Alan Lill

Behavioural responses of wildlife to urban environments

Increased urbanization represents a formidable challenge for wildlife. Nevertheless, a few species appear to thrive in the evolutionarily novel environment created by cities, demonstrating the remarkable adaptability of some animals. We argue that individuals that can adjust their behaviours to the new selection pressures presented by cities should have greater success in urban habitats. Accordingly, urban wildlife often exhibit behaviours that differ from those of their rural counterparts, from changes to food and den preferences to adjustments in the structure of their signals. Research suggests that behavioural flexibility (or phenotypic plasticity) may be an important characteristic for succeeding in urban environments. Moreover, some individuals or species might possess behavioural traits (a particular temperament) that are inherently well suited to occupying urban habitats, such as a high level of disturbance tolerance. This suggests that members of species that are less ‘plastic’ or naturally timid in temperament are likely to be disadvantaged in high‐disturbance environments and consequently may be precluded from colonizing cities and towns.

Longevity Records for Some Neotropical Land Birds

on survival rates in the tropics. Snow (1962a) found that male White-bearded Manakins (Manacus manacus) in Trinidad had an annual survival rate of at least 89%. This was based on a group of established adult males holding courts at a lek, which were followed over a 3-year period. An indirect estimate for the Golden-headed Manakin (Pipra erythrocephala), another lek-forming species, based on the proportions of males, females, and young birds in a trapped population, gave a similar figure (Snow 1962b). Fogden (1972) calculated a minimum annual survival rate of 86% for a sample of birds of many different species trapped in a forest in Sarawak, Borneo. These percentages are far higher than those recorded for European and North American passerines, for which annual survival rates of adults are predominantly in the 30-50% range (Lack 1954, Table 21). They are in fact much closer to the very high survival rates of the larger seabirds. Fogdens figure was based on one year only, during which conditions might have been either better or less good than usual. Snows data for the manakins were based on

Interpreting indices of physiological stress in free-living vertebrates

When vertebrate physiological ecologists use the terms ‘stress’ or ‘physiological stress’, they typically mean the level of hypothalamus–pituitary–adrenal (HPA-) axis activation. Measurements of stress hormone concentrations (e.g. glucocorticoids in blood, urine or faeces), leukocytes (e.g. the neutrophil–lymphocyte ratio or heterophil equivalent), immunofunction (e.g. innate, cell-mediated or humoral immunity measures) and regenerative anaemia (e.g. mean erythrocyte volume and red blood cell distribution width) have all been used to estimate HPA-axis activity in free-living vertebrates. Stress metrics have provided insights into aspects of autecology or population regulation that could not have been easily obtained using other indices of population wellbeing, such as body condition or relative abundance. However, short- and long-term stress (often problematically termed acute and chronic stress, respectively) can interact in unpredictable ways. When animals experience trapping and handling stress before blood, faeces and/or urine is sampled, the interaction of short- and long-term stress can confound interpretation of the data, a fact not always acknowledged in studies of stress in free-living vertebrates. This review examines how stress metrics can be confounded when estimates of HPA-axis activation are collected for free-living vertebrates and outlines some approaches that can be used to help circumvent the influence of potentially confounding factors.

Fruit color choices of captive silvereyes (Zosterops lateralis)

Fleshy fruits occur in many colors in nature, but red and black predominate. One popular hypothesis to explain the adaptive significance of fruit coloration is that it attracts frugivorous birds that disperse seeds. We presented Silvereyes (Zosterops lateralis), important fruit consumers in southern Australia, with choices in the aviary between both artificial fruits (made from gelatin) and actual fruits (Rhagodia parabolica) of three different colors (red, yellow and white). Silvereyes exhibited a strong overall preference for red among both artificial and real fruits. Although individual birds varied in their color preferences for artificial fruits, all preferred the red fruits of R. parabolica. The consumption rate of real fruits was much greater than that of artificial fruits, which was probably attributable to differences in the characteristics of the two fruit types. Exposure of Silvereyes to a maintenance diet of a particular color for 12 days also failed to alter their collective preference for red fruits. Further, responses to artificial infructescences offering color choices either between or within infructescences showed that Silvereyes preferred red fruits regardless of the spatial format of presentation. The overall fruit color preferences of Silvereyes were based on selection of hue rather than brightness, but within the same hue, some individuals exhibited preferences for particular brightness levels. These results are consistent with the hypothesis that fruit color is related to avian frugivory and suggest that birds can act as strong selective agents on fruit color.

