Indian Journal of Experimental Biology Vol. 42, October 2004, pp. 1013-1016

Evaluation of secondary poisoning of difethialone, a new second-generation anticoagulant rodenticide to Bam owl,

Tyto alba Hartert under captivity

K Saravanan* & R Kanakasabai**

PG & Research Department of Zoology & Wildlife Biology, A.V.C. College (Autonomous), Mannampandal609 305, India

Received 21 October 2003, revised II June 2004

Secondary toxcity of difethialone to Barn owl (Tyto alba) has been investigated. Difethialone was fed to owls for successive periods of 1 (phase 1), 3 (phase 2) and 6 (phase 3) days via­rodenticide dosed rats. The owls survived after the treament of rodenticide on phase 1 and phase 2 experiments but they died during phase 3 experiment. The results suggest that the difethialone could cause more secondary toxicity to owls.

Keywords: Anticoagulant; Rodenticide; DifethiaIone; Secondary posioning; Barn owl, Tyto alba.

Rodents are important vertebrate pests in agriculture fields of India. Though different methods have been adopted by farmers and scientists to control the rodent pests, rodenticidal baiting is in practice due to quick efficacy and cost worthiness I ,2. Not only the rodenticides are more active and persistent in the target species they also have a greater potential for secondary poisoning of rodent predators3

-s, For any rodenticide, the

secondary hazard, which may arise through the consumption of poisoned rodents, depends on the quantity of active ingredient present in live and dead rodents and the opportunity for these rodents to be eaten by non-target animals6

•

The Barn owl, Tyto alba Hartert is a night hunting predator that feeds on live rodents and birds4 and may therefore be at risk from the use of rodenticides. World wide decline in Barn owl population due to rodenticide poisoning has been reported7

-lo

, In southern India, Barn owl extensively feeds on rodent pest species viz., Bandicota bengalensis, Mus

Present address: * Department of Zoology, Nehru Memorial College, Puthinampatti 621007, Tiruchirapalli Dist. **Shree Ragavendra Arts & Science College, Keezhamoongiladi, Chidambaram 608 102, India Phone: 04144-232774;232775: E-mail: ratsaro@yahoo.com

booduga, Millardia meltada, Tatera indica and Rattus rattus11 and the farmers use a wide variety of rodenticides to control the rodent pests in the agricultural fields 12.

Difethialone ([(Bromo-4' -[biphenyl-l-l ']-yl-4)-3, tetrahydro-I-2-3-4-naphthyl-l]-3 hydroxy-4-2H-l-l­bentothiopyran-one-2) a new second generation anticoagulant rodenticide is reported to be more toxic to major rodent pests of Indian subcontinent in laboratory and wild I3

-18

. However, no study has been undertaken in India to evaluate the secondary poisoning of difethialone on the non-target organism viz, Barn owl. Hence, this preliminary baseline study has been attempted to evaluate the secondary poisoning of difethialone on Barn owl under captivity by using difethialone dosed rats.

Adult Barn owls (3 female) were captured from the temple towers of Mayiladuthurai (11 0 06' Nand 790

49' E) Tamilnadu, India. They were brought 'to the aviary and kept in individual cages. The body weight of the experimental owls ranged from 400-455g with a mean weight of 435g. The captive owls were fed with bandicoot rats (B. bengaZensis) ad libitum, during acclimatization period of 15 days. , The secondary poisoning study was undertaken when the captive owl's intake became apparently normal and regular l9

.

The secondary poisoning of difethialone to the owl was evaluated as per Newton et aZ19

• Briefly, orally dosed adult bandicoot rats (weighing138±23.0g) were fed to the owls in three phases i.e., phase leone rat/owl once only), phase 2 (one rat/owl/day for three days) and phase 3 (one rat/owl/day for six days). One day before commencing the feeding trail, the bandicoot rats were orally administered with LDso dose of difethialone (0.3 mg/kg to male rat and 0.45mg/kg to female rat20

). During phase 1, poisoned rat fed owls were keenly observed for changes in their behaviour and external bleeding and mortality if any were noted until they recoverd from the poison effect. During remaining days of phase 1 the owls were fed with normal bandicoot rats. Those which survived in phase 1 experiments were taken into next phase of experiments (phase 2). After treatment, the treated owl fed with normal bandicoot rats and their behavioral changes were noted until they recovered.

