Abstract

Transmitters may have deleterious effects on wild ducklings which may make them more susceptible to mortality from starvation, chilling, exhaustion, predation, and parasites. Captive studies report nil to little effect of transmitters but ducklings in those studies were maintained in ideal conditions. In contrast to other captive studies, this research suggests back-mounted radio transmitters with a subcutaneous anchor have a negative effect on duckling growth, behavior, and survival.

Introduction

Waterfowl broods are difficult to monitor during their first 2 weeks of life because of high mobility and low visibility.^7,13 To overcome these obstacles, researchers rely on radiotelemetry as a tool in brood ecology. Most radiotelemetry studies on brood survival and duckling survival have employed radio-marked adult females with broods.⁵ In wild ducklings, brood cohesion can make it extremely difficult to distinguish duckling and brood mortality from brood abandonment.³ Therefore, more accurate measurements of duckling fate can be achieved by radio marking individual ducklings within the brood.^11,15

Transmitters may have deleterious effects on wild ducklings which may make them more susceptible to mortality from starvation, chilling, exhaustion, predation, and parasites.^1,3,14 Ducklings raised by wild mallards (Anas platyrhynchos) are often moved over land considerable distances within the first few days of life, they must forage for food and rely on the female for warmth.^1-4,14 Studies of wild duckling survival have conflicting conclusions on the impact of back mounted radio transmitters. Some studies report little impact from the transmitters,⁸ while other studies report very high mortality¹⁰. Sublethal effects of the transmitters may include suboptimal growth which may reduce long-term survival of juveniles.⁶ If radio transmitters have an impact on duckling growth and survival, results of studies done on wild ducklings may be less meaningful. Conservation efforts will be more likely to succeed if they are based on more reliable knowledge.

Captive studies report nil to little effect of transmitters but ducklings in these studies were maintained in ideal conditions. Ducklings were housed without the female, were provided with ad libitum food, and had access to an artificial heat source.¹⁶ Therefore, the purpose of this study was to determine the effects of transmitters applied to day-old ducklings by evaluating behavior and weight gain postoperatively in a seminatural environment.

Materials and Methods

Five broods (36 ducklings) were hatched by adult female mallard ducks housed in outdoor pens at St. Denis Wildlife Refuge, SK, Canada (52°13’N, 106°04’E). Females were housed individually in pens measuring approximately 3×10 m comprising of 70% brome grass and 30% artificial pond. Water was pumped from a nearby pond as needed to maintain water levels. Day-old ducklings were divided randomly into two matched groups where half the ducklings in each brood received back-mounted transmitters (1.8–2.0 g) with a subcutaneous anchor¹¹ (transmitter group), and half the ducklings did not receive a transmitter but were handled for the same amount of time (control group). Anchors were placed subcutaneously through a 5-mm incision after injection of lidocaine at the surgical site. The incision was closed, and the anchor was sutured in place with 4.0 silk. All ducklings had web tags placed after topical administration of lidocaine for individual identification.

Ducklings were weighed prior to transmitter attachment, daily for the first week, and every 2 days thereafter for 30 days. To mimic natural environmental conditions where ducklings are moved over land by the female, food was restricted to 75% of energy requirements for duckling growth for the first 2 days and 110% for the remainder of the experiment. Access to an artificial pond containing invertebrates was not limited and ducklings were exposed to normal daily environmental conditions. All ducklings with radio transmitters and one randomly chosen control duckling from each brood were euthanatized humanely at end of experiment. Euthanatized ducklings and ducklings found dead had complete necropsies and histology. Results from necropsies will not be discussed.

Ducklings were observed or video recorded for a minimum of 30 minutes daily for the first week. Only observations done for the first week will be discussed. Behavior of each treatment group was recorded every minute as locomotion (walking or swimming), foraging, comfort behavior (preening, stretching), resting (sleeping, sitting, or loafing), or out of sight (not visible to the observer). The behavior of the majority of ducklings for each treatment group was considered the behavior of that group. Each behavior was calculated as percent of time spent performing the above behaviors as matched groups in each brood. In addition, every preening event was recorded, and each event was separated by a different behavior. Preening was calculated as preening event/duckling/minute.

Survival data were analyzed with a Fisher’s exact test. Duckling behavior (transmitter groups verses control groups) were analyzed using Wilcoxon matched pairs signed ranks tests since distributions were non-normal. Duckling weights were analyzed using Student’s t-test. A difference was considered significant at p≤0.05.

Results

Five ducklings (four females and one male) that received transmitters died and one female duckling in the control group died (Table 1). The mean time to death was 3.5 days. Deaths of ducklings in the transmitter group was significantly greater than ducklings in the control group (Fisher’s exact test, 1-tailed, p=0.0403). Six ducklings from three broods escaped from the pens and were excluded from the study after escape. All ducklings lost weight following hatch. Female ducklings in both the transmitter and control groups took 6 days to gain weight to match or better hatch weight. At day 6, female ducklings in the transmitter group were 2 g lighter than ducklings in the control group. Male ducklings in the control group took 5 days to match or better hatch weight while ducklings in the transmitter group took 6 days. Female ducklings in the transmitter group weighed less than ducklings in the control group from day 1–30. There was no significant difference between hatch weight in females (Student’s t-test, p=0.2). Male ducklings with transmitters were significantly heavier at hatch (Student’s t-test, p=0.05) but were lighter than ducklings in the control group from day 9–30.

