frog (18 May 1998, 1 June-10 August), L. clamitans, Green Frog (24 May-13 August), & L. septentrionalis, Mink Frog (24 May-1 August); and [American] Toad, Anaxyrus americanus, (19 March 2012, 2 April-19 June [last full chorus] -20 July [last calls]).

Three appropriately timed surveys on nights with appropriate weather can get good records of all Anuran species calling in eastern Ontario, but one of the lessons we've learned, in what's now 34 years of experience, is that good seasons for frogs are often bad for auditory monitoring. The best seasons for listening to spring-calling species are those in which the temperature warms gradually, with modest precipitation and moderate week-long oscillations in temperature. On the other hand, the best seasons for these frogs are those in which warming and wetness coincide, to bring the all the females to the ponds in a single wave, so mating is concluded promptly, and both sexes spend a minimum of time and energy reserves in completing the breeding, with maximum survival to breed again in a subsequent year. This scenario minimizes the duration of calling, and severely constrains the time available for auditory monitoring. 

On the other hand, persistently dry seasons can be bad for both frogs and monitors, since choruses are late in forming if small species, particularly, won't move across dry ground to reach breeding ponds, many of the frogs may desiccate on the way to the ponds, peak calling may occur on very different dates at different sites, and some ponds may dry up during the calling season. Similar but less easily understood factors seem to influence calling by Mink/Green/Bull Frogs; one that is fairly easy to grasp is that calling is prolonged, for Green & Bull frogs at least, during  dry seasons, in which it seems that males continue to call after breeding is finished to defend territories for feeding, whereas in wet summers they abandon the wetlands for terrestrial foraging (hypothesis 3 of Schueler 2000).

In 2016 maps of conditions show record low precipitation in the area of the surveys, and “In Ottawa, counting both snow and rainfall for [1April to 28 July], the area has received only a little over half the normal amount seen there from April through July. Based on Environment Canada weather records, Ottawa International Airport recording its 2nd lowest precipitation total for the growing season... since record keeping began there in 1938, second only to the same period in 1955.”[1] This season we had support from the OFNC Research Fund for driving the transect, which was an incentive to push other obligations aside and go out frequently. A problem in listening along a transect which you can't monitor every night is deciding on which nights you're going run the transect, since you're trying to hear all the species that can be heard from each station, and calling intensity, especially at stations where the calling is from distant sites, is diminished by low temperatures and changed by moisture levels. 

Methodology:  At each station we follow our 1994 auditory monitoring protocol: “Record the time you listened, air temperature, wind and precipitation, sources of distracting noise, and species that were calling (or that none were heard)... we record all anurans, birds and mammals that we hear and all amphibians and reptiles we see while we are listening. Intensity of calling is indicated by the Wisconsin calling index (Index One = Individuals can be counted; no overlapping of calls. Index Two = Calls of individuals are distinguished, but some calls overlap. Index Three = Full chorus; continuous calls) or by counts of individuals. We listen at a station until we are satisfied that we have heard all calling anuran species, usually 2-5 minutes, but sometimes as long as 10 minutes if there is a lot of noise. We record starting and finishing times of the visit; air temperature and wind, sky and distracting noise are described at each stop.” (page 153, Karstad, et al. 1995).

Because of the uncertainty of when to go out when conditions were so dry, and continually waiting for rain, we had a hard time deciding when to go out through May, because the nights were cold and the days not warm, and there were no rainy nights.  Through June there were 6 days when there was some rain, and it rained a bit on 2 July, but the plants were transpiring heartily, and on 8 July the roadside ditch just south of Bishops Mills, was crisply dry, with herbs on the floor of the ditch all wilting. The night before I'd run the nearby transect, and had heard only relatively unenthusiastic Bull, Green, and Mink Frogs. That night (22h19,22h36, 20.7°C, overcast, Beaufort gentle-light breeze) a few Bull Frog calls were audible from home, over radio noise from the neighbour's barn (the radio is run to scare Pigeons, Columba livia, away from the barn).

In the wee hours of 9 July, 02h30-02h40, we had the onset of forecast rain with thunder. This continued until about 4 cm fallen (29.2 mm total at the Environment Canada rain gauge in Kemptville, half of the rain measured there in all of July), and then on and off all day. At 15h18-15h26, as I “did the streets” in the village for on-road creatures, it was 20°C, calm, with light rain and thunder, and there were fresh skins of three Green Frogs and a Toad dead on the streets. The creek had about twice the minimal flow it had had the day before, and formerly dry garden soil was moist to a depth of 30 cm.

