Northern Mockingbirds Mimus Polyglottos Research Articles

A cross-sectional field study of fall song in Northern Mockingbirds Mimus polyglottos

Studies of the acoustic structure of song in young birds have proven valuable at helping us understand song development, but nearly all existing studies have been performed on non-mimicking songbirds. We conducted a cross-sectional field study of song development in a prominent vocal mimic, the northern mockingbird, by comparing the fall songs of hatch-year vs. after-hatch-year birds. Although sample sizes of hatch-year birds were small, the data suggest a developmental trajectory in which both song stereotypy and the frequency of vocal mimicry increase with age. Thus, the acoustic structure of fall song may provide a reliable indicator of a bird’s age and performance.

Sub-lethal exposure to lead is associated with heightened aggression in an urban songbird

Many urban areas have elevated soil lead concentrations due to prior large-scale use of lead in products such as paint and automobile gasoline. This presents a potential problem for the growing numbers of wildlife living in urbanized areas as lead exposure is known to affect multiple physiological systems, including the nervous system, in vertebrate species. In humans and laboratory animals, low-level lead exposure is associated with neurological impairment, but less is known about how lead may affect the behavior of urban wildlife. We focused on the Northern Mockingbird Mimus polyglottos, a common, omnivorous North American songbird, to gain insights into how lead may affect the physiology and behavior of urban wildlife. We predicted that birds living in neighborhoods with high soil lead concentrations would (a) exhibit elevated lead concentrations in their blood and feathers, (b) exhibit lower body condition, (c) exhibit less diverse and consistent vocal repertoires, and (d) behave more aggressively during simulated conspecific territorial intrusions compared to birds living in neighborhoods with lower soil lead concentrations. Controlling for other habitat differences, we found that birds from areas of high soil lead had elevated lead concentrations in blood and feathers, but found no differences in body condition or vocal repertoires. However, birds from high lead areas responded more aggressively during simulated intrusions. These findings indicate that sub-lethal lead exposure may be common among wildlife living in urban areas, and that this exposure is associated with increased aggression. Better understanding of the extent of the relationship between lead exposure and aggression and the consequences this could have for survival and reproduction of wild animals are clear priorities for future work in this and other urban ecosystems.

An Acoustic Comparison of Mimetic and Non-Mimetic Song in Northern MockingbirdsMimus polyglottos

In this descriptive study we performed an acoustic comparison of mimetic and non-mimetic song in a highly conspicuous mimic, the Northern Mockingbird Mimus polyglottos. Using automated acoustic software we measured 13 acoustic features from the mimetic and non-mimetic song of 13, free-living, male mockingbirds recorded during the breeding season. We found that when mockingbirds mimic they extend the maximum frequency of their song by over 600 Hz, which increases the frequency bandwidth by 42%. These differences might reflect female preference for the acoustic features present in mimetic song, or they might represent an artefact of which particular acoustic models are imitated by mockingbirds when developing a mimetic repertoire.

Seasonal patterns of vocal mimicry in northern mockingbirds Mimus polyglottos

Many aspects of birdsong vary seasonally, but we know almost nothing about seasonal variation in vocal mimicry, a conspicuous feature of the songs of 15–20% of bird species. I sampled spontaneous song from nine, free‐living, male northern mockingbirds Mimus polyglottos four times during the calendar year – three times during the breeding season, and once during the non‐breeding season. Results showed that mockingbirds did not mimic summer migrants significantly more during any sampling period. Results also showed significant differences across sampling periods in the frequency, but not diversity, of mimicry. Frequency of mimicry was highest in late spring (61.3%) and lowest during the non‐breeding season (48.3%), suggesting mimicry might play a role in reproductive stimulation of multiple‐brooded females. Because mockingbirds mimicked summer migrants throughout the year, regardless of whether migrants were present, mimicry is unlikely to facilitate interspecies communication. Seasonal patterns also suggest that females might be attracted to a high frequency of mimicry, but not to a high diversity of mimicry. I argue that observational studies of seasonal variation in additional mimics could provide key insights into the functional role of vocal mimicry.