1014 INDIAN J EXP BIOL, OCTOBER 2004

Any owl that survived in the phase 1 and phase 2 were later fed for six days on dosed rats (phase 3). After treatment, if any owl survived, it was fed with normal rats and the behavioural changes were observed up to 75 days. The findings were used mainly to assess the non-target mortality due to secondary poisoning of difethialone. If yes, how many dosed rats/how much amount of poison produce mortality to the owls?

Statistical analysis-Analysis of variances (one way ANOY A) and multiple comparisons test, 'Student-Newman-Keuls test' (SNK) were used to work out the difference in the poison intake of Barn owl in different treatments using MINI TAB Computer Software package. Statistical inferences were made by following Sokal and Rholf21.

Toxicity trials-In the present study, owls ate only the anterior parts of the poisoned rat (head, thorax, fore legs and abdomen). The intake of difethialone by owls was lowest during phase 1 (0.05 ± 0.003 mg/kg) and highest during phase 2 (0.16 ± 0.042 mg/kg) however, it declined during phase 3 (0.13 ± 0.019 mg/kg) (Fig. 1). The experimental owls died after receiving a cumulative dose of 0.274mg/kg (owl 1), O.365mg/kg (owl 2) and 0.39Img/kg (owl 3) (Fig. 1). The intake of difethialone among the 3 phases was significantly different (ANOY A F2.6=12.29; P<0.05). Further analysis of data (SNK test) revealed that the phase 1 was completely different from other phases whereas difference between phase 2 and phase 3 was not statistically significant (Fig. 1).

Behavioural response-After feeding a treated rat in phase 1, the owls did not show any symptom of poisoning, however they were sluggish (always sleeping and no respond to handling) up to the 20th

0.45

0.4

0.35

0.3 CI 0.25 "" e;,

0.2 E 0.15

0.1

0.05

0

~Barnowl1 c::::JiBarn owl 3 ~Barn owl 2

Phase 1

E1rn!l Barn owl 2 -.-Sarn owl 1 ... Barn owl 3

Phase 2 Phase 3

Fig. i-Amounts of difethialone consumed by the Barn owls in different phases. [Vertical bar indicates the consumption of difethialone and line graph indicates the cumulative amount of poison consumed by the Barn owls. In the outset, the horizontal line connects the two similar means (SNK test)]

day. During 20th day they were found to be normal, their feeding, flying and other regular activities were also normal. Then the phase 2 started on 21 st day. In this phase, the owls were fed with a poisoned rat per day for 3 days from day 21 to day 23. Barn owl 1 did not take poisoned rat on day 23; on day 24 and 25, bleeding on the left foot was observed in this owl. Another owl (owl 2) failed to respond to handling on the 25th day. The owl 3 did not show any noticeable symptom except dullness. Then all the 3 experiment owls were sluggish up to 50th day. During 50th day they were found to be normal, their feeding, flying and other regular activities were also normal. Then the phase 3 started on 51 st day, where all the three owls were fed with 1 poisoned rat per day. All the three owls died before completion treatment period (1 rat/owl/day for 6days) of the phase 3 except owl 3 which died on 56th day. The owl 1 ate on the poisoned rat only on day 51, showed dullness on day 52 and eventually died on the next day due to internal haemorrhage. The owl 2 which consumed poisoned rats on the day 51, 52 and 53 during phase 3, stopped feeding on day 54 and died on the 55th day, because of hamorrhage on the beak and breast from day 52 onwards. The owl 3 which consumed poisoned rats continuously from day 51 to 54, also stopped feeding on day 55 and died on the 56th day. The post mortem examination showed the internal haemorrhages in the dead owl.

