Food habits and prey spectrum of Spotted Owlet (Athene brama) in Madurai District, Tamil Nadu, southern India

Introduction

Owls play an important role in the maintenance of a natural balance since they are at the apex of trophic levels in terrestrial and aquatic ecosystems (Sergio et al., 2008). Owls are known for their important role in bio-control of pests (Lenton, 1983; Kumar, 1985; Santhanakrishnan, 1987, 1995; Naranthiran, 1989; Neelanarayanan et al., 1994, 1995; Pande and Dahanukar, 2011a, 2011b). Among the various species of owls found in India, the Spotted Owlet (Athene brama Temminck, 1821) is the most common small-sized owl in southern India (Ali and Ripley, 1983). The Spotted Owlet is a generalist predator that feeds on diverse prey such as rodents, small birds, reptiles, amphibians and invertebrates such as insects and annelids (Jain and Advani, 1984; Kumar, 1985; Jadhav and Parasharya, 2003; Pande et al., 2004, 2007). Previous studies on the prey of Spotted Owlet have been reported from northern and western India. We discuss here the food and prey spectrum of the Spotted Owlet in Madurai District, Tamil Nadu, southern India.

Study area

Our study was carried out in Madurai District (9°30′N, 77°28′E), Tamil Nadu, southern India between 2007 and 2009. Paddy is the predominantly cultivated crop in the study area; other crops such as sugarcane, banana, jasmine, betlevine, groundnut and sorghum are also cultivated in different regions of the study area. The mean monthly maximum temperature during the study period is 33.6℃ (range 29.1–36.9℃) and the mean monthly minimum temperature 22.8℃ (range 19.7–25.1℃). The study area receives rainfall during October and December with an annual average of 850 mm.

Methods

During the study period, we observed the food habits of the Spotted Owlets by collecting and analyzing their regurgitated pellets from their roosting and nesting sites. Spotted Owlet pellets were collected fortnightly in six different roosting/nesting sites. Fresh pellets were collected separately during each visit and packed in polythene bags along with tags indicating the site, name and date of collection before being brought to the laboratory. Pellets were kept at 70℃ in a hot air oven for 24 hours to kill any associated invertebrates. The length and width of the pellets were measured by using a Vernier caliper (to nearest mm) and the weight was measured with a digital balance with an accuracy of 1 mg. Pellets were analyzed following the method of Schueler (1972) and Yalden (2003).

Mammalian prey items were identified up to species level by comparing their bony remains (e.g., skulls, mandibles) with museum specimens collected from the same study area. Reptiles were identified by their skulls and mandibles (Naranthiran, 1989). Invertebrate prey items were identified up to order level on the basis of undigested anatomical pieces such heads, mandibles, wings, legs, stings and body rings (Naranthiran, 1989; Yalden, 2003; Asokan et al., 2009). Data are presented as mean ± SD.

Results

Pellets

The fresh pellets of owls were compact and dark in color because they contained masses of undigested material, mostly insects; in contrast, the old pellets were pale in color and held loosely. Intact pellets were classified into three sizes viz., large, medium and small (Fig. 1) and measured 26.3 ± 0.29 mm in length (n = 4181; range 18.0–46.0 mm), 13.8 ± 0.16 mm in width (n = 4181; range 10.0–26.0 mm) and weighed 0.50 ± 0.16 g (n = 275; range 0.10–1.74 g).

Figure  1.  Various shapes and sizes of Spotted Owlet pellets recorded in the study area

DownLoad: Full-Size Img PowerPoint

Prey composition

In all pellets, insects representing the order Coleoptera were predominant and represented in 91.3% of the pellets, followed by Orthoptera (80.8%), Hemiptera (27.0%), Diptera (14.8%) and Lepidoptera (13.3%). Among vertebrates, reptilian remains were found only in 27.2%, followed by Mus spp. (15.7%) (Table 1).

Table  1.  Comparative statistics for different prey items found in pellets of the Spotted Owlet (n = 4181) in the study area during 2007–2009

