What Do We Know about the Diet of Ecuadorian Owls?

Abstract

Ecuador territory barely surpasses 28 million hectares, but it is home to 29 owl species, which represent 62% of all owl species in South America. Knowledge of the trophic ecology of owls is fundamental for understanding how they correlate with their environment, which organisms they prey upon, and to which extent they are beneficial for humans’ health. Although publications in this field have grown in Ecuador in recent years, background information is still deficient. At present, the diet of a handful of species has been studied in this Andean country, and for a few other species, there is only anecdotal information, such as stomach contents of specimens, held in scientific collections. In this chapter, we review knowledge about the diet of owl species occurring in Ecuador and provide guidelines for the study of pellets with the aim of motivating more research in this field.

1. Introduction

Nocturnal birds of prey birds have long been considered as a “unit” in several classifications of animals [1, 2]. Currently, they are classified in the order Strigiformes, within a larger group called the “African landbird radiation” that includes the orders Cathartiformes, Accipitriformes, Trogoniformes, Coraciiformes, Piciformes, among others [3]. The Strigiformes are difficult to study because they occur in low densities, have generally elusive behaviors, most are strictly nocturnal, and usually remained overlooked [4]. Although research on Strigiformes biology has intensified over the last few decades [2], many owl species remain little studied.

Knowledge about the feeding ecology of Strigiformes, including which organisms are preyed upon them, is a key for understanding their role within a given ecosystem, and even elucidating whether they can be beneficial for human health. However, witnessing owl predation events in the wild is unusual, so analyses of owl pellets become the most effective method for studying their diets. Owls usually swallow their prey whole or in large pieces, and then regurgitate a pellet containing indigestible matter, such as bones, fur, feathers, and other keratinous material, about once a day [5]. Owl pellets are also an efficient alternative for measuring small mammal community composition [6].

Ecuador is home to 29 out of 45 South American species of Strigiformes [7]. For the majority of owls occurring in Ecuador, scarce information about their natural history exists, including their feeding ecology [8]. As there are few reviews of the diet of Neotropical owls at country scales [9, 10], in this chapter, we present a revision of information on the diet of owls in Ecuador. Further, we present some guidelines for the study of owls’ diets and highlight topics that could be investigated. Our aim is to promote further scientific research about the feeding ecology of nocturnal birds of prey.

2. Previous knowledge

Mammals, birds, reptiles, amphibians, and invertebrates are roughly the usual prey for owls, but what is the preferred prey of each species? There is published information on nine out of the 29 species of owls occurring in Ecuador; the remaining 20 species have only anecdotal data, whereas for two there is virtually no information on their diet in Ecuador. Given that there are few peer-reviewed publications about the diet of Ecuadorian owls, in this section, we also include gray literature, such as conference papers or thesis, and unpublished information compiled by the authors in the field and in a revision of museum specimen labels. The level of taxonomic identification of the prey is variable, according to secondary information. We have tried to identify our own observations to the highest taxonomic level possible.

2.1 Tyto furcata

T. f. contempta: There are only three specimens (MECN 6833, 8773, 8678) of this common and widespread taxon with stomach content information. They contained remains of Coleoptera and rodents. Stomach content of MECN 6992 mentions herbs as the only item, so it cannot be considered secondary content (i.e., stomach contents of a prey); it could have been accidentally ingested when hunting.

There are two studies of its diet using pellets, but from a mammalogy approach, so non-mammal preys were overlooked. These studies underline the high consumption of rodents [11, 12].

This is the best-studied species in Ecuador, most studies being based on pellets analyses, and covering as varied habitats as cities [13, 14], rural areas, or agricultural fields in the Pacific lowlands [15, 16, 17] and Andean valleys [18]. However, there is no long-term research on its diet or a broader study aiming to understand feeding preferences in relation to prey abundance and availability.