Ecology of the Cooper's Hawk in North Florida

AbstractWe studied adult Cooper's hawks Accipiter cooperii on two study areas in north Florida from 1995 to 2001, an area dominated by large plantations managed for northern bobwhite Colinus virginianus and an area of mixed farmland and woods with no direct bobwhite management. We monitored 76 Cooper's hawk nesting attempts at 31 discrete nest areas, and radio-tagged 19 breeding males and 30 breeding females that we radio-tracked for up to 5 y. Nesting density (565 to 1,494 ha per occupied nest area) was comparable but productivity (1.8 and 2.8 young fledged per occupied and successful nest area, respectively) was lower than for the species elsewhere. Prey may have been more limiting than in other areas studied because chipmunks Tamias striatus, an important prey elsewhere, were absent. Annual Cooper's hawk survival averaged 84% for males and 81% for females, except in 1998 when survival was substantially lower. Average annual home-range size for male Cooper's hawks was 15.3 km2 inclusive of one nesting area. Female annual ranges averaged 30.3 km2, and included from three to nine nesting areas. Daily space use was similar between the sexes, but females had separate breeding and nonbreeding ranges whereas males were sedentary. Females used the same nonbreeding areas among years, but switched nesting areas 68% of the time compared with only 17% for males. Birds comprised 88% of the breeding and 98% of the nonbreeding season diet of Cooper's hawks by frequency. Important prey species all year were mourning doves Zenaida macroura, blue jays Cyanocitta cristata, and northern bobwhite; during summer, cattle egrets Bubulcus ibis, northern mockingbirds Mimus polyglottos and northern cardinals Cardinalis cardinalis were also important; and during autumn and winter, killdeer Charadrius vociferus, yellow-billed cuckoos Coccyzus americanus, and chickens were important. Female Cooper's hawks took larger prey than males; females were responsible for most cattle egret and chicken kills; whereas, males took most blue jays, killdeer, northern mockingbirds, and northern cardinals. Of avian prey brought to nests, 64% were nestling birds. Most adult male Cooper's hawks were adept at raiding bird nest boxes. Male Cooper's hawks captured 85% of the prey fed to nestlings. Female Cooper's hawks relied on males for food from early March until young were ≥12 d old, and 6 of 10 breeding females monitored intensively were never observed foraging for their broods. Most prey brought to nestling Cooper's hawks was captured within 2 km of nests, and foraging effort was consistent throughout the day. During the nonbreeding season, most prey captures occurred before 0900 hours or at dusk. Northern bobwhite made up 2% of male and 6% of female Cooper's hawk prey annually by frequency; this extrapolated to 18 bobwhite/year/adult Cooper's hawk on both study areas, 59% of which were captured between November and February. Outside the breeding season, male Cooper's hawks foraged evenly over their home range whereas females tended to focus on prey concentrations. Because female Cooper's hawks were so adept at finding and exploiting prey hotspots, perhaps the best strategy for reducing predation on bobwhite is habitat management that produces an even distribution of bobwhite across the landscape.

Abundance and Diversity of Arthropods in Nests of Lark Sparrows (Chondestes grammacus)

Abstract We examined abundance and diversity of arthropods in nests of lark sparrows (Chondestes grammacus). No true ectoparasite occurred in the nests sampled (n = 69) and no ectoparasite was found on nestlings. However, 67% of nests contained non-parasitic arthropods from ≥16 families. There was no significant difference in number of arthropods per gram of nesting material or diversity (at familial to higher taxonomic order) with height of nest (ground or arboreal), date of nesting, duration of activity per nesting attempt, mean or maximum temperature of nest, and frequency of prescribed burning of the habitat, or in relation to nest-building by two species of birds (lark sparrows and northern mockingbirds Mimus polyglottos).

Are urban habitats ecological traps for a native songbird? Season‐long productivity, apparent survival, and site fidelity in urban and rural habitats

The northern mockingbird Mimus polyglottos is a native species that is more abundant in urban than non‐urban habitats (i.e. an urban‐positive species). Abundance alone, however, is not an accurate index of habitat quality because urban habitats could represent ecological traps (attractive sink habitat) for urban‐positive species. We compared mockingbird nesting productivity, apparent survival, and decision rules governing site fidelity in urban and rural habitats. If the higher abundance of mockingbirds in urban habitats is driven by higher quality urban habitat, then we predicted that productivity of urban mockingbirds would exceed the estimated source‐sink threshold and productivity of non‐urban mockingbirds. If, on the other hand, urban habitats act as ecological traps, productivity would be lower in urban habitats and would fall below the estimated source‐sink threshold. Productivity of urban pairs exceeded that of non‐urban pairs and more than offset estimated adult mortality, which makes urban habitat a likely source habitat. Apparent adult survival was higher in urban habitats than in non‐urban habitats, although this could be driven by dispersal more than mortality. Decision rules also appeared to differ between urban and non‐urban populations. Females in urban habitats with successful nests were more likely to return than those with unsuccessful nests, whereas return rates of females in nonurban habitats were unrelated to nesting success and may be more related to nesting habitat availability. We conclude that urban habitats do not act as ecological traps that lure mockingbirds into sink habitat and that increased breeding productivity contributes to their success in urban habitats.