Spatial Organisation in Small Flocks of Domestic Fowl

(i) Spatial organisation was studied in small flocks of domestic fowl to elucidate its underlying mechanisms and provide a basis for future comparative analyses. (ii) Approach-tolerance distance values were obtained in a non-competitive feeding and a roosting situation. (iii) A zone of variable width across which the likelihood of approach eliciting agonistic response increased centripetally was observed around feeding birds. No sexual difference in zone width was noted, and tolerance of approach was great. (iv) No indication of constant Individual Distance in roosting birds was obtained, though spatial adjustment following agonistic interaction was observed. Clumping was common. (v) Activity-dependent variability in spatial organisation was described and correlated with the distribution of aggressive behaviour. (vi) It was postulated that the state of dispersion during specific activities was explicable in terms of the interaction of the opposed tendencies to congregate and aggregate and to react aggressively when approached. (vii) The nature and distribution of clumping and allopreening responses were described, and their causation and function discussed.

How Noisy Does a Noisy Miner Have to Be? Amplitude Adjustments of Alarm Calls in an Avian Urban ‘Adapter’

Background Urban environments generate constant loud noise, which creates a formidable challenge for many animals relying on acoustic communication. Some birds make vocal adjustments that reduce auditory masking by altering, for example, the frequency (kHz) or timing of vocalizations. Another adjustment, well documented for birds under laboratory and natural field conditions, is a noise level-dependent change in sound signal amplitude (the ‘Lombard effect’). To date, however, field research on amplitude adjustments in urban environments has focused exclusively on bird song. Methods We investigated amplitude regulation of alarm calls using, as our model, a successful urban ‘adapter’ species, the Noisy miner, Manorina melanocephala. We compared several different alarm calls under contrasting noise conditions. Results Individuals at noisier locations (arterial roads) alarm called significantly more loudly than those at quieter locations (residential streets). Other mechanisms known to improve sound signal transmission in ‘noise’, namely use of higher perches and in-flight calling, did not differ between site types. Intriguingly, the observed preferential use of different alarm calls by Noisy miners inhabiting arterial roads and residential streets was unlikely to have constituted a vocal modification made in response to sound-masking in the urban environment because the calls involved fell within the main frequency range of background anthropogenic noise. Conclusions The results of our study suggest that a species, which has the ability to adjust the amplitude of its signals, might have a ‘natural’ advantage in noisy urban environments.

Do predation rates on artificial nests accurately predict predation rates on natural nests? The effects of nest type, egg type and nest-site characteristics

Abstract We compared the predation rate on natural nests of the Eastern Yellow Robin, Eopsaltria australis, with the predation rates on four types of artificial nests in a woodland remnant in southern Victoria. The aims of this study were: to compare the overall rates of predation on artificial and natural nests; to determine whether artificial nests accurately reflect the effects of nest-site characteristics on the predation rate of natural nests; and to examine the effects of using different nest types and egg types for artificial nests. The predation rates on artificial nests were significantly greater than those on natural nests. The predation rate was significantly greater on artificially constructed nests than on real, disused Eastern Yellow Robin nests, but there was no difference in the predation rates on artificial nests containing plasticine or Canary, Serinus canarius, eggs. There were no effects of nest-site characteristics on the predation rates on either artificial or natural nests. These results showed that the method of construction of artificial nests can affect the rate of nest predation, and suggest that artificial nests should be made as realistic as possible in order to gain more accurate information on the predation rates on the natural nests they are meant to represent.