Prey items	Frequency of occurrence of prey items	Percent frequency of occurrence of prey items (%)	Range	Sum
Invertebrates
Coleoptera	3821	91.3	1–14	16858
Orthoptera	3377	80.8	1–16	13356
Hemiptera	1125	27.0	1–6	1396
Diptera	618	14.8	1–4	704
Hymenoptera	607	14.5	1–5	700
Lepidoptera	560	13.3	1–3	618
Arachnida (Scorpions)	438	10.4	1–2	443
Myriapoda (Millipedes)	25	0.6	1–5	67
Vertebrates
Reptiles	1139	27.2	1–2	1345
Bats	14	0.3	1–2	15
Mus spp.	656	15.7	1–2	678
Rattus rattus	193	4.7	1–2	201
Tatera indica	53	1.2	1–2	54
Bandicota bengalensis	47	1.2	1–2	50
Suncus murinus	154	3.7	1–2	157

 | Show Table

DownLoad: CSV

A total of 40278 individual prey items were obtained from 4181 pellets in the study area between 2007 and 2009. The number of prey items per pellet ranged from 1 to 31 with an overall mean of 9.6 ± 3.03. Invertebrates were the most common prey, representing 84.8% of the total diet, followed by vertebrates (6.2%). Among invertebrates, insects accounted for 83.5% of all individual prey (Table 2) with Coleoptera and Orthoptera species being the most frequent items (41.9% and 33.2%, respectively).

Table  2.  Overall frequency and proportions of various prey items in the pellets of Spotted Owlets during 2007–2009 (n = 4181).

Prey species	Frequency of occurrence	Percentage of occurrence (%)
Invertebrates
Class: Insecta
Order: Coleoptera	16858	41.9
Order: Orthoptera	13356	33.2
Order: Hemiptera	1396	3.5
Order: Diptera	704	1.8
Order: Hymenoptera	700	1.7
Order: Lepidoptera	618	1.5
Class: Arachnida
Order: Scorpionida	443	1.1
Class: Myriapoda
Order: Diplopoda	67	0.2
Vertebrates
Class: Reptilia	1345	3.3
Class: Mammalia
Order: Micro Chiroptera	15	0.04
Order: Rodentia
Mus spp.	678	1.7
Rattus rattus	201	0.5
Tatera indica	54	0.1
Bandicota bengalensis	50	0.1
Order: Insectivora
Suncus murinus	157	0.4
Unidentified prey items	3636	9.0
Total	40278	100.0

 | Show Table

DownLoad: CSV

Spotted Owlets consume a narrow spectrum of vertebrate prey, consisting only of reptiles and mammals in their diet (3.3% and 2.8%, respectively), although mammalian prey consisted of five rodent species and an unidentified bat (Table 2).

Temporal variations in prey

Seasonal variation During the three years we studied the diet of the Spotted Owlets, a total of 9018 prey items were identified from post-monsoon seasons, 10957 during summers, 13092 from pre-monsoon seasons and 7211 during the monsoons. Invertebrates were the most common prey during all seasons which were at their maximum in the post-monsoon seasons. Among invertebrates, insect formed always the largest amount of prey consumed in all seasons, accounting for 83.4%. Among insects, Coleoptera species were the most commonly consumed prey and in similar proportions during all seasons. Reptiles and mammals constituted over 4% of all individual prey during all seasons (Table 3).

Table  3.  Seasonal variations in the frequency and proportion of various prey items in the pellets of the Spotted Owlet during 2007–2009

Prey species	Post-monsoon (Jan–Mar)			Summer (Apr–Jun)			Pre-monsoon (Jul–Sep)			Monsoon (Oct–Nov)
	n	%		n	%		n	%		n	%
Invertebrates
Class: Insecta
Order: Coleoptera	3881	43.0		4559	41.6		5386	41.1		3032	42.0
Order: Orthoptera	2960	32.8		571	32.6		4362	33.3		2463	34.1
Order: Hemiptera	287	3.2		408	3.7		466	3.6		235	3.3
Order: Diptera	161	1.8		216	2.0		252	1.9		75	1.0
Order: Hymenoptera	132	1.5		205	1.9		266	2.0		97	1.4
Order: Lepidoptera	135	1.5		189	1.7		203	1.5		91	1.3
Class: Arachnida
Order: Scorpionida	111	1.2		124	1.1		151	1.2		57	0.8
Class: Myriapoda
Order: Diplopoda	67	0.7		−	−		−	−		−	−
Vertebrates
Class: Reptilia	306	3.4		377	3.4		442	3.4		220	3.1
Class: Mammalia
Order: Micro Chiroptera	6	0.1		6	0.1		3	0.02		−	−
Order: Rodentia
Mus spp.	157	1.7		205	1.9		212	1.6		104	1.4
Rattus rattus	53	0.6		60	0.6		61	0.5		27	0.4
Tatera indica	5	0.1		29	0.3		18	0.1		2	0.03
Bandicota bengalensis	9	0.1		16	0.2		20	0.2		5	0.05
Order: Insectivora
Suncus murinus	26	0.3		45	0.4		59	0.5		27	0.4
Unidentified prey items	722	8.0		947	8.5		1191	9.1		776	10.8
Total prey items	9018			10957			13092			7211
Number of pellets	940			1147			1319			775
Mean prey per pellet	9.6 ± 2.86 (Range: 2–22)			9.6 ± 3.02 (Range: 1–22)			9.9 ± 3.07 (Range: 4–31)			9.3 ± 3.16 (Range: 4–21)

 | Show Table

DownLoad: CSV

Yearly variation During each of the three years invertebrates were the dominant prey items in the diet of Spotted Owlets among which insects were the most numerous (Table 4). Among insects, Coleoptera species constituted virtually a stable proportion of prey in every year.