After dark, there was a moderate surrounding chorus of Treefrogs, heard over radio & traffic noise in a trace of rain.  Rain continued through the night with juvenile Green Frogs (8 alive on road, 5 dead on road), Treefrogs (2 AOR, 2 DOR), 1 DOR juvenile Storeria occipitomaculata (Redbelly Snake), and 3 Cepaea nemoralis snails active on the sidewalk. On the next day there were 8 DOR and 3 AOR juvenile Green Frogs, and 3 DOR and 1 AOR yearling Treefrogs on the streets.

Having heard Treefrogs and Toads from home on 10 July, I set out to repeat the listening I'd done on 7 July. The results are presented in the Table below. On this nearby circuit, 14 stations are visited, at temperature of 20-18°C (22h47-25h02) on 7 July, & 14-12°C (22h45-25h02) on 9 July, clear and calm on both nights. The time of visits overlapped or was adjacent minutes at 10 stations, and was less than 10 minutes different at the others, so comparisons between the nights don't reflect changes in intensity of calling through the nights (this precise temporal matching was purely fortuitous, and was not planned). Air temperatures varied in parallel among stations, and was 6°C cooler on 10 July at 8 stations, 5°C cooler at 4, and 7°C cooler at two.

The most widespread change after the rain was reduced calling by Green and Bull frogs (reduced scores for Bull Frogs at 9 stations, for Green Frogs at 5; Green Frogs not heard where they had been heard on 7 July at 6 stations, Bull Frogs at 1;  Green Frogs heard where they had not been heard on 7 July at 1 station).  The closely related Mink Frog was heard at two stations where it had not been heard on 7 July.

Spring-calling species which were only heard after the rain were Treefrogs (5 stations), Peepers (4 stations), and Toads (4 stations). Treefrogs hadn't been heard since 28 June, and the resumed calling went on until 24 July; Peepers hadn't been heard since 27 May, and weren't heard again until fall calling began. Toads hadn't been heard within the area of the circuit since 15 June, and weren't heard again.

Discussion: The reduced calling by Green and Bull Frogs may have been due to the lower temperature on the 10th  or it may have been due to males abandoning calling for terrestrial foraging in the newly dampened surroundings of the water bodies. This latter idea may be supported by the lack of decline in the calling of the resolutely aquatic Mink Frogs, and the number of Green Frogs found on the streets, 300 m from the nearest water, though none of the ones that reached the village were adult males that would have been calling.

In normal springs, Treefrog calling is more or less continuous between the calling at the breeding ponds, calling during dispersal from the ponds, and calling from the trees of the summer habitat. There's more calling in rainy summers, and one of their vernacular names is Rain Frog, but there's also fluctuations in abundance, and understanding the meaning of their summer calling will call for a detailed analysis. This year, after the rain, calling tapered off during 11-12 July, with some also heard on 17 and 24 July as the drought continued.

July calling by Toads isn't unknown, we've had it locally in 2003, 2004, 2008, 2009, and 2013; these seem to be isolated males from the shores of the creek or other water bodies, but we've never gone out and found any of the July-calling males.

This is the first time we've had calling by Peepers in early July -- all previous July records have been late in the month, a few days before the traditional onset of fall calling on 1 August. In this case we have to assume they were jolted into calling by the novel sensation of rain -- or perhaps they were holed up partway along the routes to summer habitat, and were calling as they they would have at those same locations in a normally wet spring while dispersing from the breeding sites towards summer habitat.

The interesting thing about this unseasonable calling is that, unless there were some very late-season female Toads, it's all unassociated with breeding. The functions of autumnal calling are hard to study, but the suggestions are either hormonal urges left over from, or preparing for breeding, or else territorial spacing during the feeding season.

Climate change is supposed to increase the irregularity and intensity of droughts, and we'll need both  regular monitoring and careful analysis of the gathered data to understand its effects on our Amphibians.

Documents Cited
Karstad, Aleta, Frederick W. Schueler, and Lee Ann Locker. 1995. A place to walk: A naturalist's journal of the Lake Ontario Waterfront Trail.  Natural Heritage/Natural History, Toronto. 159 pp.

Schueler,  Frederick W. 2000.Three patterns of seasonal movement among Eastern Ontario Rana. CARCNET 5th Annual Meeting, Penticton, British Columbia, 22-25 September 2000.

Table: Calling before and after drought-breaking rain of 9 July 2016.  