The predominance of rodents in the diet of T. furcata is consistent with studies in other countries [18 and cites therein]. However, this species is also opportunistic, preying upon other kinds of prey, including bats [14] or high number of birds in agricultural and open habitats [18]. Six pellet studies showed the following quantitative data:

In Cuenca, Azuay province, n = 245: 249 introduced rodents, 95 native rodents, 7 birds, and 93 Coleoptera items [13]. In Pallatanga, Chimborazo province, n = 61: 25 introduced rodents (Mus musculus and Rattus sp.), 132 native rodents, 2 Sylvilagus andinus, 3 birds, and 2 reptiles. In Calceta, Manabí province, n = 46: 34 introduced rodent (M. musculus), 99 native rodents, 2 Proechimys decumanus, 1 Marmosops sp., and 1 Sylvilagus daulensis [15]. Another study in Cuenca, Azuay province, n = 32: 100 introduced rodents, 29 native rodents, 1 vampire bat Desmodus rotundus, 2 birds, 4 reptiles, and 18 Coleoptera [14]. In Zapotillo, Loja province, n = 65: 130 M. musculusand 42 native rodents [16]. In another sample from Calceta, Manabí province, n = 30: 57 native rodents, 7 bats, and 1 dove [17]. The largest pellet sample studied in Ecuador included 361 pellets and 664 g of pellets debris from San Antonio and Tababela, Pichincha province. This sample included 86 introduced rodents, 803 native rodents, 67 S. andinus, 93 birds, 6 reptiles, and 63 insects [18].

T. f. punctatissima: The Galapagos endemic subspecies is little studied as compared to other Galapagos land birds [19]. The first available information was provided from a sample of 1217 pellets collected in Santa Cruz and Isabela islands [20]. It reports 2230 mammal prey (mostly M. musculus), 81 birds, 10 reptiles, and 2440 invertebrates. A second study reported 90% of rodents, 14% of insects, and less than 1% of birds from a sample of 104 pellets collected on Santa Cruz Island [21, 22]. Details of specific prey found in the latter study will be published elsewhere.

2.2 Megascops albogularis

M. a. albigularis: Stomach contents of three museum specimens (MECN 6150, 7755, 7760) contained remains of a myriapod, also orthoptera, and other insects [23].

There is no other available information on its diet, but one wild pair is being fed raw chicken pieces in Zuro Loma, Pichincha province (Figure 1). The behavioral implications of this artificial feeding are not known, but there are records of carrion consumption by owls, including Megascops species [24]. This event might allow close observations of this owl by birders and nature lovers, which could increase their empathy and appreciation, and promote its conservation. This case deserves further study.

Figure 1.

Megascops albogularis feeding on raw chicken pieces in a private reserve in Pichincha. Photo: Courtesy of Edison Buenaño.

M. a. macabrum: Stomach contents of one museum specimen (MECN 772) had insect remains [23].

2.3 Megascops choliba crucigerus

Stomach contents of one museum specimen (MECN 3994) had insect remains [23]. Another museum specimen (MECN 9633), not included in the cited work, also had insect remains.

2.4 Megascops koepckeae

An unreported number of pellets of this species was only recently reported for Ecuador [25], collected in Loja city, and contained mainly insects and the introduced Mus musculus [26]. There is one record of nestling being provisioned with one scorpion and one frog [D. Pacheco pers. obs.].

2.5 Megascops ingens

M. i. ingens: Stomach contents of five museum specimens (MECN 773, 7288, 7758, 7763, 7773) contained remains of the order Orthoptera (crickets, grasshoppers) and other unidentified insects [23].

M. i. colombianus: One individual mist-netted in Río Guajalito, Pichincha province, carried an opossum Marmosops impavidus on its talons, of which the entire head and forelimbs had already been eaten [27]. There is an additional observation of Carabidae (Coleoptera) remains in an abandoned nest, in Nanegalito, Pichincha province (JF. Freile pers. obs.).

