Gustavo A. Londoño

Urban mockingbirds quickly learn to identify individual humans.

Practically all animals are affected by humans, especially in urban areas. Although most species respond negatively to urbanization, some thrive in human-dominated settings. A central question in urban ecology is why some species adapt well to the presence of humans and others do not. We show that Northern Mockingbirds (Mimus polyglottos) nesting on the campus of a large university rapidly learn to assess the level of threat posed by different humans, and to respond accordingly. In a controlled experiment, we found that as the same human approached and threatened a nest on 4 successive days, mockingbirds flushed from their nest at increasingly greater distances from that human. A different human approaching and threatening the nest identically on the fifth day elicited the same response as the first human on the first day. Likewise, alarm calls and attack flights increased from days 1–4 with the first human, and decreased on day 5 with the second human. These results demonstrate a remarkable ability of a passerine bird to distinguish one human from thousands of others. Also, mockingbirds learned to identify individual humans extraordinarily quickly: after only 2 30-s exposures of the human at the nest. More generally, the varying responses of mockingbirds to intruders suggests behavioral flexibility and a keen awareness of different levels of threat posed by individuals of another species: traits that may predispose mockingbirds and other species of urban wildlife to successful exploitation of human-dominated environments.

Effects of temperature and food on incubation behaviour of the northern mockingbird, Mimus polyglottos

Avian incubation behaviour is thought to be influenced mainly by ambient temperature and food availability. Field studies, however, have generated contradictory results; there is little agreement about the relative importance of food and temperature and how different components of incubation behaviour are affected by them. To date, no studies have manipulated both food availability and nest temperature in a controlled experiment, making it impossible to assess any potential interaction between food and temperature. We experimentally increased both food availability and ambient temperature during incubation in the northern mockingbird. Our results show that both food availability and temperature influence incubation behaviour. Increasing food availability enabled females to spend more time on the nest and in self-maintenance activities when off the nest. Increasing nest temperature caused females to spend less time incubating and to make more trips to and from the nest. When both food and temperature were increased, their effects on incubation time offset each other. These changes in incubation patterns had little effect on fitness, although embryo mass was lowest in the treatment in which only heat was increased, suggesting that heat may stress embryos, but not when extra food is also provided. Perhaps the reason previous studies have yielded contradictory results is that food and temperature offset each other in complex ways that could obscure their individual effects. Indeed, our experiment shows that food and temperature both affect avian incubation behaviour, but that different trade-offs apply to each environmental factor.

Efficiency, bias, and consistency of visual and aural surveys of curassows (Cracidae) in tropical forests

Abstract Curassows are among the most threatened Neotropical birds, so reliable methods for estimating their abundance are needed to discern distribution patterns and manage populations. Based on the assumptions that the distance to booming curassows cannot be determined reliably and that curassow calling is unpredictable, it has been suggested that curassow abundance should be estimated only through surveys using visual cues. Based on line-transect surveys of Great Curassows (Crax rubra) conducted in a lowland tropical forest in Costa Rica, we show that distance to booming curassows can be measured accurately in the field. We also show that line-transect aural surveys sample curassows over large areas across all forest vertical strata and provide precise estimates of their abundance, but are biased towards detecting males. In contrast, line-transect visual surveys sample only small areas of forest understory and are imprecise, but appear not to be biased towards any sex or age class. We argue that the assumption that curassow calling is unpredictable is not well supported, and we recommend the use of surveys using aural cues to estimate curassow abundance efficiently.

Morphological and Behavioral Evidence of Batesian Mimicry in Nestlings of a Lowland Amazonian Bird

Because predation is the main cause of avian nest failure, selection should favor strategies that reduce the probability of nest predation. We describe apparent Batesian mimicry in the morphology and behavior of a Laniocera hypopyrra nestling. On hatching, the nestling had a distinctive bright orange color and modified feathers all over its body, and 6 days after hatching, it started to move its head very slowly from side to side (in a “caterpillar” movement) when disturbed. These traits gave it a resemblance to a hairy, aposematic caterpillar. This species has a long nestling period for its size (20 days), perhaps due to slow provisioning rates (about one feeding per hour). We argue that the slow growth rate, combined with high nest predation, favors the evolution of antipredation mechanisms such as the unique morphological and behavioral characteristics of L. hypopyrra nestlings.

NESTING RECORDS OF FIVE ANTBIRD SPECIES FROM THE COLOMBIAN AMAZON

Abstract Few nests of Amazonian antbirds (Thamnophilidae and Formicariidae) have been described. Here we present nesting records for five species of antbirds found in Tinigua National Park, Colombia. A pouch-shaped pensile nest of the Warbling Antbird (Hypocnemis cantator) in a treefall gap within seasonally flooded forest contained two eggs colored like those found in French Guiana but different from those in Amazonian Brazil and Peru. The Black-spotted Bare-eye (Phlegopsis nigromaculata) also nested in seasonally flooded forest; it constructed a cup-shaped nest inside a hollow rotten stump and laid two eggs. Two naked nestlings with bright yellow bills disappeared soon after hatching. Two cup-shaped nests of the Scale-backed Antbird (Hylophylax poecilinota) were in mature terra firme forest. Both contained two eggs similar in color to those of other subspecies; nestlings were naked and had conspicuous yellow bills. Those found in one nest disappeared 11 days after hatching. A nest of the Amazonian Streaked-Antwren (Myrmotherula multostriata) containing one egg was in seasonally flooded forest close to the river bank. This egg differed in coloration from others found in Brazil and from those of other members of the M. surinamensis complex, with which it was formerly considered conspecific. A Striated Antthrush (Chamaeza nobilis) nested in an unlined natural cavity some 3 m above the ground. The nestling closely resembled the adult but was smaller, had yellow bill commissures, and a shorter tail.