Two-voice complexity from a single side of the syrinx in northern mockingbirdMimus polyglottosvocalizations

The diverse vocal signals of songbirds are produced by highly coordinated motor patterns of syringeal and respiratory muscles. These muscles control separate sound generators on the right and left side of the duplex vocal organ, the syrinx. Whereas most song is under active neural control, there has been a growing interest in a different class of nonlinear vocalizations consisting of frequency jumps, subharmonics, biphonation and deterministic chaos that are also present in the vocal repertoires of many vertebrates, including many birds. These nonlinear phenomena may not require active neural control, depending instead on the intrinsic nonlinear dynamics of the oscillators housed within each side of the syrinx. This study investigates the occurrence of these phenomena in the vocalizations of intact northern mockingbirds Mimus polyglottos. By monitoring respiratory pressure and airflow on each side of the syrinx, we provide the first analysis of the contribution made by each side of the syrinx to the production of nonlinear phenomena and are able to reliably discriminate two-voice vocalizations from potentially similar appearing, unilaterally produced, nonlinear events. We present the first evidence of syringeal lateralization of nonlinear dynamics during bilaterally produced chaotic calls. The occurrence of unilateral nonlinear events was not consistently correlated with fluctuations in air sac pressure or the rate of syringeal airflow. Our data support previous hypotheses for mechanical and acoustic coupling between the two sides of the syrinx. These results help lay a foundation upon which to understand the communicative functions of nonlinear phenomena.

Interspecific variation in avian blood parasites and haematology associated with urbanization in a desert habitat

Many avian species are negatively impacted by urbanization, but other species survive and prosper in urbanized areas. One factor potentially contributing to the success of some species in urban areas is the reduced presence of predators or parasite vectors in urban compared to rural areas. In addition, urban areas may provide increased food and water resources, which can enhance immune capacity to resist infection and the ability to eliminate parasites. We determined patterns of blood parasitism, body condition, and immune cell profiles in urban and rural populations of five adult male songbird species that vary in their relative abundance within urban areas. Urban birds generally exhibited less blood parasitism than rural birds. This difference was particularly evident for the urban‐adaptable Abert's towheePipilo aberti. In contrast, no difference in haemoparasitism was seen between urban and rural populations of the curve‐billed thrasherToxostoma curvirostre, a less‐urban adaptable species. In two closely related species, the curve‐billed thrasher and the northern mockingbirdMimus polyglottos, urban birds had a higher leukocyte count and a higher heterophil to lymphocyte ratio, which is often associated with chronic stress or current infection, than rural birds. Urban northern mockingbirds were in better condition than rural counterparts, but no habitat‐related differences in condition were detected for other species. Parasitic infection was correlated with body condition in only one species, the canyon towheePipilo fuscus. Parasitic infection in most species was correlated with changes in leukocyte abundance and profile. The findings suggest that interspecific differences in parasitic infection cannot be attributed entirely to differences in vector abundance or body condition. Interactions between immune function, parasite infection risk, and resource availability may contribute to determining the relative ability of certain species to adapt to cities.