2.6 Megascops petersoni

Stomach contents of six museum specimens (MECN 774, 775, 7752, 7762, 7866, 7867) had remains of the order Orthoptera (crickets, grasshoppers) and other unidentified insects [23].

2.7 Megascops centralis

Stomach contents of three museum specimens (FMNH 372109, MECN 5994, 7062) had remains of an Orthoptera, Coleoptera, other insects, and two centipedes [23]. These authors erroneously reported caterpillar remains of specimen MECN 6361, which is actually Megascops roboratus (see below). Another museum specimen (MECN 9987) had insect remains.

Direct observations in a nest at Loma Alta, Santa Elena province, where recorded five food delivery events to nestlings [28]. These authors also collected three pellets, some pellet debris, and prey remains in the nest. Prey provisioned to nestlings included 55 Tettigoniidae, Acrididae, Coleoptera, Lycosidae, Amblypygi, Anura, and Passeriformes. No quantitative data on each prey are presented. There is an observation of a direct attack on a cicada in Mashpi, Pichincha province (JF. Freile pers. obs.).

2.8 Megascops roraimae napensis

Stomach contents of three museum specimens (MECN 7004, 7636, 7772) had remains of the orders Coleoptera, Orthoptera, other insects, and a bone [23]. MECN 8183 also had remains of insects.

2.9 M. roboratus

M. r. pacificus: Stomach contents of one museum specimen (MECN 771) had insect remains [23]; another specimen (MECN 6301) had caterpillars.

There is no information on the diet of M. r. roboratus.

2.10 Megascops watsonii

Stomach contents of three museum specimens (ANSP 186787, MECN 969, 7764) had remains of spiders, also Orthoptera, and other insects [23].

2.11 Lophostrix cristata

L. c. wedeli: Stomach contents of one museum specimen (MECN 6444) had remains of Orthoptera and other unidentified insects [23].

No information on the diet of L. c. cristata.

2.12 Pulsatrix perspicillata

P. p. perspicillata: One pellet from Cuyabeno, Sucumbíos province, had one lizard Thecadactylus solimoensis [29].

P. p. chapmani: Stomach contents of one museum specimen (QCAZ 4503) had two Iguana juveniles and a moth larva [23].

In a sample of nine pellets collected in Zapotillo, Loja province, 12 mammal preys were found, along with one frog, one reptile, and one invertebrate. The native rodent Rhipidomys leucodactylus was the most important prey in terms of frequency (40%) and in biomass contribution (54%) [30].

2.13 Pulsatrix melanota

Stomach contents of three museum specimens (QCAZ 3508, MECN 6838, 7774) contained only insects of the orders Hemiptera, Mantodea, Orthoptera, and Phasmatodea [31]. Additionally, some pellets of a recently fledged juvenile observed in Tundayme, Zamora Chinchipe province (Figure 2) had Coleoptera remains, mainly (MC. Ríos unpubl.). An adult stayed close to the juvenile, while the observer approached it, and she was even attacked by the adult.

Figure 2.

Pulsatrix melanota recently fledged juvenile and its pellet in the inset, July 2019. Photos: MC. Ríos and courtesy of Luis Gualavisí.

2.14 Bubo virginianus nigrescens

Sylvilagus andinus were the main prey brought to a nest in Cotopaxi volcano, Cotopaxi province [32]. There is an additional observation of an adult preying upon a S. andinus in Antisana, Napo province, and a rat, presumably Rattus sp., in Cañón del Chiche, Pichincha province (JF. Freile pers. obs.).

2.15 Strix virgata

S. v. virgata: Stomach contents of three museum specimens (ANSP 181031, MECN 6991, 8350) contained remains of Coleoptera, other insects, and one reptile [23]. No information from the Amazonian population, whose subspecific identity remains unsolved [33].

2.16 Strix nigrolineata

The only available documentation is a video of an adult preying upon a moth (Sphingidae) in Buenaventura Reserve, El Oro province (https://macaulaylibrary.org/asset/201777541). It has been observed capturing large moths (undetermined families) in light posts at Mindo, Pichincha province, and Los Cedros, Imbabura province (JF. Freile, pers. obs.).

