Exploring food preferences and the limits of feeding flexibility of seed-eating desert birds

Abstract

Habitat degradation caused by cattle grazing may be a serious threat for seed-eating birds because the availability of beneficial seeds usually diminishes in grazed areas. Ecologically plastic species might, however, circumvent food deprivation via changes in foraging behaviour. We studied the limits of feeding flexibility and factors affecting seed preferences in Zonotrichia capensis, Diuca diuca, and Saltatricula multicolor. We experimentally assessed preferences for seeds of eight grass and eight forb species by using a protocol that combines choice and non-choice trials, and employed a different batch of experiments to evaluate some plausible causes of different feeding flexibility. On average, birds consumed 45-140% more grass than forb seeds, confirming previous results. Z. capensis preferred several grass and forb seeds, and showed maximum feeding flexibility. S. multicolor and, to a lesser extent, D. diuca, were grass specialists that preferred large and medium-sized grass seeds. The size of forb seeds did not affect preferences. Coat thickness of grass seeds did not seriously reduce consumption levels. Birds showed low ability to feed on resources characteristic of degraded environments (i.e. annual grass seeds). Species-specific differences in behavioural flexibility could be used to predict dietary and numerical responses of seed-eating birds to habitat degradation.

Do neophobia and dietary wariness explain ecological flexibility? An analysis with two seed‐eating birds of contrasting habits

“…Although our experiments highlight similar responses to novelty by both the species tested, some results would support the DNH, in particular the idea that organisms feeding on potentially dangerous food will show high levels of neophobia. The species that showed longer latencies, the rufous‐collared sparrow, is a diet generalist that can consume both grass and forb seeds in the Monte desert (Marone et al , Camín et al ), whereas the many‐colored chaco‐finch is a grass‐seed specialist that would rarely face dangerous food in the field since, on average, grass seeds have less toxic secondary compounds than forb seeds (Díaz , Ríos et al ). The tendency of the rufous‐collared sparrow to develop higher neophobia or wariness (Fig.…”

“…Knowledge of the causes of foraging flexibility is an important issue for basic and applied ecology (Charmantier et al ), since the establishment of the limits of behavioral flexibility would allow predictions to be made about population responses to global change (Camín et al ). The idea of neophobia and wariness as plausible causes of ecological specialization sounds attractive because of its simplicity and explanatory power.…”

Are all patches worth exploring? Foraging desert birds do not rely on environmental indicators of seed abundance at small scales

“…The presence of tall trees, irrespective of the main underlying cause, seems to determine a first level of selection that defines explorable space, and then microhabitat structure exerts an influence on which patches are effectively exploited (or more frequently visited), not an unusual conclusion for small ground-foraging birds (e.g., [5, 76, 109, 110]). This two-scale use of foraging space, matching the two modes of movement of these small birds within a stratified habitat (flying between perches and from perches to the ground, and walking on the ground while foraging) could result in a scenario of heterogeneous removal of seeds, particularly for the grasses these birds prefer [53, 54]. In a seed-limited environment (as this one [24]), this may cascade to a top-down effect on the spatial distribution of plant populations.…”

“…Most studies on the impact of granivores on desert seed banks have emphasised the impact of rodents and ants (e.g., [17, 43–45]), presumably as an historical consequence of the “irrelevance” of birds on deserts of the Northern Hemisphere ([46–48], but see [32, 38, 49, 50]). However, seed-eating birds should be able to modify abundance, composition and spatio-temporal heterogeneity of the soil seed bank in arid areas where they are important granivores, especially because their diet is usually selective (e.g., [51–54]). In the Monte desert, postdispersal granivorous birds are important consumers of their preferred grass seeds, especially in autumn–winter [53–56].…”

Effects of livestock grazing on flocks of seed-eating birds in the central Monte desert, Argentina

“…Studies that analyzed human impact on flocks were carried out in tropical and northern temperate environments, where flocks are comprised mainly of insectivorous birds, and where nuclear species (i.e., species that appear to facilitate flock formation, lead groups, and occur in a high proportion on flocks; Goodale and Beauchamp 2010) are also insectivores (Zou et al 2018). Current Medium to large grass seeds are the selected and preferred food for seed-eating birds in the Monte desert (Cueto et al 2006;Marone et al 2008;Camín et al 2015).…”