Table  4.  Yearly variations in the frequency and proportion of various prey items in the pellets of the Spotted Owlet during 2007–2009

Prey species	2007			2008			2009
	n	%		n	%		N	%
Invertebrates
Class: Insecta
Order: Coleoptera	1868	41.6		7991	42.4		6999	41.3
Order: Orthoptera	1397	31.1		6412	34.0		5547	32.7
Order: Hemiptera	143	3.2		605	3.2		648	3.8
Order: Diptera	54	1.2		286	1.5		364	2.2
Order: Hymenoptera	35	0.8		283	1.5		382	2.3
Order: Lepidoptera	45	1.0		259	1.4		314	1.9
Class: Arachnida
Order: Scorpionida	23	0.5		190	1.0		230	1.4
Class: Myriapoda
Order: Diplopoda	−	−		−	−		67	0.4
Vertebrates
Class: Reptilia	149	3.3		640	3.4		556	3.3
Class: Mammalia
Order: Micro Chiroptera	−	−		−	−		15	0.1
Order: Rodentia
Mus spp.	54	1.2		357	1.9		267	1.6
Rattus rattus	16	0.4		89	0.5		96	0.6
Tatera indica	−	−		24	0.1		30	0.2
Bandicota bengalensis	−	−		17	0.1		33	0.2
Order: Insectivora
Suncus murinus	38	0.9		51	0.3		68	0.4
Unidentified prey items	665	14.8		1638	8.7		1333	7.9
Total prey items	4487			18842			16949
Number of pellets	590			1967			1624
Mean prey per pellet	7.6 ± 2.03 (Range: 3–20)			9.6 ± 3.19 (Range: 3–31)			10.4 ± 2.78 (Range: 1–22)

 | Show Table

DownLoad: CSV

Mammalian prey size

Spotted Owlets consumed prey species with a wide range of weight classes, ranging from 1 g (insects) to > 80 g (mammals). The weight of the mammalian prey items captured by the Spotted Owlet ranged from 5 g (Mus spp.) to 84 g (Rattus rattus). Among the various prey weight classes, the Spotted Owlet consumed mammalian prey mostly in the 1–20 g (68.1%) weight class, followed by the 20–40 g (19.8%) class. The other prey weight classes of > 40 g accounted for 12.11% (Table 5).

Table  5.  Relative occurrence of various mammalian weight classes in the diet of Spotted Owlets during 2007–2009

Weight class (g)	Mus spp.			R. rattus			T. indica			B. bengalensis			S. murinus			Total
	n	%		n	%		n	%		n	%		n	%		n	%
1–20	678	100		43	21.3		20	37.0		4	8.0		32	20.3		777	68.1
20–40	−	−		67	33.3		29	53.7		8	16.0		121	77.1		225	19.8
40–60	−	−		74	36.9		4	7.4		33	66.0		4	2.6		115	10.1
60–80	−	−		13	6.5		1	1.9		5	10.0		−	−		19	1.7
80–100	−	−		4	2.0		−	−		−	−		−	−		4	0.3
Total	678			201			54			50			157			1140

 | Show Table

DownLoad: CSV

Discussion

In Pakistan, Beg et al. (1990) classified the regurgitated pellets into three size levels: large, medium and small. We followed the same categorization in pellet size in the present study. The size and shape of the pellets usually depend upon the size and the quantity of undigested materials found from the prey. The average measurements of the pellet sizes reported in other studies (Pande et al., 2004; Tariq et al., 2003) are different from our findings, which might be due to more insects per pellet.

The mean number of prey items per pellet in our study was 9.6 ± 3.03 (range: 1–31). Naranthiran (1989) once reported a mean number of 11.6 prey items in Tamil Nadu and Pande et al. (2007) registered a mean number of 6.9 prey items in Maharashtra. In contrast, Mahmood-ul-Hassan (2007) reported a mean number of only 1.6 prey items at Pakistan. Variations in the number of prey items per pellet is usually affected by a number factors such as size of the prey available, surface activity of prey, how hungry the owls are, the nutritional value and biomass of the prey, prey selection or prey diversity in an area (Santhanakrishnan, 1995). If the prey size is large (> 20 g) the number of prey items per pellet may decrease; inversely, it may increase when the prey is very small (< 1 g insects).