2.17 Strix huhula

There is one unpublished observation of hunting bats in a streetlight in Puyo, Pastaza province (JF. Freile pers. obs.). In addition, a photographic record of one adult preying upon a rat in San Isidro, Napo province (https://macaulaylibrary.org/asset/457375971), pertains to an isolated population whose subspecific identity remains unresolved [34]. There are several additional observations from San Isidro of large Lepidoptera and Coleoptera predation at streetlights, as well as unidentified bats and one unidentified rodent [Holroyd & Trefry unpubl.].

2.18 Strix albitarsis

One small mammal without a skull for identification and four Coleoptera of the genus Megaceras were found in three pellets collected in Yanayacu, Napo province [35]. Stomach contents of four museum specimens (MECN 793, 6927[ex 927], 6135, QCAZ 1544) contained remains of insects in the orders Blattodea and Coleoptera, other unidentified insects, and rodent fur [23].

2.19 Glaucidium nubicola

Stomach contents of one museum specimen had insect remains and one lizard (ANSP 181044 [holotype]) and another specimen had insects (ANSP 180178) [36].

There is an observation of an adult feeding a juvenile with a lizard [37]. There is also one photographic record of an adult preying upon the lizard Andinosaura oculata in Mindo, Pichincha, at 17 h00 [38]. These authors erroneously identified the observed owl as Glaucidium jardinii, which occurs at higher elevations.

One individual ringed in Reserva Las Tangaras, Pichincha province, had one lizard Pholidobolus vertebralis on its talons when mist-netted and when recaptured [39]. Terrestrial lizards apparently represent an important feature of this owl diet (JF. Freile unpubl.).

2.20 G. jardinii

Stomach contents of five museum specimens (LSUMZ 112509, 112,510, MECN 787, 6034, 7868) had remains of a Coleoptera, other insects, one rodent, and one mammal [23].

2.21 Glaucidium parkeri

Stomach contents of one museum specimen (ANSP 185160) had rests of a bird [23].

2.22 Glaucidium griseiceps

No data from Ecuador and its diet elsewhere are also poorly known, but possibly include insects, spiders, and small vertebrates [40].

2.23 Glaucidium brasilianum ucayalae

Stomach contents of four museum specimens (QCAZ 1452, ANSP 186790, FMNH 316441, MECN 783) had Coleoptera and other insects’ remains [23].

2.24 Glaucidium peruanum

Stomach contents of four museum specimens (MECN 3921 [ex 392], 6134, 6302; QCAZ 3658, LSUMZ 77569) contained remains of the orders Coleoptera, Odonata, Orthoptera, and other unidentified insects [23]. Additionally, there is a photographic record of an adult with a Holcosus septemlineatus lizard on its talons, taken in Uzcurrumi, El Oro province (Bravo X., in litt, Figure 3). Another photographic record, taken in Puerto López, Manabí province, involves the geckoo Phyllodactylus reissii [41]. This observation was made at night. There is an additional observation of an adult preying upon a Microlophus occipitalis lizard in Zapotillo, Loja province (JF. Freile pers. obs.).

Figure 3.

Glaucidium peruanum preying upon a lizard Holcosus septemlineatus in El Oro, May 2019, 14 h30. Photo: Courtesy of Xavier Bravo Guerrero.

2.25 Athene cunicularia

A. c. pichinchae: There are only three specimens (MECN 8754, 8755, 8756) of this common and widespread taxon with stomach contents information, which are only insects. There is only one study of its diet, in a sample of 40 pellets from Piedra Labrada, Loja province, was found 84 rodent prey, 1 reptile, 7 frogs, 593 insects, and 187 other invertebrates. Insects were the most important prey in terms of frequency (80%) and rodents in biomass contribution (95%) [42]. In another sample of 368 pellets from Tababela, Pichincha province, was found 13 rodent preys, 2 reptiles, 156 insects, and 25 other invertebrates. Insects were the most important prey in terms of frequency (68%) and rodents in biomass contribution (75%) [42].

