Citizen Science for the Knowledge of Brazilian Birds: Breeding Aspects of the Horned Sungem (Heliactin bilophus) (Aves, Trochilidae) in the Brazilian Cerrado

Introduction

Citizen science projects can substantially increase scientific knowledge regarding bird biology and distribution [1, 3]. In Brazil, investigations based on citizen science data are substantially less numerous than those based on data gathered by professional ornithologists; however, it has been widely recognized that studies based on citizen science data can improve the knowledge and conservation of Brazilian birds [4, 5, 6, 7, 8]. The extraordinary bird species richness found in Brazil [9] is one of the factors that call for the contribution of citizen scientists to better understand patterns and processes concerning its avifauna.

Among this highly diversified avian fauna is the Family Trochilidae that comprises 89 species of hummingbirds in Brazil [9]. They are found in a wide range of habitats, including rainforests, savannas, grasslands, and dry forests [10, 11, 12, 13]. The Horned Sungem Heliactin bilophus (Temminck, 1820) is the only species of this genus [13]. It is widely distributed throughout South America, including an extensive area in Brazil, and more restricted regions in northern and eastern Bolivia, and southern Suriname; in Brazil, its distribution substantially overlaps with the Cerrado, but it also occurs spottily in the Amazon, the Caatinga, and northern Atlantic Forest [14].

The Horned Sungem is one of the smallest hummingbird species found in Brazil [11]. In central Cerrado, it occurs in open vegetation physiognomies, being more common in grasslands than in woodland savannas [11, 15]. Populations can be resident or migratory [16, 17]. At Chapada dos Veadeiros National Park, in central Brazil, Horned Sungems were observed consuming nectar of abundant flowers of eight shrubs and herbs in rocky and shrubby grasslands [18]. In western Cerrado, this species was considered a nectar robber of two plant species [19].

Typically, Horned Sungems build cup-shaped nests on forking branches of small shrubs [14]. At Distrito Federal, its breeding season was considered to occur between June and October [16], while the period of nesting activity was estimated to be April and May [20]. As results of these studies differ at some extension, and their observations were based on few nests found in only two protected areas at Distrito Federal, it is likely that the breeding season of the Horned Sungem in the Cerrado has been underestimated. We supposed that the paucity of information on its breeding aspects could be mitigated through the use of citizen science data, similarly as has been conducted for other bird species in Brazil [21, 22]. This study aimed to examine breeding aspects of the Horned Sungem in the Brazilian Cerrado using data from citizen science. We focused on the breeding season, and clutch and brood sizes.

Results

We examined 2048, 276 and 34 photographs of the Horned Sungem deposited in the WikiAves, eBird and iNaturalist databases, respectively. Of these, 35 breeding records (1.5%) were gathered in the Brazilian Cerrado between 2008 and 2022, and included in this study. Most of them (89%) were gathered in the WikiAves database. They were obtained in 16 municipalities located mainly in central and southeastern Cerrado. Distrito Federal, and Minas Gerais state were the regions with more records (Appendix).

Nests were cup-shaped, and were fixed to shrubs by building their lateral sides around 2-3 inclined forking branches. Twenty-two breeding records (63%) involved nests, while a minor portion (37%) referred to young photographed outside nests (Table 1). Those regarding nests involved nest building, incubation, exposed eggs, and downy and greenish young, and occurred in comparable numbers. Only female adults were associated with nests or young. On these occasions, a female was photographed building a nest, incubating eggs, or feeding young in nests or outside them (Table 1, Appendix). Clutch size was two eggs (n = 6). Among the 10 nests with young, three had one, while other seven nests had two young.

Most breeding records (n = 23, 66%) occurred in the dry season, and fewer of them (n = 12, 34%) were obtained in the wet season (Figure 2, Appendix). They were concentrated throughout the whole dry season (May-September), and the late rainy season (March-April), having occurred scarcely in other periods of the year. Nest building was recorded along a 5-month period (early March to early July). Most records involving exposed eggs or an incubating adult also occurred during this period that involved the late rainy season and the first half of the dry season. Downy young were observed from early March to mid-July. In agreement with young development, greenish young were found in nests about 20-

30 days later – from early April to early August. Greenish young outside nests occurred along a longer (seven months) period, that comprised the late rainy season, the whole dry season, and the early rainy season (Figure 2).

Click to enlarge

Figure 2: Seasonal distribution of records with evidence of breeding activities of the Horned Sungem (Heliactin biophus) in the Brazilian Cerrado, and obtained by citizen scientists between 2008 and 2022. Data was gathered in the WikiAves, eBird and iNaturalist databases in April 2022. Arabic numerals after each month represent three periods–(I): days 1–10, (II): days 11–20, (III): days 21–31 of each month. The horizontal bars in light and dark blue colors indicate the length of the dry and rainy seasons in the Cerrado, respectively.

