Differences in insectivore bird diets in coffee agroecosystems driven by obligate or generalist guild, shade management, season, and year

Neotropical shade-grown coffee systems are renowned for their potential to conserve avian biodiversity. Yet, little is known about food resources consumed by insectivorous birds in these systems, the extent of resource competition between resident and migratory birds, or how management of shade trees might influence diet selection. We identified arthropods in stomach contents from obligate and generalist insectivorous birds captured in mist-nets at five coffee farms in Chiapas, Mexico between 2001–2003. Overall stomach contents from 938 individuals revealed dietary differences resulting from changes in seasons, years, and foraging guilds. Of four species sampled across all management systems, Yellow-green Vireo (Vireo flavoviridis) prey differed depending on coffee shade management, consuming more ants in shaded monoculture than polyculture systems. Diets of obligate and generalist resident insectivores were 72% dissimilar with obligate insectivores consuming more Coleoptera and Araneae, and generalist insectivores consuming more Formicidae and other Hymenoptera. This suggests that obligate insectivores target more specialized prey whereas generalist insectivores rely on less favorable, chemically-defended prey found in clumped distributions. Our dataset provides important natural history data for many Nearctic-Neotropical migrants such as Tennessee Warbler (Leiothlypis peregrina; N = 163), Nashville Warbler (Leiothlypis ruficapilla; N = 69), and Swainson’s Thrush (Catharus ustulatus; N = 68) and tropical residents including Red-legged Honeycreepers (Cyanerpes cyaneus; N = 70) and Rufous-capped Warblers (Basileuterus rufifrons; N = 56). With declining arthropod populations worldwide, understanding the ecological interactions between obligate and generalist avian insectivores gives researchers the tools to evaluate community stability and inform conservation efforts.

Sexual dimorphism in bat wing morphology – variation among foraging styles

Sexual dimorphism can lead to differences in foraging style among conspecifics due to morphological differences. Within bats, maneuverability and speed of flight are influenced by wing shape and size, which may differ between sexes. Female bats gain about 30% of their body mass during pregnancy, affecting their agility and flight efficiency. To fill the same foraging niche as males, pregnant female bats would require wing size and/or shape modifications to maintain maneuverability. We investigated sexual dimorphism in bat wing morphology and how it varies among foraging guilds. Wing photos of male and female adult bats (19 species) in Canada, Belize, and Dominica were analyzed using 2D geometric morphometrics, wing loading, and aspect ratios. Nonpregnant female bats had higher wing loading than males, suggesting they are less maneuverable than males. Additionally, mass increases during pregnancy may not permit female bats to forage as male conspecifics do. Wing shape differed minimally among foraging guilds with only frugivores differing significantly, from all other guilds. Further studies should investigate how female bats forage during their reproductive cycle and determine how frugivore wings differ and whether there are individual differences in wing shape that are not consistent among bat species.

Isotopic Niche Segregation among Darwin’s Finches on Santa Cruz Island, Galápagos

Darwin’s finches are a classic example of adaptive radiation involving differential use of dietary resources among sympatric species. Here, we apply stable isotope (δ13C, δ15N, and δ2H) analyses of feathers to examine ecological segregation among eight Darwin’s finch species in Santa Cruz Island, Galápagos collected from live birds and museum specimens (1962–2019). We found that δ13C values were higher for the granivorous and herbivorous foraging guilds, and lower for the insectivorous finches. Values of δ15N were similar among foraging guilds but values of δ2H were higher for insectivores, followed by granivores, and lowest for herbivores. The herbivorous guild generally occupied the largest isotopic standard ellipse areas for all isotopic combinations and the insectivorous guild the smallest. Values of δ2H provided better trophic discrimination than those of δ15N possibly due to confounding influences of agricultural inputs of nitrogen. Segregation among guilds was enhanced by portraying guilds in three-dimensional isotope (δ13C, δ15N, and δ2H) space. Values of δ13C and δ15N were higher for feathers of museum specimens than for live birds. We provide evidence that Darwin’s finches on Santa Cruz Island tend to be generalists with overlapping isotopic niches and suggest that dietary overlap may also be more considerable than previously thought.

Occupancy of avian foraging guilds in soybean fields and borders in Entre Ríos, Argentina: responses to vegetation structure and prey resources

Background Reconciling agriculture and biodiversity conservation is a challenge given the growing demand for agricultural products. In recent decades, Argentina has witnessed agricultural expansion and intensification affecting biodiversity and associated ecosystem services. Within agroecosystems, the level of habitat quality is critical for birds, and may depend on vegetation structure, availability of invertebrate prey, and the use of pesticides. Although the relationship between vegetation structure and avian occurrence has been widely studied, to our knowledge, there are no studies that also incorporate prey availability throughout the cycle of soybean crops in Argentina. We estimated and predicted the effects of land cover and temporal variation on the occurrence of avian foraging guilds in Entre Ríos, Argentina, in order to guide management related to potential ecosystem services provided by birds. We also estimated temporal effects of vegetation structure and insecticides on the main arthropod orders consumed by birds to evaluate prey availability. Methods We conducted bird and arthropod surveys for 2 years along transects located in 20 randomly selected soybean fields (N = 60) and their adjacent borders (N = 78) throughout the crop growing season, in four seasons. We estimated avian occupancy, accounting for imperfect detection, and arthropod counts fitting generalized linear mixed models. Results The number of native trees in field borders positively influenced the occurrence of most bird species, mainly insectivores. Granivore foliage gleaners, also were positively affected by grass height. Salliers and aerial foragers were weakly affected by distance to forest and native trees. In general, the availability of invertebrates to birds was highest during the third season. Arthropod counts in borders were greater during the last three crop stages than during the pre-sowing period. Conclusions We found that with 10 to 15 native tree species in borders, coupled with a complex vegetation structure with shrubs and grasses, we could conserve a wide spectrum of insectivorous birds, and may contribute to the invertebrate pest control service. Vegetated field borders function as a refuge for arthropods, especially agriculturally beneficial taxa such as Hymenopterans. Finally, several groups of birds use the interior of the fields and could help control pests.