Names of Anuran species not heard on the other night bolded.
7 July 2016 (before rain)
10 July 2016 (after rain)
Bishops Mills:4 & 6 St Lawrence St. (home). 44.87156N 75.70095W rural village, shallow soil limestone plain.
22h27-22h31, 21.4°C, clear, calm. Bull Frog, index3? nearly inaudible chorus; Green Frog, index? nearly inaudible calls.

25h05-25h10.  18°C, clear, calm; truck thermometer 18°C, wall-mounted remote thermometer 18.5°C. Green Frog, index3  surrounding chorus; Bull Frog, big surrounding chorus.
21h26,21h35.  16°C, clear, calm. Treefrog, index2-3 moderate surrounding chorus; Dumatella carolinensis (Catbird) 1 singing loudly from across Co Road 18. No Robins (Turdus migratorius) calling now.

22h36-22h40.  15°C, clear, calm.  Treefrog, index2-3 moderate surrounding chorus, Toad, index1  few calls, airplane, traffic & radio noise. Blink Beetle, very few blinking.

25h08-25h11.  13.5°C, clear, calm.  Treefrog, index1 few calling, loud radio noise.

25h33.  12.5°C, overcast, Beaufort light breeze.  Treefrog) . 1-2 calling; Bull Frog, index1  few calling, loud radio noise.
Kemptville Creek/Co Road 20, 0.1 km SE Co. Rds 18 & 20. 44.90086N 75.68290W  swamps & marshes along slow brownwater creek.
22h47-22h51. 19°C, clear, calm. Bull Frog, index1 few intermittent calls; Green Frog, index1 few calls; Mink Frog, index1 very few calls; Blink Beetle, very few blinks.

22h45-22h49. 14°C, clear, calm. Bull Frog, index1 very few unenthusiastic calls; Green Frog, index1 very few unenthusiastic calls; Mink Frog, index1,  very few unenthusiastic calls; Peeper, 1(+?) calling,  1 calling at a time.
County Road 18 at Hutchins Corners/ Kemptville Creek.  44.92831N 75.69467W creekside Red Maple swamp, Typha marsh/hayfields.
22h59-23h01. 20°C, clear, calm. Bull Frog, index3 chorus; Green Frog, index2-3 moderate chorus. No Mink Frog calls distinguishable, but calling is loud and not nearby.

22h54-22h58.  14°C, clear, calm. Bull Frog, index1,  few calls; Green Frog, index1 very few calls; Mink Frog, index1 very few calls, traffic noise; Blink Beetle, very few blinks.
Jig St/County Road 18.  44.91033N 75.69129W  — brushy oldfields, hayfields, swampy creek.
23h07-23h11. 20°C, clear, calm.  Bull Frog, index2 intermittent chorus; Green Frog, index1-2  small chorus; Blink Beetle, very few blinks.
23h03-23h06.  14°C, clear, calm. Bull Frog, index1 very few faint calls; Green Frog, index1 very few faint calls.

Jig St/Concession VII.  44.90122N 75.70891W  — pasture, oldfield, Aspen thickets, roadside ditch.
23h15-23h19. 19°C, clear, Beaufort light air. Bull Frog, index? nearly inaudible calling; Green Frog, index? nearly inaudible calling, Culicid noise; Blink Beetle, few blinking. As usual for this site, this was the most seen tonight.
23h03-23h06.  14°C, clear, calm.  Bull Frog, index? calling,  nearly inaudible calling; No Blink Beetles seen.

Jig Sreet/Hare Hill Road.  44.87867N 75.71496W — agricultural hay/corn/oldfields.
23h25-23h29. 19°C, clear, calm.  Bull Frog, index1 very few calls from creek, loud airplane noise - a total of 6 planes going over.
23h17-23h21.  13°C, clear, calm.  Toad, index1 few calling from 2 or more directions; Treefrog, index1 calling,  few calls from various directions, highway noise.
South Branch Kemptville Creek at South Branch.  44.81395N 75.70025W — slow creek, creekside meadows, farms, pasture/tilled.
2342-2347. 18°C, clear, calm.  Bull Frog) . index2-3 intermittent nearby chorus, no Mink Frogs heard; Green Frog, index3 calling,  nearby chorus, water aswarm with frogs; Blink Beetle, very few blinking.
23h38-23h42.  13°C, clear, calm. Bull Frog, index1 very few calls; Green Frog, index1 very few calls; Toad, 1(+?) calling,  3 calls, loud fuzzy machinery noise.