Discussion

This is the first study to examine breeding aspects of the Horned Sungem over a large spatial scale. This is because previous studies investigated its breeding in detail only in two protected areas located at Distrito Federal, central Brazil: the Reserva Ecológica do IBGE [16] and the Estação Ecológica de Águas Emendadas [20]. In contrast, breeding records were obtained by citizen scientists in several states and numerous localities, leading to a better representativeness of its geographic distribution than in these previous studies. Also, our study is the first to consider data obtained over a long temporal scale (15 years), as other studies involved only nests found in 1-2 years [16, 20]. As a result, our study was based on the largest number of nests of the Horned Sungem until now, as other investigations were based on a few nests [16, 20].

Nests involved in our study were comparable in structure to those described previously [14]. Similarly, clutch size was two eggs, as noted in other studies [14, 16, 20]. This number of eggs is in agreement with the finding of 1-2 young in nests of our study. Also in agreement with the literature [14], only females (not males) were associated with nests and young in our breeding records. However, as we could not monitor nests, and other studies were based on a few nests, further observations by ornithologists and citizens scientists would be necessary for a more solid conclusion about the role of both parents in the breeding activities.

The breeding season of the Horned Sungem was considered to occur between June and October in central Cerrado [16]. In this same region, its nesting period was estimated to last between April and May [20]. Our results indicate that both studies underestimated the duration of these periods for the Cerrado. First, several breeding records of our study occurred between January and April, and involved a range of phases of the breeding season (nest building to greenish young in nests). This indicates that the onset of the breeding season is not June, as proposed by Negret, et al. [16]. Also, records obtained by citizens that involved nesting activities occurred between January and August, a period substantially longer than that estimated by Marini, et al. [20]. We consider probable that differences between our and their studies regarding spatial and temporal scales contributed to these differences mentioned above.

Considering a 13-days long incubation [14], and our records involving nest building and eggs/ incubation, nesting activities by the Horned Sungem might start along seven months (January to July) in the Brazilian Cerrado. Thus, earlier phases of the breeding season (e.g. pairing, courtship and copulation) might occur since January or even December; observations of these three activities would indicate the onset of the breeding season. Considering the incubation period and a 20-22 days fledging period [14], the occurrence of our records associated with early nesting activities (nest building to incubation) is in agreement with the later occurrence of breeding records with downy and greenish young observed. Our records of greenish young outside nests indicate that the breeding season of the Horned Sungem might end in October, at the latest, in agreement with Negret, et al. [16]. However, the breeding season might finish in earlier months (since April), as supported by records of females feeding young in a few months. The observed sequence of breeding records representing different phases of the breeding season (e.g. incubation or downy young) indicates that our approach of considering citizen science data was adequate to examine this breeding aspect of the Horned Sungem in the Cerrado. Also, our data indicates that pairs can have their breeding activities occurring in different periods within the breeding season (January-October) of the species in the Brazilian Cerrado. Future studies could try to investigate the biotic (e.g. bird age) and abiotic (e.g. elevation) factors that lead to this variation in the occurrence of breeding activities by different pairs during this 10-months period.

We suggest that Brazilian ornithologists make an intense use of the photographic records available in citizen science databases regarding Brazilian birds. Wikiaves and, less expressively, eBird Brasil appear to provide excellent datasets for the study of breeding aspects of the national avifauna. Therefore, we reinforce previous studies [4, 21, 22, 29, 30] that pointed out that citizen scientists can substantially contribute for the conduction of research by professional ornithologists in Brazil.

Authors Contributions

Dárius P. Tubelis (idealization, conceptualization, data collection and analysis, interpretation and writing); Luiz Gonzaga A. Mendonça (idealization, conceptualization, data collection and analysis, interpretation and writing); Thiago J. Cardoso (conceptualization, data collection and analysis, interpretation and writing).

Conflicts of Interest

The authors declare that there are no conflicts of interest.

Acknowledgements

We thank Universidade Federal Rural do Semi-Árido (UFERSA), Conselho Municipal do Meio Ambiente, and SICOOB for logistic support. We are grateful to all citizens that deposited photographs of the Horned Sungem in the WikiAves, eBird and iNaturalist databases. Especially, we thank Fernanda Fernandes, Lorenzo Palma, Mauríllio de Carvalho and Sandra Beatriz Zarur for giving permission to include photographs of their authorship in this paper. The Editorial Committee, two anonymous reviewers and Adriano Campos improved this manuscript with numerous suggestions.

Funding

There was no funding.