Table 1. Survival of mallard ducklings after placement of a radio transmitter with a subcutaneous anchor

Ducklings with transmitters preened the surgical area more often (0.08 preening events/duckling/minute) than ducklings without a transmitter (0.01 preening events/duckling/minute Wilcoxon test, 1-tailed, p=0.04). Ducklings with transmitters were also observed shivering and pulling on the transmitter body and antenna. The hen was observed stepping on the antenna, preventing ducklings with transmitters from moving on several occasions. Although no statistical difference was found in other aspects of behavior, some trends observed may become significant when sample size is increased. Ducklings with transmitters spent more time out of sight (12%) and less time foraging (14%) compared to ducklings in the control group (5% and 17%, respectively).

Discussion

In contrast to other captive studies, this research suggests back-mounted radio transmitters with a subcutaneous anchor has a negative effect on duckling growth, behavior, and survival. Ducklings with transmitters had higher mortality, decreased weight gain, and preened more frequently than ducklings without transmitters. In addition, ducklings with transmitters spent more time out of sight and spent less time foraging. Ducklings with external transmitters show areas of increased surface temperature in thermographic images suggesting that heat loss may be increased in ducklings with transmitters.² Thermal effects may be significant for ducklings because of small body size, limited thermogenic capacity, and relatively ineffective insulation.^2,9 Transmitters may also disrupt the plumage,¹² thereby, increasing thermoregulatory costs in cold, windy weather. Increased heat loss, demonstrated by shivering, may have resulted in hypothermia and death of the five ducklings that died with transmitters. In addition, ducklings with increased heat loss may not gain weight effectively. Ducklings may seek more sheltered areas of the pen which may have been demonstrated in more time spent out of sight. Energy requirements of maintaining body temperature may result in decreased foraging activity and thus, lower body weights.

Although results from this study are preliminary, there appears to be some important survival growth, and behavioral changes of ducklings with radio transmitters compared with ducklings without transmitters. Further research is required to increase sample size. This study will be completed during the 1998 field season.

Acknowledgments

This research was supported by the Canadian Wildlife Service, Delta Waterfowl Foundation, and the Wildlife Health Fund, University of Saskatchewan. I would also like to thank my supervisor Dr. Alex Livingston and Dr. Robert Brua for their assistance in writing this abstract. Special thanks to Lise Tellier for technical support during this study.

Literature Cited

1.  Amlaner, C.J. 1978. Biotelemetry from free-ranging animals. In: Stonehouse, B. (ed.). Animal Marking Recognition Marking of Animals in Research. University Park Press. Baltimore, MD. 205–228.

2.  Bakken, G.S., P.S. Reynolds, K.P. Kenow, C.E. Korschgen, and A.F. Boysen. 1996. Thermoregulatory effects of radiotelemetry transmitters on mallard ducklings. J Wildl Manage. 60:669–678.

3.  Brown and Hunter. 1984. Potential effects of insecticides on the survival of dabbling duck broods. J Minn Acad Sci. 50:41–45.

4.  Duncan, H.A. 1986. Survival of dabbling duck brood on prairie impoundments in southeastern Alberta. Can Field Nat. 100:110–11.

5.  Grand, J.B., and P.L. Flint. 1996. Survival of northern pintail ducklings on the Yukon-Kuskokwim delta, Alaska. Condor. 98:48–53.

6.  Haramis, G.M., J.D. Nichols, K.H. Pollock, and J.E. Hines. 1986.The relationship between body mass and survival of wintering canvasbacks. Auk. 103:506–514.

7.  Hill, D.A. and N. Ellis. 1984. Survival and age related changes in the foraging behaviour and time budget of tufted ducklings Aythya fuligula. Ibis. 126:544–550.

8.  Korschgen, C.E., K.P. Kenow, W.L. Green, D.H. Johnson, M.D. Samuel, and L. Sileo. 1996. Survival of radiomarked canvasback ducklings in northwestern Minnesota. J Wildl Manage. 60:120–132.

9.  Koskimies, J., and L. Lahti. 1964. Cold-hardiness of the newly hatched young in relation to ecology and distribution in ten species of European ducks. Auk. 81:281–307.

10.  Krapu, G.L., P.J. Pietz, and D.A. Brandt. 1997. Use of landscape formation to predict survival rates of mallard and gadwall broods and ducklings in prairie pothole habitat. In: Proceedings of the First North American Duck Symposium, Baton Rouge, LA, 35–36.

11.  Mauser, D.M., and R.L. Jarvis. 1991. Attaching radio transmitters to 1-day-old ducklings. J Wildl Manage. 55:488–491.

12.  Perry, M.C. 1981. Abnormal behavior of canvasbacks equipped with radio transmitters. J Wildl Manage. 45:786–788.

13.  Ringleman J.K., and L.D. Flake. 1980. Diurnal visibility and activity of blue-winged teal and mallard broods. J Wildl Manage. 44:822–829.

14.  Seymour, N.R. 1982. Mortality of duckling attributed to separation from mother and subsequent protracted exposure to low ambient temperature. Auk. 99:383–384.

15.  Talent, L.G., R.L. Jarvis, and G.L. Krapu. 1983. Survival of mallard broods in south-central North Dakota. Condor. 85:74–78.

16.  Zenitsky, GD. 1993. Growth and Behaviour of Redhead Ducklings Implanted with Dummy Radio Transmitters. MSc Thesis, Iowa State University, 137.