Diamond Rd/ Kemptville Creek, S of Co 18/Branch Rds.  44.82760N 75.67638W — slow creek, creekside meadows, Ash forest, adjacent farms.
23h53-23h58. 18°C, clear, calm. Bull Frog, index1  few calls, No Mink Frogs heard; Green Frog, index1  few calling, lots of frogs by eyeshine; Ardea herodias (Great Blue Heron), 1 calling with squawks; Blink Beetle,  very few blinking.
23h49-23h54.  12°C, clear, calm. Bull Frog, index1  very few calls; Green Frog, index1  very few calls; Peeper, index1 very few calling, 1-2 at once; Toad, index1 few calls; Treefrog, index1 few calling, airplane noise; Blink Beetle, very few blinking.
Garretton, Co Road 18 at Kemptville Creek.  44.83851N 75.65753W  — marshy creek, meadows, pastures, residences.
24h03-24h08. 19°C, clear, calm.  Bull Frog, index1-2 small intermittent chorus; Green Frog, index1-2 small chorus.
23h59-24h04.  13°C, clear, calm, foggy. Bull Frog, index1 very few calls; Green Frog, index1  very few calls; Toad, index1 very few calls; Peeper, index1 very few calls, from 1 at once, with some trills; Strix varia (Barred Owl) hooting 'cooks-for-you' persistently. Moonset.
Cooper Road, 4.2 km SE Bishops Mills.  44.84930N 75.65892W  — Ash/Acer swamp, Aspen/Thuja thickets, roadside ditches.
24h13-24h17.  20°C, clear, calm. Bull Frog, index3?  distant chorus; Blink Beetle, few blinking.
24h08-24h11.  13°C, clear, calm.  Bull Frog, index1 few barely audible calls; Green Frog, index1 few barely audible calls. No nearby calling; Barred Owl, 1 calling,  hooting 'cooks-for-you' persistently. Likely the same one heard from Garretton. With the Moon set, the Milky Way is now visible.
Cooper Road, 5 km ESE Bishops Mills.  44.85840N 75.64257W  — Thuja/Salix swamp, Pine plantation, roadside ditch.
2422-2425.  20°C, clear, calm.  Bull Frog, index1-2  intermittent small chorus; Green Frog, index2 small chorus; Blink Beetle, few blinking.
24h24-24h28.  13°C, clear, calm. Bull Frog, index1 barely audible small chorus; Treefrog, index1 few calls; Blink Beetle, very few blinks, maybe just one female on the ground.
Dawson Trail at Cooper/ Limerick Rds, Limerick Forest.  44.87425N 75.65531W — track through Pine plantation/ shallow ditch/brushy roadside.
2431-2434. 19°C, clear, calm. Green Frog, index3 chorus in 'the Swamp' E of site; Blink Beetle, very few blinking.
24h33-24h35.  13°C, clear, Beaufort light air.  no observation, no calling actually audible, though one could imagine Treefrog, Peeper, and Bull Frog.

Kemptville Creek/ Limerick Road. 44.86115N 75.67945W — bridge embankment, brown-water creek, Cephalanthus swamp.
24h38-24h46. 18°C, clear, calm. Bull Frog, index3 chorus; Green Frog, index3 chorus;  Blink Beetle, very few blinking.

24h40-24h46.  12°C, clear, calm. Bull Frog, index2  small loud nearby chorus; Green Frog, index1 few calls; Mink Frog, index1 very few standard calls, but this species may have produced a few 'glumph' and 'blurt' calls; Peeper, index1 very few calling.
County 18/Limerick Rds, 1.9 km SE Bishops Mills. 44.85814N 75.68687W  — Aspen/Thuja woods,  Aspen/Salix/Larix swampy brush/ tilled fields.
24h48-24h52. 19°C, clear, calm.  Green Frog, index3  big chorus along creek; Bull Frog, index3 chorus along creek; Canis latrans (Coyote), distant howls hard to hear over Bull & Green frog chorus.
24h48-24h52.  13°C, clear, calm. Bull Frog, index1  faint chorus from creek; Treefrog, 1(-2?) calling,  2 recognizeable calls.
Bishops Mills Bridge, Middle Creek/Mill Street.  44.87423N 75.70478W —  riffles of slow creek, rural village, fields.
24h58-25h02. 18°C, clear, calm. Bull Frog, index3 chorus up- & down-stream, none nearby; Green Frog, index1  few calls, swamped by Bull Frog chorus.

24h59-25h02.  13°C, clear, calm. Bull Frog, index1 few calls from downstream; Treefrog, 1? calling,  few calls from upstream, whirring machinery noise.


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