A. c. punensis: Stomach contents of two museum specimens (MECN 779, 6303) had remains of Orthoptera [23]. There is also an observation of predation on frog Rhinella marina in Macará, Loja (JF. Freile pers. obs.).

All studies available for this taxon are consistent with insects as the most important prey in frequency and rodents in biomass contribution [16, 43, 44, 45]. The largest pellet sample studied included 300 pellets from Atahualpa, Santa Elena province; it reported 1981 invertebrates, 266 mammals, 10 reptiles, and 3 birds [43]. This work reports two G. peruanum as prey, based on bills in the pellets, but there are no further details. There are no previous reports of intra-guild predation by A. cunicularia, and it remains plausible that the bill could have been misidentified.

Another study from Jambelí, El Oro province, reported 929 insects, 165 other invertebrates, 151 introduced rodents, and 19 birds, in 182 pellets [44]. Further, in 48 pellets collected in Zapotillo, Loja province, 503 insects, 9 frogs (Bufonidae), 9 wolf spiders (Lycosidae), and 5 scorpions were included [16]. Lastly, a sample of 50 pellets from Calceta, Manabí province, included 544 insects and 16 rodents as preys [45].

No information about subspecies A. c. carrikeri, which is apparently spreading along river islands in the Amazon lowlands [33].

2.26 Aegolius harrisii harrisii

There is no diet information for this subspecies. König et al. [40] mention small vertebrates and insects as probable prey.

2.27 Asio clamator clamator

Stomach contents of one museum specimen (QCAZ 1413) from Bahía de Caráquez, Manabí province, had an opossum Marmosa simonsi [23].

A study of 72 pellets and 284.4 g of pellet debris from Atahualpa, Santa Elena province, also included 1 M. simonsi, 351 rodents, 12 birds, 310 reptiles, 3 frogs Ceratophrys stolzmanni, and 468 insects [46]; insects were the most important prey in terms of frequency (41%) and reptiles in biomass contribution (58%). Authors reported seasonal differences in diet with greater consumption of mammals and reptiles during the dry season, and of insects in the wet season.

Another study is in progress in Cuenca, Azuay province, found principally rodents in its pellets (H. Cadena-Ortiz et al. unpubl.). This study is in an unusual locality for the owl, because there are scarce records from Andean valleys and cities [33].

2.28 Asio stygius robustus

Cadena-Ortiz et al. [47] studied 38 pellets, 127 g of pellet debris and seven prey remains from Quito, Pichincha province, and reported 136 birds, 1 bat, and 20 Coleoptera. The dove Zenaida auriculata was the most important prey in terms of frequency (74%) and biomass contribution (91%). There is an additional observation of predation on Z. auriculata in Tumbaco, Pichincha province (JF. Freile pers. obs.).

2.29 Asio flammeus

Asio f. bogotensis: 55 rodent preys, 30 other mammals, 8 birds, 1 reptile, 1 frog, and 72 Coleoptera were found in 52 pellets in three locations of Pichincha province [48]. Mammals were the most important prey in terms of frequency (51%) and biomass contribution (87%). Another study of 163 pellets collected in Antisana, Napo province, included 112 rodent preys, 111 Sylvilagus andinus, and 19 Coleoptera. S. andinus was the most important prey in terms of frequency (46%) and biomass contribution (78%) [49].

A. f. galapagoensis: Only five publications exist on the diet of this Galapagos endemic subspecies. First by de Groot [20], who sampled 213 pellets from six islands (Santa Cruz, Champion, Española, Genovesa, Pitt, and Plaza) and found 58 introduced rodents, 320 birds, and 32 invertebrates. A recent study of 45 pellets reported 47% rodents, 37% birds, and 15% insects [21, 22]. Details of specific prey found in the latter study will be published elsewhere. There is also a report of predation of the Galapagos marine iguana Amblyrhynchus cristatus from Isabela Island [50] and the species is known to prey upon seabird nestlings, including storm-petrels [51].