Irrespective of the year and season, invertebrates were the most common prey in the diet of Spotted Owlets. Our results were similar to those documented for the Spotted Owlet in India (Jain and Advani, 1984; Kumar, 1985; Naranthiran, 1989; Jadhav and Parasharya, 2003; Pande et al., 2004, 2007) and Pakistan (Beg et al., 1990; Shah et al., 2004; Mahmood-ul-Hassan et al., 2007).

Among insect preys, Coleoptera were the species consumed in the largest amounts by the Spotted Owlet in our study area. Several previous studies also identified Coleoptera species as one of the most important food sources for this owl species (Jain and Advani, 1984; Kumar, 1985; Jadhav and Parasharya, 2003; Pande et al., 2004). Although we recorded a considerable amount of appendages, elytra, mandibles and heads of various species of beetles in the pellets, we could only identify this up to the order level due to the paucity of proper methods and guides for identification. Tariq et al. (2003), Shah et al. (2004) and Mahmood-ul-Hassan et al. (2007) reported that Coleoptera are also the most common insects consumed by Spotted Owlets in Pakistan. After Coleoptera, Orthoptera species also formed important insect prey. Kumar (1985) recorded that Orthoptera species accounted for 72% of all individual prey taken by Spotted Owlets and Naranthiran (1989) 67%. A number of other studies have also recorded the occurrence of Orthoptera species in the diet of this owl (Ali and Ripley, 1983; Jain and Advani, 1984; Jadhav and Parasharya, 2003; Pande et al., 2004). In our study area, Coleoptera and Orthoptera species were frequently recorded in agricultural fields and most often attracted to sources of light during night hours. On many occasions Spotted Owlets were observed on electric power lines feeding on these insects which are usually attracted by light. Those insects that were taken in negligent proportions possibly constituted a supplementary prey resource or may have been captured by chance or availability. In Madurai, Spotted Owlets also consumed scorpions. Similarly, Kumar (1985) and Pande et al.(2004, 2007) found scorpions in the diet of this owl species.

Consumption of reptiles by Spotted Owlets in Madurai was comparable to that documented for the species in India (Jadhav and Parasharya, 2003; Pande et al., 2007) and Pakistan (Shah et al., 2004; Mahmood-ul-Hassan et al., 2007). Reptilian prey remains have also been commonly recorded in the food habits of other owl species in India (Verzhutskii and Ramanujam, 2002; Srinivasulu and Srinivasulu, 2007).

Composition of small mammal prey in the diet of Spotted Owlets in Madurai was similar to results obtained by other authors in India (Jain and Advani, 1984; Kumar, 1985; Naranthiran, 1989; Pande et al., 2004). Recent studies at Maharashtra, India, detected 11 species of rodents in the diet of the Spotted Owlet (Pande et al., 2007). Mahmood-ul-Hassan et al. (2007) found five species of rodents, with Mus spp. accounting for > 20% of all prey items in the diet of the Spotted Owlet in Pakistan. The frequent occurrence of mice, rats and shrews in the pellets of the Spotted Owlet suggest that the owlets hunt around human settlements as well as in agricultural areas.

In Madurai, we found that size of the mammalian prey consumed by Spotted Owlets ranged from 5 g (Mus spp.) to 84 g (Rattus rattus), but over 68% of the prey were in the 0–20 g weight class. Mahmood-ul-Hassan et al. (2007) reported that the average weight of mammalian prey caught by Spotted Owlets in Central Punjab, Pakistan, varied between 5 g (Suncus etruscus) and 131 g (Tatera indica). Pande et al. (2007) reported that the approximate mean biomass of mammalian prey in the diet of the Spotted Owlet in Maharashtra, India, ranged from 2 g (Suncus etruscus) to 75 g (Golunda ellioti). From the present study it is evident that the Spotted Owlet forages on a wide variety of prey species, available in and around human habitations and agricultural areas. The presence of bats in the diet of the Spotted Owlet indicates that they perform aerial hunting too. The food habits of the Spotted Owlet show a stereotypic pattern in the consumption of various prey species among seasons and years, suggesting that they forage opportunistically. Further studies on the prey availability estimation of various species in the habitat of this owl may yield more information on prey selection.

Acknowledgements

As authors we are thankful to the Ministry of Environment and Forests, Government of India, for providing financial support for this study. We are grateful to the Principal and Management of Saraswathi Narayanan College (Autonomous), Madurai, for facilities and encouragement. We are thankful to Mr. P. Muthukumar, Field Assistant, for accompanying us during field trips.