Tolerance of human approaches by Common Mynas along an urban-rural gradient

Abstract Successful urban colonisation by birds requires tolerance of many disturbances and avoidance of chronic stress and major disruption to critical activities. Habituation may be involved in acquiring tolerance of human proximity, in which case tolerance should vary with the degree of opportunity to learn that most humans do not present a threat and should therefore vary with human population density. We studied Common Mynas (Acridotheres tristis) in the urban, suburban, peri-urban and surrounding rural zones of Melbourne, Australia, to determine whether flight-initiation distance (FID) and time allocated to anti-predator vigilance increased along this gradient from the urban to the rural zone. This gradient encompassed a 143-fold variation in average human population density during daylight hours. Urban and suburban Mynas had a 2.3-5.7 times shorter FID, were 1.6-2.5 times less likely to retreat by flying and were 1.9-3.1 times more likely to flee >5 m than their peri-urban and rural conspecifics. Fleeing behaviour was not strongly correlated with estimated human population density, but exhibited an apparent ‘step’ in response at the suburban-peri-urban divide. Vigilance effort did not vary significantly between zones. This suggested that habituation did not occur with respect to surveillance for people, although surveillance presumably encompassed other predators too. Similar foraging effort and rates of food acquisition among zones could suggest that food abundance per individual was similar in urban and rural environments for Common Mynas, although this requires direct measurement.

Importance of eucalypts in exploitation of urban parks by Rainbow and Musk Lorikeets

Abstract The abundance and distribution of Rainbow (Trichoglossus haematodus) and Musk (Glossopsitta concinna) Lorikeets in Melbourne have increased markedly in recent years. We studied the feeding ecology of the two species, and their interspecific aggressive interactions, in some parks in Melbourne in spring and summer to determine how availability of food might affect the success of this urban proliferation. The diets of both species were dominated by nectar or pollen (the two were not distinguished in this study) from 5–6 species of eucalypts. Feeding on native plants not indigenous to the Melbourne region accounted for 61% and 74% of feeding records of Rainbow and Musk Lorikeets respectively. Both lorikeets foraged mainly in the tree canopy (99% of records), mostly perching upright or hanging to reach their food. Nectar and pollen were readily available through spring and summer because five important eucalypt food-plant species flowered constantly and several other food-plant species flowered for a substantial proportion of the time. There was little use of lorikeet food resources by other species of bird, and lorikeets were only involved in 3.5 interspecific aggressive encounters at feeding sites per observation week. The feeding ecology of the lorikeets in spring—summer was broadly similar to that reported for Melbourne in winter and for non-urban habitats in northern and eastern Australia. Abundant nectar and pollen from ornamental eucalypts planted in the twentieth century and the apparently low level of competitive interactions with other bird species for these resources have probably been important in facilitating the recent increase in abundance and distribution of both lorikeets in Melbourne.

Microclimate of nesting burrows of the Rainbow Bee-eater

Abstract Burrow-nesting affords protection from predators and climatic extremes, but potentially can pose physiological ‘problems’ for developing birds and attendant adults. Microclimate parameters of burrows of breeding Rainbow Bee-eaters (Merops ornatus) were measured to assess whether they presented such difficulties for young and adults. Estimated mean volume of the brood-chamber was ∼4.5 L. Relative humidity was typically 100% in the brood-chamber and chamber air temperature was constant, averaging 4–6°C above ambient levels. The temperature regime of the burrow probably resulted in low thermoregulatory costs for attendant adults and endothermic nestlings. The chamber oxygen (O2) fraction (mean 19.35%) was always lower than ambient values, but mostly not sufficiently low to be problematic for the growing young. Mean pre-internal pipping absolute oxygen consumption rate of embryos (62.9 ± 13.8 mL O2 day−1) did not appear to be strongly influenced by either the protracted incubation period or the reduced O2 partial pressure of the chamber atmosphere. Mean eggshell water-vapour conductance (8.95 mg day−1 kPa−1) was tuned to egg mass rather than egg mass/incubation period. However, eggs still lost ∼15% of their mass during incubation because the influence of the small water-vapour pressure difference across the shell (2.91 kPa) and the protraction of the incubation period apparently counteracted each other.