3. Overview

Degree of knowledge about the diet of owls in Ecuador can be ranked into four categories: null (no information), scarce (less than five events reported), limited (at least five events reported), and moderate (at least two studies in different localities). There is no extensive rank in Ecuador, and it will be an owl with many studies over the long term in various habitats and many variables. We define five events as a minimal sample for statistical tests; an event is a museum skin, a pellet, a photograph, an observation, or a report of an independent predation event (Table 1).

Owl	Prey					Source			Level of knowledge
	Mammals	Birds	Reptile	Amphibians	Invertebrates	Pellets	Museum skin	Predation record
Tyto furcata contempta	1962	106	12		174	840	3		3
Tyto furcata punctatissima	2230	81	10		2440	1217			3
Megascops albogularis albigularis					x		3	1	1
Megascops albogularis macabrum					x		1		1
Megascops choliba crucigerus					x		2		1
Megascops koepckeae koepckeae	x			1	x	x		x	1
Megascops ingens ingens					x		5		2
Megascops ingens colombianus	1				x			2	1
Megascops petersoni					x		6		2
Megascops centralis		x		x	x	3	4	6	2
Megascops roraimae napensis					x		4		1
Megascops roboratus pacificus					x		2		1
Megascops roboratus roboratus									0
Megascops watsonii watsonii					x		3		1
Lophostrix cristata wedeli					x		1		1
Lophostrix cristata cristata									0
Pulsatrix perspicillata perspicillata			1			1			1
Pulsatrix perspicillata chapmani	12		3	1	2	9	1		2
Pulsatrix melanota melanota					x	1	3		1
Bubo virginianus nigrescens	x							x	1
Strix virgata virgata			1		x		3		1
Strix virgata superciliaris									0
Strix nigrolineata					x			x	1
Strix huhula huhula	x				x			x	1
Strix albitarsis	1				4	3	4		2
Glaucidium nubicola			7		x		2	6	2
Glaucidium jardinii	2				x		5		2
Glaucidium parkeri		1					1		1
Glaucidium griseiceps									0
Glaucidium brasilianum ucayalae					x		4		1
Glaucidium peruanum			3		x		4	3	2
Athene cunicularia pichinchae	97		3	7	961	408	3		3
Athene cunicularia punensis	433	22	10	10	4136	580	2		3
Athene cunicularia carrikeri									0
Aegolius harrisii									0
Asio clamator clamator	388	14	310	3	469	17	1		3
Asio stygius robustus	1	137			20	38		1	2
Asio flammeus bogotensis	308	8	1	1	91	215			3
Asio flammeus galapagoensis	58	320	1		32	213		1	3

Table 1.

Subspecies of owls present in Ecuador. The numbers of prey indicate consumed individuals, x when the work is merely qualitative. Knowledge level ranges from 0 for null to 3 for moderate.

In order to roughly illustrate the diet breadth of each owl taxa in Ecuador, we organized overall prey into five groups (mammals, birds, reptiles, amphibians, and invertebrates). We excluded studies with an exclusive mammalogical approach or studies without quantitative data on prey (Table 1).

Although this exercise considers prey at a very coarse level (classes), it allows us to see some trends for each owl taxa. In owls with moderate information, there is consumption of items in each class, even if in low numbers, which reinforces the opportunistic behavior of the owls. Additionally, the level of knowledge is only moderate for seven owls in Ecuador. Although nine owl taxa present limited knowledge, only Pulsatrix perspicillata chapmani, Strix albitarsis, Glaucidium nubicola, and Asio stygius robustus have quantitative data. Then G. nubicola could indicate that it is specialized only in reptiles, particularly in lizards. Nonetheless, there are also unquantified records of insect consumption which might suggest that G. nubicola has a tendency to consume lizards but is not specialized in them. On the other hand, owl taxa with larger samples are similar trends with other works, as has already been suggested for Athene cunicularia specialization in insects [44 and cites therein], T. furcata in rodents [18 and cites therein], and A. stygius robustus in birds [47 and cites therein].

