Risk sensitivity in starlings: variability in food amount and food delay

Starlings' preferences for constant versus variable food sourceswere studied in the laboratory. The constant alternative gavea fixed amount of food after a fixed delay. The variable alternativeoffered either a varying amount of food after a fixed delay(treatment A) or a fixed amount of food after a variable delay(treatment B). In both treatments the ratio of amount of foodover trial length (the sum of intertrial interval plus delayand handling times) of the constant alternative equaled theaverage of the two ratios of the variable alternative. The variableratios were 30% higher and 30% smaller than the fixed ratio.In free-choice trials (both options available in each trial),the subjects were risk-averse or indifferent in treatment Aand indifferent or riskprone in treatment B. In no-choice trials(only one source available per trial), the latency to respondwas longer in the variable than in the constant source in treatmentA and the opposite in treatment B. The greater preference forvariability in time than for variability in reward amount isnot consistent with either maximizing the ratio of expectedenergy over expected time or the expected ratio of energy overtime for individual trials. There was a negative correlationbetween individual intake rate and degree of risk pronenessfor both kinds of variability. We present a model of choicebased on an information-processing theory for temporal memorythat accounts for the different effects of variability in delayand in amount but cannot explain the effects of intake rate.[Behav Ecol 1991;2:301–308]     

Do sex ratio and development differ in sexually size‐dimorphic shiny cowbirds (Molothrus bonariensis) parasitizing smaller and larger hosts?

Two possible patterns of bias in primary sex ratio have been proposed for size‐dimorphic brood parasites that do not evict host chicks: (1) larger males should be laid at greater frequency in hosts larger than the parasite because they compete better (increasing their survival) than females with large host nest‐mates, and (2) more costly males (i.e. the larger sex) should be laid at greater frequency in hosts smaller than the parasite because, in these hosts, parasite nestlings are provisioned at a higher rate and grow faster than in larger hosts. We tested these hypotheses in two hosts of the sexually size‐dimorphic shiny cowbird, Molothrus bonariensis, one smaller (house wren, Troglodytes aedon) and one larger (chalk‐browed mockingbird, Mimus saturninus) than the parasite. We measured: (1) sex ratio at laying; (2) development of sexual differences in body mass during the nestling stage; and (3) chick survival and sex ratio of chicks before fledging. In both hosts, we found sexual differences in body mass of nestlings from 7 days of age onwards, although we did not find a bias in the sex ratio of eggs laid and chicks fledged. The results of the present study do not support the hypothesis that shiny cowbird females benefit from biasing the primary sex ratio depending on the size of the hosts they parasitize. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 442–448.     

Effects of fragmentation and hybridization on geographical patterns of song variation in the endangered Yellow Cardinal Gubernatrix cristata

The song learning process may lead to small‐scale geographical variation in vocalizations of oscine birds. This variation can be further enhanced by the effects of habitat fragmentation or hybridization. Populations of the endangered Yellow Cardinal Gubernatrix cristata are now patchily distributed in the southern South American thorny shrubland forests and are small as a consequence of the pressure exerted by increased habitat transformation and illegal trade. We study the Yellow Cardinal's vocalizations throughout its distribution and assess how habitat characteristics and fragmentation, as well as hybridization with the Common Diuca Diuca diuca, have affected song patterns of different populations. We expected to find song differences among populations and songs to be more similar to those of the Common Diuca in areas where hybridization occurs. Multivariate analyses revealed significant differences in song between the four populations studied and confirmed that songs are more similar to those of Common Diuca where hybridization takes place. These results, in conjunction with genetic studies, can help to establish management units that preserve genetic and cultural variation in this endangered species.     

Genetic structure reveals management units for the yellow cardinal (<Emphasis Type="Italic">Gubernatrix cristata</Emphasis>), endangered by habitat loss and illegal trapping

The yellow cardinal, Gubernatrix cristata, is an endangered passerine from southern South America. Populations are declining due to the loss of their natural habitat, which has caused a fragmented distribution, and the continuous extraction of individuals from the wild, mainly males, to sell them as cage birds. In this study, we assess the genetic variability of remaining yellow cardinal’s populations and determine whether these populations represent independent management units. We found that the degree of geographic isolation of the remaining populations parallels the genetic differentiation of these populations for both mitochondrial and nuclear markers, and supports the delimitation of four management units for the yellow cardinal (three in Argentina and one in Uruguay). Assignment tests showed that geographic genetic differentiation can be used to assign seized individuals from illegal pet trade to their original populations and thus manage their release.     