The environmental risk of use of rodenticide depends not only on the toxicity of the rodenticide but also on its exposure to the non-target animals2 and as such a vital step in the development of any rodenticide is to assess whether the product has only unacceptable effects on non-target vertebrates exposed either as bait or poisoned rodents. Kaukienen22 and Colvin et aP3. have explicitly discussed hazards to wildlife assoiciated with anticoagulant rodenticides. In the present study, the owls ate only the anterior parts of the poisoned rats (head, thorax, fore legs and abdomen) leaving out the remaining parts. Similarly, Gray et aP4 also reported that the Barn owls when fed with rodenitcide dosed mice did not swallow the whole mice but dismembered them prior to consumption and rejected up to 40% of the body of mice poisoned with brodifacoum and up t070% of the body of mice poisoned with flocomafen and difenacoum. In the present study, the owls died after consuming cumulative dose of difethialone below O,4mglkg of

NOTES 1015

body weight. In contrast, Gray et ap4. observed that the owls survived a dose of at least 0.13 mg/kg body weight per day over 15 . days (equivalent to a cumulative dose of 1.9 mg/kg body weight); however, two flocoumafen fed owls died after consuming cumulative doses of 2.2 and 2.8 mg/kg. Similarly, two brodifacom fed owls survived 3.2 and 3.3 mglkg but one owl fed with 5.4mg/kg died. On the contrary, one owl injesting 5.5mglkg difenacoum rodenticide survived and the one injesting 3.7mglkg of poision died. Newton et aP5. found that a dose of 0.93mg/kg of flocoumafen (fed via flocoumafen dosed mice) to cause mortality in Barn owls. Thus, comparison of the results obtained in the present study for difethialone with others showed that its toxic dose is far less than the lethal doses reported earlier for other anticoagulants viz., brodifacom, difenacoum and flocoumafen. Thus, it may be inferred that difethialone could cause more secondary toxicity to Barn owls than the other anticoagulants of same generation.

However, such vanatIons observed among these laboratory studies involved a highly controlled situation and may relate, in part, to artificial test conditions22 and diet changes26

. 27. Kaukienen22 stated that many additional laboratory testing variables and limitations make most existing lab-derived secondary toxicity data and proposed testing protocols of limited utility in the sense of extrapolating to a field hazard sitution. Importantly, rodenticide exposure is actively and rigidly controlled by the experimenter in the laboratory rather than being a passive encounter during normal feeding and habitat use, as occurs in the field. Because specific use patterns and formulation of bait in relation to foraging behaviour of the non-target animals cannot be taken easily into direct account, dose levels administered in the laboratory become tests of toxicity rather than an absolute determination of hazard23

.

According to Colvin et aP3. laboratory studies can generate important base-line information for determining whether a field study should be initiated. Since in the present study the difethialone was found to be comparatively more toxic to Bam owls than the toxicity values reported for other rodentcides, a field study is recommended to fully understand its secondary toxicity hazard to the owls. Such a field evaluation may be in lines with those of Hegdal and Blaskiewicz28

, Harrison6, Gray et ap4. and Eadsforth

et af

Thanks are due to Dr. K.Thiyagesan and Dr. R. Nagarajan, A VC College for suggestions, to UGC, New Delhi for financial assistance and to MIs. AgrEvo, Bombay for rodenticide difethialone.

References I Wagle N G, Bromadiolone, a second-generation anticoagulant

rodenticide, Pesticides, 20 (1987) 30. 2 Eadsforth C V, Gray A & Harrison EG, Monitoring the

exposure of Barn owl to second-generation rodenticide in southern Eire, Pestic Sci, 47 (1996) 225.

3 Johnson R A & Scott R M, Flocoumafen, a new second generation anticoagulant rodenticide, Proc 1" British pest cant conf(Guernsey) 29 May - I June (1986).

4 Mikkola H, Owls of Europe (Pitman Press, Bath) 1983. 5 Eadsforth C V, Dutton A J, Harrison E G & Vaughan J A, A

Barn owl feeding study with ct4C] Flocoumafen - dosed mice: Validation of a non-invasive method of monitoring exposure of Barn owls to anticoagulant rodenticide in their prey, Pestic Sci, 32 (1991) 105.

6 Harrison E G, Eadsforth C V & Vaughan J A, A non-invasive approach for monitoring the exposure of Barn owls to rodenticides, Crop Prot Conf Pest and Disease, 8C-1 (1990) 951.