Habitat requirements of the Socorro Mockingbird Mimodes graysoni

The population size of the Socorro Mockingbird Mimodes graysoni, which represents a monotypic genus endemic to Socorro Island, México, has declined dramatically within the last 40 years. Postulated causal factors include competitive exclusion by Northern Mockingbirds Mimus polyglottos, predation by feral cats and overgrazing by feral sheep. Habitat degradation looms as the primary candidate because surviving Socorro Mockingbirds live mainly in areas of the island with little apparent habitat damage, and because Northern Mockingbirds and cats both arrived on Socorro after much of the decline had occurred. Isolating key factors is difficult, however, because the present distributions of cats and Northern Mockingbirds coincide broadly with patterns of habitat degradation. To investigate habitat requirements of the endemic mockingbird in detail, we measured vegetation characteristics at localities with and without Socorro Mockingbirds, and observed their foraging behaviour. Socorro Mockingbirds occupied sites in montane regions covered with Ilex socorroensis, Guettarda insularis, Triumfetta socorrensis and Eupatorium pacificum; they were also abundant in pristine lowland forests. Socorro Mockingbirds were scarce in disturbed forests where Dodonaea viscosa has replaced the original understorey, and they were absent from low‐elevation Croton masonii scrub, even in areas with no signs of degradation. Restoration of degraded habitat could help the population of Socorro Mockingbirds grow and reoccupy more of its former range.

Developing microsatellites when they are rare: trinucleotide repeat loci in the northern mockingbird Mimus polyglottos.

The great value of microsatellite loci to population studies spurs their development. However, finding loci is difficult when microsatellites are uncommon in the genome. Because trinucleotide-repeat loci are rare in northern mockingbirds Mimus polyglottos, we sought a new method for developing a suite of loci. Here we show that a bacterio-phage cloning vector, Lambda Zap Express (Stratagene, La Jolla, CA, USA) has several features which make it suitable for this purpose. Using this vector, we made a library of 150,000 size-selected clones and screened with an AAT10 probe; 97 positives were identified. From these, 12 pairs of PCR primers were developed, nine of which amplify polymorphic loci. Certain combinations of these primer pairs enable simultaneous amplification of up to three loci.

The conservation status of the Socorro MockingbirdMimodes graysoniin 1993–1994

SummaryThe Socorro MockingbirdMimodes graysoniis endemic to Socorro Island, Mexico, and has declined dramatically in this century. Study of its population size, distribution, and structure is currently under way to help assess its conservation status. In 1993 and 1994 215 Socorro Mockingbirds were ringed; a modified Lincoln index yielded a population estimate of 353 ± 66 individuals in 1994. Most of the birds observed occupied a small region at high elevation that covered less than 10% of the island's area. Average territory size was 1.48 ± 0.71 ha,n= 11. Of the 86 birds banded in 1993 67% were adults and 33% subadults. Of the 170 birds detected in 1994, including new captures and ringed individuals from the previous year, 44% were adults and 56% subadults. In 1993 62% were male and 38% female; in 1994 56% were male and 44% were female. The sex ratio of the population was similar to that of other undisturbed Mimid populations, which argues against the possibility that cats might prey disproportionately on incubating females. Moreover, the presence of young birds in both years indicates that successful reproduction was occurring and that the population was not suffering catastrophic nest failure, as might be caused by cat predation on nestlings or fledglings. Northern MockingbirdsMimus polyglottos, which first arrived on Socorro in the 1970s, occupied mainly open areas produced by sheep grazing, which suggests that the Socorro Mockingbird is not being competitively displaced. Our observations indicate that habitat degradation by sheep is the most probable cause of the Socorro Mockingbird's decline.

Testosterone and Reproductive Adaptations in the Autumnal Territoriality of Northern Mockingbirds Mimus polyglottos

Testosterone and Reproductive Adaptations in the Autumnal Territoriality of Northern Mockingbirds Mimus polyglottos

“Replacements” of Landbird Species on Socorro Island, Mexico

Abstract The endemic dove Zenaida graysoni of Socorro Island, an oceanic island in the Pacific south of Baja California, became extirpated between 1958 and 1978, and the endemic mockingbird Mimodes graysoni diminished during the same years and was approaching extinction by 1981. The mainland Mourning Dove Z. macroura became established on Socorro between (probably) 1971 and 1978, and the mainland Northern Mockingbird Mimus polyglottos between 1978 and 1981. Superficially an instance of replacement of island endemics by mainland relatives through competitive exclusion, the case is actually more complicated. We argue that extermination of the endemics was probably caused by predation by feral cats introduced in 1957 or later. There is no evidence of any actual competition between the pairs of species, and their preferred habitats overlap only slightly. We attribute the nearly concurrent establishment of the two invading species, known to have occurred frequently as casual visitors to Socorro and other islands, largely to the provision of fresh water made available as a result of human settlement. Our data show that simple comparison of island species lists compiled at intervals is an inadequate base for theories of island species turnover.