Eggs, Nests, and Incubation Behavior of the Moustached Wren (Thryothorus genibarbis) in Manu National Park, Perú

Abstract The genus Thryothorus is a wide spread genera in the Neotropics and nesting information is known for 85% of the species. I found four nests of the Moustached Wren (Thryothorus genibarbis) that were dome and bulky ball-like structures with a side entrance. All nests contained two white eggs with reddish-brown blotches. Daily nest attentiveness was 58.0% and average egg temperature was 32.5° C. Incubation behavior varied among nests and also throughout the incubation period, especially during early stages.

Energetic constraints on an early developmental stage: a comparative view

Biologists have long sought a means by which to quantify similarities and differences in embryonic development across species. Here we present a quantitative approach for predicting the timing of developmental events based on principles of allometry and biochemical kinetics. Data from diverse oviparous species support model predictions that most variation in the time required to reach one early developmental stage—the time to first heartbeat—is explained by the body size and temperature dependence of metabolic rate. Furthermore, comparisons of this stage with later developmental stages suggest that, after correcting for size and temperature, the relationship of metabolic rate to the rate of embryogenesis is approximately invariant across taxonomic groups and stages of ontogeny.

Do thermoregulatory costs limit altitude distributions of Andean forest birds

Summary Along tropical mountains, species often occupy narrow altitude ranges. Numerous biotic and abiotic factors have been proposed as determinants of altitude occupancy. We measured several aspects of thermal physiology of 215 bird species across a 2·6-km altitude gradient in the Peruvian Andes. We predicted that highland species would show adaptation to the colder high-altitude climate and that energy costs of thermoregulation might limit upslope dispersal of lowland natives. We found reductions in thermal conductance, body temperature and lower critical temperature in highland birds compared with lowland species. These combine to make highland natives more resistant to heat loss. We did not find convincing evidence that acute thermal limits or energy costs of thermoregulation constrained altitude distributions. Heat-budget models predicted low-to-moderate long-term costs at native altitudes. Costs increased for lowland natives modelled in the highland climate, but for all but a few species, costs remained within putative expenditure limits. Although we did not test heat tolerances, we measured all species at temperatures similar to the hottest air temperatures at the lowland site. There was no evidence that high lowland temperatures preclude downslope movements of highland birds. While thermal tolerances probably do not directly determine altitude occupancy by most species, the additional energy cost of thermoregulation experienced by lowland species moving upslope may trade off against investment in important life-history components such as breeding, and thereby affect altitude range limits.

NESTING OF THE YELLOW-BREASTED WARBLING-ANTBIRD (HYPOCNEMIS SUBFLAVA) WITH NOTES ON THE NESTING BIOLOGY OF THE HYPOCNEMIS CANTATOR COMPLEX

Abstract We provide the first detailed nesting biology information for the Yellow-breasted Warbling-Antbird (Hypocnemis subflava), a member of the recently split Warbling Antbird complex. We found seven pouch-shaped nests with two eggs or nestlings within Manu National Park, SE Peru. Long incubation sessions (93.7 ± 7.78 minutes, range  =  4–480 minutes, n  =  18 days) were untaken by both parents and high diurnal nest attentiveness (% of time on the nest) averaged 85.8 ± 1.4% (n  =  16) as a result of taking fewer short foraging trips (6.3 ± 0.6 trips/day, range  =  3–11; n  =  14) that lasted 16.19 ± 1.78 min (range  =  1–91; n  =  18). Incubation behavior produced an average inner nest temperature of 32.3 ± 0.24 °C (n  =  15 days) and average egg temperature of 36.4 ± 0.09 °C (n  =  3). Individual nests at different elevations exhibit differences in incubation behavior. The nestling period was 11 days (n  =  1) and both parents brooded and fed the nestlings. Nest shape, location, and composition were similar to other species in the complex, but egg coloration was variable among species.

DENSITY AND NATURAL HISTORY OF THE SICKLE-WINGED GUAN (CHAMAEPETES GOUDOTII) IN THE CENTRAL ANDES, COLOMBIA

Abstract The basic ecology of most of the Andean guans is poorly known. However, knowledge of the natural history of members of Cracidae has increased in the last decade, but most studies involve lowland species. We present basic natural history data for the Sickle-winged Guan (Chamaepetes goudotii) on the western slope of the Central Range of the Andes, Colombia. The density estimate for the Sickle-winged Guan in the study area was 13.7 individuals/km2 and the mean (± SD) group size was 1.5 ± 0.76 individuals. These groups used all forest strata but usually foraged in the middle stratum (8.6 ± 6.1 m). The diet consisted of fruits (84.5%), flowers (3.9%), leaves (5.8%), and invertebrates (5.8%). We observed wing-drumming displays, nests, and fledglings from January through June. We discuss the ability of the Sickle-winged Guan to colonize and establish populations in restored habitats.