Roosting behaviour is related to reproductive strategy in brood parasitic cowbirds

Shiny Cowbirds Molothrus bonariensis and Screaming Cowbirds Molothrus rufoaxillaris are closely related brood parasites but the former is socially polygynous or promiscuous and an extreme host generalist, whereas the latter is socially monogamous and parasitizes almost exclusively one host. Females of both species lay in relative darkness, before dawn, relying for host nest location on previous days’ prospecting activity, or possibly on following better‐informed roost associates. We studied the temporal and spatial patterns of roosting behaviour in these species to test the hypothesis that roosting behaviour of cowbirds is related to their breeding strategy (brood parasitism) and reflects differences in strategies between species. We recorded fidelity to a roost, location fidelity within a roost, inter‐individual spatial associations and timing of roost departures and parasitic events, using tagged individuals. Female Shiny Cowbirds and both sexes of Screaming Cowbirds showed marked fidelity in roosting location, and roost departures occurred both during and after the known time window for parasitism, with earlier departures probably corresponding to laying days. Screaming Cowbird females and males that were trapped together and showed high levels of association during the day, also showed high levels of association in the roost. We describe the spatial and temporal patterns of a relatively poorly known aspect of avian ecology in general and the behaviour of brood parasites in particular.     

Molecular tracking of individual host use in the Shiny Cowbird – a generalist brood parasite

Generalist parasites exploit multiple host species at the population level, but the individual parasite's strategy may be either itself a generalist or a specialist pattern of host species use. Here, we studied the relationship between host availability and host use in the individual parasitism patterns of the Shiny Cowbird Molothrus bonariensis, a generalist avian obligate brood parasite that parasitizes an extreme range of hosts. Using five microsatellite markers and an 1120‐bp fragment of the mtDNA control region, we reconstructed full‐sibling groups from 359 cowbird eggs and chicks found in nests of the two most frequent hosts in our study area, the Chalk‐browed Mockingbird Mimus saturninus and the House Wren Troglodytes aedon. We were able to infer the laying behavior of 17 different females a posteriori and found that they were mostly faithful to a particular laying area and host species along the entire reproductive season and did not avoid using previously parasitized nests (multiple parasitism) even when other nests were available for parasitism. Moreover, we found females using the same host nest more than once (repeated parasitism), which had not been previously reported for this species. We also found few females parasitizing more than one host species. The use of an alternative host was not related to the main hosts' nest availability. Overall, female shiny cowbirds use a spatially structured and host species specific approach for parasitism, but they do so nonexclusively, resulting in both detectable levels of multiple parasitism and generalism at the level of individual parasites.     

Beta-adrenergic control of the water permeability of the skin during rehydration in the toad Bufo arenarum.

1. Toads dehydrated to 80% of their standard weight (% SW) were rehydrated during 3 hr in distilled water. 2. Water permeability of the skin was positively correlated with the degree of dehydration in the range 80-100% SW. 3. Systemic administration of the beta-adrenergic agonist isoproterenol (5 mg/kg) 90 min after rehydration started (animals fully hydrated) increased skin permeability to the values observed in 80% SW dehydrated animals. 4. The administration of the beta-adrenergic blocker propranolol (5 mg/kg) 15 min before rehydration started produced a long-lasting decrease in water permeability during the 3 hr of rehydration. 5. The results are consistent with the hypothesis of a beta-adrenergic control of the water permeability of the skin during rehydration.     

Antidiuretic responses to osmotic cutaneous stimulation in the toad,Bufo arenarum

Summary Osmotic stimulation of the skin of the toadBufo arenarum with isotonic (115 mM) or hypertonic (400 mM) NaCl solutions produced a marked and reversible antidiuresis within 5 min. No changes in plasma osmolarity were detected in the course of this response.Hypophysectomized animals exhibited a lower and delayed antidiuresis when exposed to a hypertonic environment (400 mM NaCl). This antidiuretic response was drastically reduced in normal toads after ten consecutive days of administration of the sympatoplexic guanethidine.The existence of a feed-forward control of urine production initiated by cutaneous osmotic sensors and involving an adrenergic component is proposed.     

A recent invasive population of the European starling sturnus vulgaris has lower genetic diversity and higher fluctuating asymmetry than primary invasive and native populations

Biological Invasions - Fluctuating asymmetries (FA) are small stress-induced random deviations from perfect symmetry that arise during the development of bilaterally symmetrical traits. One of the...