4. How to study owl diets

Documenting prey capture by owls in the wild is exceptional unless a nest is found—although the specific identity of prey provisioned to nestlings cannot always be determined. Therefore, the study of pellets is pivotal for understanding species’ diets given the ease of analyzing them and the number of samples that can be obtained with relatively little field effort, once roosting and feeding sites are located.

Following known procedures in pellet studies [9], we suggest following these steps to maximize data collection: 1) Remain at the site of pellet collection until species identity can be confirmed. Alternatively, camera traps can be set up for species documentation and identification. 2) Collect pellets individually and also all pellet debris. 3) Georeference the collection site and make a description of the area. 4) Air dry each pellet for at least 3 days, then measure its maximum length and width with a caliper and weigh it. 5) Soak the pellets individually in water and disaggregate them up to separate bones and other prey remains. From our experience in Ecuador, only skulls, jaws, beaks, mandibles, and elytra are useful for identification purposes. 6) Compare your voucher specimens directly with museum specimens. 7) Use the presence of unique structures, skulls, and pairs of mandibles or elytra to estimate the number of prey per pellet as the minimum number of individuals (MNI). 8) Calculate the percentage of occurrence as the MNI of each species by the total number of individuals of all species. 9) Calculate the biomass consumption as the mean body mass (in g) of each species multiplied by its MNI.

To calculate dietary niche breadth, we suggest standardized Levin’s index [52], which varies from 0 (narrow trophic niche, maximum prey selectivity) to 1 (wide niche, minimum selectivity). Thus, when the values are less than 0.6, the organism is considered a specialist, since it uses a low number of resources and has a preference for certain foods [53, 54]. To determine owls’ foraging strategy, it is necessary to study potential prey richness and abundance in the study area. Strategies could be opportunistic when it ingests the prey in the same relative abundances of its environment, or selective, when it ingests some or all of the prey in different proportions to those present in the hunting area [54]. Degree of dietary overlap between areas or seasons can be analyzed using Pianka’s dietary niche overlap index or through a Chi-square test (χ²) to check for differences in the diet composition between sites or seasons.

5. Relevance to mammalogy

Owl pellets can be an effective alternative for measuring small mammal community composition over large geographic areas due to the relative ease and low cost of field collections [6]. Since it is a noninvasive indirect tool, it allows the collection of valuable osteological information. In Ecuador, analysis of pellets has allowed the recording of rare and difficult-to-collect mammal species like Ichthyomys hydrobates found in western Ecuador 26 years after the last documented record [15]. Pellet contents have also provided an approximation of the species richness of small mammals in areas with no previous information. For example, we have the first data on presence and abundance of native rodents in previously unstudied Ecuadorian localities in the Andes [49] and western lowlands [15].

Monitoring invasive species (M. musculus, Rattus rattus, R. novergicus) by means of pellets could be a mid- and long-term strategy. They are now known to be agricultural pests because they devastate crops, damage the soil, or eat stored agricultural products [55]. They are also a public health problem because contaminate human food with their excrement [56]. Further, they have a severe impact on several endemic and native species preying on or competing for sources [57]. Rattus has caused the extinction of birds on islands, as well as reptiles, small mammals, amphibians, invertebrates, and plants [58]. They are a latent threat to the human species, due to the number of viruses and bacteria they can transmit in their feces, urine, or by direct contact through bites [58].

