Dumetella Research Articles

Host-seeking activity and avian host preferences of mosquitoes associated with West Nile virus transmission in the northeastern U.S.A.

Mosquito host-seeking activity was studied using a custom-designed trap to explore: (1) at which time interval of the night adult mosquito abatement would be most effective, and (2) if there exists an avian-specific host-seeking preference. Overnight trials using traps baited with dry ice showed that Aedes taeniorhynchus (Wiedemann) was most active at dusk and was then captured throughout the night. In contrast, Culex spp. (Cx. pipiens (Linnaeus) and Cx. restuans (Theobald) delayed most activity until about two h after dusk and were then captured through the night. This pattern suggests that management activities directed at adult Culex spp. would be most effective if initiated well after sunset. Mosquito capture rates in traps baited with birds in net bags were significantly greater than those with empty net bags, indicating that mosquitoes were attracted to the birds and not incidentally being sucked in by the custom trap's strong fan motor (Wilcoxon matched-pairs signed-ranks test, n=24, t=30, p<0.05). Regression analysis showed that bird weight influenced mosquito attraction (r2=0.21, p=0.02). Trials with paired traps that contained different native bird species showed that Gray Catbirds, Dumatella carolinensis, attracted more mosquitoes than the heavier Northern Cardinals, Cardinalis cardinalis (paired samples t-test, t=2.58, df=7, p=0.04). However, attractiveness did not differ substantially among bird species, and Gray Catbirds did not attract more mosquitoes than all other birds combined as a group. American Robins, Turdus migratorius (n=4) were comparable in attractiveness to other bird species, but not enough American Robins were captured for a comprehensive study of mosquito avian preference.

Test of Recrudescence Hypothesis for Overwintering of West Nile Virus in Gray Catbirds

West Nile virus is a pathogen of concern for both human and wildlife health. Although many aspects of the ecology of West Nile virus are well understood, the mechanisms by which this and similar mosquito-borne viruses overwinter and become reinitiated each spring in temperate regions is not known. A thorough understanding of this mechanism is crucial to risk assessment and development of control strategies. One of the hypotheses to explain the mechanism by which this virus persists from year to year is the spring recrudescence of latent virus in avian reservoir hosts. Stress-related immunosuppression is implicated in the recrudescence of latent viruses in birds. We tested the spring recrudescence hypothesis in a controlled laboratory experiment using hatching-year gray catbirds (Dumatella carolinensis) captured in northern Ohio (July–August 2006). Catbirds (n = 60) were experimentally infected (September 2006) and later examined for the effects of immunosuppression through exogenous hormones and artificially induced migratory disposition. We found no effect of either testosterone or migratory behavior on infection status in any of the treatment birds. Moreover, we detected no viral RNA in the kidney, spleen, brain, or liver upon necropsy at 24 wk postinfection.

Test of Recrudescence Hypothesis for Overwintering of West Nile Virus in Gray Catbirds

West Nile virus is a pathogen of concern for both human and wildlife health. Although many aspects of the ecology of West Nile virus are well understood, the mechanisms by which this and similar mosquito-borne viruses overwinter and become reinitiated each spring in temperate regions is not known. A thorough understanding of this mechanism is crucial to risk assessment and development of control strategies. One of the hypotheses to explain the mechanism by which this virus persists from year to year is the spring recrudescence of latent virus in avian reservoir hosts. Stress-related immunosuppression is implicated in the recrudescence of latent viruses in birds. We tested the spring recrudescence hypothesis in a controlled laboratory experiment using hatching-year gray catbirds (Dumatella carolinensis) captured in northern Ohio (July-August 2006). Catbirds (n = 60) were experimentally infected (September 2006) and later examined for the effects of immunosuppression through exogenous hormones and artificially induced migratory disposition. We found no effect of either testosterone or migratory behavior on infection status in any of the treatment birds. Moreover, we detected no viral RNA in the kidney, spleen, brain, or liver upon necropsy at 24 wk postinfection.

Effects of invasive woody plants on avian nest site selection and nesting success in shrublands

