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.
Th e fi rst information on the gestation period, maternal behaviour, neonatal development and growth of the subterranean caviomorph rodent Ctenomys mendocinus Philippi, 1869, is reported herein. My hypothesis was that, despite its belonging to a typically precocial suborder, the life history traits of C. mendocinus would favour its altricial condition. Th e off spring of C. mendocinus were categorized as altricial by using two diff erent classifi cation systems. Th is condition was also refl ected in maternal care. Females built large nests (2000 cm 3 ) where, after a long gestation period (95.9 days), they gave birth to litters of blind pups, half-naked, with external ear meatus open and good physical coordination. Th e mothers suckled the off spring in long bouts (19.9 min), retrieved their pups, and these showed no tactics to reduce the suckling bout. Overall, evidence was consistent with the hypothesis analyzed, although particularities found, e.g. some precocial traits, suggest the existence in C. mendocinus of a trade-off between the constraints and advantages related to its subterranean way of life and the phylogenetic inertia typical of caviomorphs.
The neophobia threshold hypothesis (NTH) suggests that the acquisition and maintenance of a high behavioral and ecological flexibility in the evolutionary and adaptive history of a species is the consequence of lower levels of neophobia towards new micro-habitats and of dietary wariness of novel foods. To test this idea we assessed the degree of neophobia and dietary wariness in two seed-eating bird species with contrasting degrees of ecological flexibility that inhabit the central Monte desert (Argentina): a grass-seed specialist, the many-colored chaco-finch, and a generalist feeder, the rufous-collared sparrow. We expected that both species would exhibit neophobia and wariness when faced with new foraging opportunities but that the rufous-collared sparrow would be less neophobic and less wary than the specialized many-colored chaco-finch. Experimental indicators of neophobia and dietary wariness included willingness to eat near novel objects and willingness to eat novel seeds, respectively. Both species showed similar levels of reluctance to novelty, although the sparrow could be slightly more reluctant than the finch. Contrary to our predictions, the sparrow was neither less hesitant nor faster or greedier than the finch. This experimental evidence does not support a negative relationship between neophobia/wariness and ecological flexibility in these two seed-eating birds and it coincides with the growing evidence that challenges the NTH. Some of our results provide support for the dangerous niche hypothesis, especially as the rufous-collared sparrow, that feeds on more diverse and potentially dangerous food, showed higher levels of neophobia in some cases. Although the idea of neophobia and wariness being plausible causes of ecological specialization sounds attractive, the current situation calls for further research so that the causes of ecological flexibility in granivorous birds can be better understood.
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