Comparing mesophotic and shallow reef fish assemblages in the 'Au'au Channel, Hawaii: fish size, feeding guild composition, species richness, and endemism

Mesophotic (30–150 m) reef fish assemblages in the 'Au'au Channel, between the Hawaiian Islands of Maui and Lanai, were compared visually with neighboring shallow (<30 m depth) reef fish assemblages for differences in structure. Between 2007 and 2011, approximately 7000 mesophotic and 4000 shallow reef fishes were identified, sized (standard length), and assigned to seven foraging guilds. The shallow water zone had more species than the mesophotic zone (99 vs 80, respectively). Mesophotic planktivores and two herbivore species were significantly larger than their shallow reef counterparts. Shallow reef fish assemblages had a higher Chao1 estimated species richness for herbivores and corallivores but not the other five foraging guilds. The differences between mesophotic and shallow fish assemblages indicate that both have unique communities of high conservation importance.

Composition, diversity and foraging guilds of avifauna in agricultural landscapes In Panipat, Haryana, India

Avian communities are very good indicators of integrity and stability of ecosystem structure and functions. Assessment of bird assemblages in different landscapes is therefore emphasized from an environmental monitoring viewpoint. Bird surveys were carried out from April 2015 to March 2016 to document the avian species assemblage of agricultural landscapes in Panipat, Haryana, India. Point-transect in amalgam with opportunistic encounter methods were used to collect data. A total of 101 bird species under 44 families and 15 orders were recorded from the study area. The bird species richness was highest for the order Passeriformes (48), followed by Pelecaniformes (15), Charadriiformes (6), and the remaining 12 orders. Ardeidae was the most diverse bird family in the study area. Among the recorded avifauna, 77 species were residents, 18 species were winter migrants and six species were summer migrants. Species richness was recorded to be highest in the month of January compared to the remaining months. Species richness, abundance, diversity and evenness differed significantly (P < 0.05) between seasons as well as among the agricultural landscapes. Most bird species were insectivorous (36) followed by carnivorous (26), omnivorous (24), granivorous (9), frugivorous (5) and nectarivorous (1). Painted Stork Mycteria leucocephala, Black-necked Stork Ephippiorhynchus asiaticus, Black-headed Ibis Threskiornis melanocephalus, and Alexandrine Parakeet Psittacula eupatria are four Near Threatened species found in this region. Interestingly, five species having globally declining population trends are still common in the study area. The observed richness of avian species in the study area calls for further studies on habitat preference, seasonal changes, nest ecology, and breeding biology to understand species specific roles of birds in agro-ecosystems.

Waterbirds in the panhandle of the Okavango Delta: dry season counts over two seven-year periods

We counted waterbirds along a fixed route in the panhandle of the Okavango River in Mahango Game Reserve in the dry season during two seven-year periods (1991–1997 and 2000–2006). Palearctic migrants represented by 11 species in 1991–1997 and nine species in 2000–2006 together composed only a small percentage of all birds recorded in both periods. The two most numerous foraging guilds were birds foraging in shallow water and those foraging in deep water. The former guild was more numerous in 2000–2006, while the latter guild was more numerous in 1991–1997. The proportion of other foraging guilds varied little between the two periods. The most numerous diet guild was piscivores, they were more numerous in 1991–1997 than in 2000–2006. If the total numbers of birds of each particular species in the years 1991–1997 were pooled and compared with those for the years 2000–2006, then highly significant changes in their numbers between these periods could be seen for 53 out of 93 waterbird species. Over the timespan 1991–2006, 12 species significantly increased in numbers while one species, the Cattle Egret, declined; seven other species showed no significant changes in abundance. The increase can be linked to the volume of water flowing through the river. While during the years 1991–1997 the total volume measured at Mohembo was 45.9 km3 (SD = 1.43), during the years 2000–2006 the volume was 60.9 km3 (SD = 1.41). Diversity was very similar during the two periods (1991–1997: S = 1.4; 2000–2006: S = 1.3), with no difference in evenness. The striking feature is that species diversity and abundance of birds was far greater than any records from other southern African rivers to date.

Bats from different foraging guilds prey upon the pine processionary moth

Outbreaks of the processionary moth Thaumetopoea pityocampa (Denis & Schiffermüller, 1775), a forest pest from the Palearctic, are thought to induce a behavioral response of bats, but up to now the moth has been seldom identified as bats’ prey. Studies on bat diets suggest moths with cyclical outbreaks attract a wide array of bat species from different foraging guilds. We test whether bats feed upon T. pityocampa in the Iberian Peninsula irrespective of the predator’s ecological and morphological features. We found that seven out of ten bat species belonging to different foraging guilds contained T. pityocampa DNA in their faeces and no difference was found in the foraging frequency among foraging guilds. A different size of the typical prey or the lack of fondness for moths can explain the absence of the pest in some bat species. Moreover, the intraspecific foraging frequency of T. pityocampa also changed with the sampling site likely representing differential availability of the moth. Lack of information on flight and dispersal behavior or the tympanate nature of the adult moth complicates understanding how different foraging guilds of bats prey upon the same prey. Our data suggests that T. pityocampa is a remarkable food source for many thousands of individual bats in the study area and we anticipate that more bats besides the species studied here are consuming this moth.