7 Bunn D S, Warburton A B & Wilson R D S, The Bam owl (Calton Payser) 1982.

8 Duckett J E, Barn owls (Tyto alba) and the second-generation rat-baits utilized in oil palm plantations in Peninsular Malaysia, Plwlter Kuala Lumpur, 60 (1984) 3.

9 Shawyer C R, The Bam owl in the British Isles: Its past. present andfuture (Hawk Trust, London) 1987.

10 Marchant J H, Hudson R, Carter S P & Whittington P, Population trends in British breeding birds (British Trust for Ornithology, Tring) 1990.

II Neelanarayanan P, Nagarajan R & Kanakasabai R, The common Barn owl, Tyto alba: A potential predator of rodent pests, Pestology, 19 (1995) 22.

12 Pukazhenthi K, Socia economic status of rodent management with reference to rice productivity in the adopted villages (PEKAK) of Allballathapuram Vakaiyara Charities, M.Sc Thesis A V C College, MannampandaL

13 Arora K K, Lal J, Kumar V, Ram B & Lal S, Evaluation of difethialone (LM-22 19), a new anticoagulant rodenticide against house rat, Rattus rattus, Rodent Newslett, 16 (1992) 10.

14 Saxena Y & Saxena K, Toxicity of difethialone (LM-2219) against Meriones hurrianae under no-choice feeding test, J BombayNat Hist Soc, 90 (1994) 448.

15 Saravanan K & Kanakasabai R, Evaluation of 0.0025% difethialone against Bandicota bengalensis and Mus booduga, Rodent Newslett, 20 (1996) 6.

16 Kanakasabai R & Saravanan K, Field evaluation of anticoagulant rodenticides bromadiolone and difethialone in sugarcane fields of Cauvery Delta, Indian J Exp Bioi, 37 (1996) 56.

17 Dubey 0 P, Thakur G S & Tiwari S K, Evaluation of bio­efficacy and acceptability of two rodenticide against field rodents, Rodent Newslett, 24 (2000) 10.

18 Saravanan K, Kanakasabai R & Thiyagesan K, Field evaluation of difethialone a new second generation ·

1016 INDIAN J EXP BIOL, OCTOBER 2004

anticoagulant rodentcide in the rice fields, Indian J Exp Bioi, 41 (2003) 655.

19 Newton I, Wyllie I & Freestone P, Rodenticides in British Barn owls, Environ Pollution, 68 (1990) 101.

20 Saravanan K, Evaluation of Toxicity and field efficacy of the second generation anticoagulant rodenticide, difethialone against selected rodent species and its toxicity to the Bam owl, Ph.D Thesis, Bharathidasan University, Tiruchirapalli (200 1).

21 Sokal R H & Rohlf F J, Biometry (W H Freeman and Company, Newyork), 1981.

22 Kaukeinen D E, A review of the secondary poisoning hazard potential to wildlife from the use of anticoagulant rodenticides. Proc ](jh vertebrate pest conf (California Vertebrate Pest Conunittee, Sacramento) 1982, 151.

23 Colvin B A, Hegdal P L, & Jackson W B, Review of non­target hazards associated with rodenticide use in the USA.

OEPPIEPPO Bull, 18 (1988) 301. 24 Gray A, Eadsforth C V & Dutton A J, The toxicity of three

second-generation rodenticides to Barn owls, Pest Sci, 42 (1994) 179.

25 Newton I, Wyllie I, Gray A & Eadsforth C V, The toxicity of the rodenticide, Flocoumafen to Bam owls and its elimination via pellets, Pest Sci, 41 (1994) 181.

26 Colvin H W JR & Wang W L, Toxic effects of warfarin in rats fed different diets. Toxicol Appl Pharmacol, 28 (1974) 337.

27 Oliver A J & Wheeler S H, The toxicity of the anticoagulant pindone to the Europeian rabbit, Oryctotagus cuniculus and the sheep, Ovis aries, Aust Wildl Res, 5 (1978) 135.

28 Hedgal P L & Blaskiewich R W, Evaluation of the potential hazard to Barn owls of talon (brodifacoum bait) used to control rats and house mice, Environmental Toxicol Chemistry, 3 (1984) 167" ..