6. Conclusions

Specific records of a predation event, whether in a stomach content or in field observation, could indicate preference or opportunism of an individual owl. Records of more prey, such as those obtained by pellets, could indicate local or temporal preferences of a population. The diet of owls is possibly the best-known aspect of their natural history, due in part to analyses of their pellets [40]. To date, we have a broad idea of prey selection by few species in Ecuador, but no idea about predator-prey interactions for any species. For example, we do not have studies of trophic ecology for any species of owl in Ecuador, developed over the long term in various habitats throughout its distribution. These studies analyze parameters, such as prey availability in the environment and the selectivity of the predator [9]. Most information published comes from anecdotal observations or from studies limited temporally and spatially, and we are still documenting the general aspects of natural history and distribution, but not yet assessing patterns and processes [34].

Rescue centers and/or zoos are the potential sources of relevant information that is currently being lost. Many recently captured or rescued owls arrive at these centers, and some might have prey in their stomachs, providing information on diet and digestion times [59], and in this way not only rescue individuals but also contribute to adding nature history information and eventually in real support for the conservation of the species. However, bureaucratic pitfalls and lack of trained personnel in the national environmental authority discourage research, also they do not store complete or useful information about their rescues, many rescued species are misidentified, and often several “rescues” are not actually needed since they are juveniles that recently abandoned their nest and are learning to fly; rescuing them results in taking them away from their parents and habitats.

It is important to continue publishing natural history reports, including, for example, visual or photographic records of specific predation events that can shed light on owls’ capture methods or activity schedules. To date, most publications about Ecuadorian owls pertain to T. furcata, mirroring the situation of this species in other Neotropical countries [9]. More information on pellets comes from dry areas such as the southwestern tropics and the Andean valleys since pellets are better preserved in dry than in humid environments like the Amazonian rainforests or cloud forests along Andean slopes. Dietary information of humid forest owls reported for Ecuador to date corresponds to less than three pellets [29, 35].

An owl species’ diet is often inferred from its bill form and/or knowledge about its congeners. Yet, diets may vary due to factors, such as seasonality, sex, ontogeny, availability of prey, or geography, even in nearby or similar geographical areas, individuals could differ in diet [60]. Therefore, it is important to continue studying and publishing information even about common species like T. furcata and A. cunicularia (Figure 4). On the other hand, since Megascops roboratus and G. nubicola are regional endemics (i.e., their global distribution ranges are mainly confined to Ecuador [34]), studying them in Ecuador is promising as to obtain natural history information.

Figure 4.

Athene cunicularia preying upon a Coleoptera in Tungurahua. Photo: Courtesy of Christiana Fattorelli.

Of 29 species of owls present in Ecuador, there are no diet data in the country for two species (Glaucidium griseiceps and Aegolius harrisii). If we narrow this analysis to the 39 subspecies present, four additional taxa are added to this figure: Megascops roboratus roboratus, Lophostrix cristata cristata, Strix virgata cf. superciliaris, and Athene cunicularia carrikeri. There are only 11 museum specimens with information about stomach contents deposited in Ecuadorian bird collections, all from MECN, that were not studied earlier [23]. Most information in specimen labels, though, is basic and unquantified. Likewise, there are only eight new papers [14, 18, 28, 30, 44, 46, 47, 49] reporting owl species diets since the only state-of-the-art revision by Freile et al. [34].

Acknowledgments

Thanks to Edison Buenaño (www.swordbilledexpeditions.com), Luis Gualavisí, Xavier Bravo Guerrero, and Christiana Fattorelli for sharing photos for this chapter, and to curators of natural history museums for sharing or letting us review information: Cesar Garzón, Museo Ecuatoriano de Ciencias Naturales del Instituto Nacional de Biodiversidad (MECN-INABIO); Santiago Burneo, Pontificia Universidad Católica del Ecuador (QCAZ-PUCE); Edith Montalvo, Escuela Politécnica Nacional (EPN); Leonardo Ordoñez, Universidad Técnica Particular de Loja, Bernarda Vásquez, Universidad del Azuay; and Félix Man-Ging, Universidad de Guayaquil.

Conflict of interest

The authors declare no conflict of interest.