AbstractExotic, invasive plants are a growing conservation problem. Birds frequently use invasive plants as nest substrates, but effects of invasives on avian nesting success have been equivocal in past studies. In 2004 and 2005, we assessed effects of invasive woody plants on avian nest‐site selection and nesting success in western Massachusetts shrublands. At the nest scale, we tested the effects of invasive versus native substrates on nesting success as well as differences among individual invasive species. At the patch scale, we tested effects of invasive prevalence on nesting success in natives and invasives. We found that, as a whole, shrubland birds preferred invasive substrates. Of two species sufficiently abundant for individual analysis, gray catbirds Dumetella carolinensis preferred invasive substrates, but chestnut‐sided warblers Dendroica pensylvanica showed no preference for natives or invasives. At the nest scale, nests of gray catbirds placed in invasive substrates were more successful than those in natives. Chestnut‐sided warblers and all species combined, however, had equal nest success in invasives and natives. We found no differences in nest success for nests in different species of invasive substrates or in invasive substrates with and without thorns. At the scale of the patch, nest success in invasive substrates increased with the prevalence of invasives on a site. Nest success in native plants did not change with invasive prevalence. We attribute this finding to the tendency for thickets of invasive plants to be larger on sites with more invasive cover. These findings illustrate the complex interaction of different factors that can determine how invasive plants affect avian nesting success. We conclude that control of invasive woody plants should be neutral for most shrubland birds.

Short-chain carboxylic acids from gray catbird (Dumetella carolinensis) uropygial secretions vary with testosterone levels and photoperiod

The uropygial gland of birds produces secretions that are important in maintaining the health and structural integrity of feathers. Non-volatile components of uropygial secretions are believed to serve a number of functions including waterproofing and conditioning the feathers. Volatile components have been characterized in fewer species, but are particularly interesting because of their potential importance in olfactory interactions within and across species. We used solid-phase microextraction headspace sampling with gas chromatography-mass spectrometry to detect and identify volatiles in uropygial secretions of gray catbirds (Dumetella carolinensis), a North American migratory bird. We consistently detected the following carboxylic acids: acetic, propanoic, 2-methylpropanoic, butanoic, and 3-methylbutanoic. We tested for the effect of lengthened photoperiod and/or exogenous testosterone on volatile signal strength and found a negative effect of lengthened photoperiod on the signal strength of propanoic, 2-methylpropanoic, and butanoic acids, suggesting a trade-off between their production and heightened night-time activity associated with lengthened photoperiod. Signal strength of propanoic and 2-methylpropanoic acids was lower in birds treated with exogenous testosterone than in birds treated with placebos. Sex did not affect signal strength of any of the volatile compounds.

Repeatability of hematocrits and body mass of Gray Catbirds

ABSTRACT Hematocrits may provide information about the physiological condition of birds, but, to be a useful measure, information is needed concerning how hematocrits vary among individuals and over time. We examined the repeatability of hematocrits in a population of Gray Catbirds (Dumetella carolinensis) in Pennsylvania at several time scales and also examined the repeatability of body mass, another measure commonly used as an indicator of condition. Both hematocrit (r= 0.64) and mass (r= 0.65) were repeatable (P < 0.01) for first captures between years and between first and second captures within a year (r= 0.41 and r= 0.50, respectively; P < 0.01), but not repeatable (P > 0.05) between captures in different months within a year (r= 0.11 for both). Repeatability of both measures differed by sex and age. Females exhibited repeatability of hematocrit and body mass only between years, while male hematocrits were repeatable between years and between first and second captures within a season. Male mass was repeatable for all time periods. Hematocrits of younger birds were repeatable between captures within a season and their body mass was repeatable between months and weeks while hematocrits of older birds were not repeatable and their body mass was repeatable only between captures in a season. Our results indicate that hematocrits and body mass had similar repeatability coefficients overall, but that hematocrits of Gray Catbirds were a consistent trait of individuals only across years. Because repeatability between captures and months depended on sex and age, we conclude that the hematocrit is a useful measure of individual performance only in limited circumstances. El hematocrito podría proveer información sobre la condición física de las aves pero para ser una medida útil se necesita información sobre como el hematocrito varia entre individuos y a través del tiempo. Examinamos la repetibilidad del hematocrito en una población de Dumetella carolinensis en Pennsylvania durante diferentes escalas temporales. También examinamos la repetibilidad del peso corporal, otra medida comúnmente usada como indicador de la condición del individuo. El hematocrito (r= 0.64) y el peso corporal (r= 0.65) eran repetibles (P < 0.01) para las primeras capturas entre años y entre la primera y segunda captura dentro del año (r= 0.41 y r= 0.50, respectivamente; P < 0.01), pero no eran repetibles (P > 0.05) entre capturas realizadas en diferentes meses dentro del año (r= 0.11 para los dos). La repetibilidad de las dos medidas difiere por sexo y edad. Las hembras se caracterizaron por tener repetibilidad del hematocrito y del peso corporal solo entre años, mientras que el hematocrito de los machos era repetible entre años y entre la primera y segunda captura dentro de la temporada. El peso corporal de los machos era repetible durante todos los periodos a través del tiempo. El hematocrito de las aves mas jóvenes era repetible entre capturas dentro de la temporada y su peso corporal era repetible entre meses y semanas, mientras que el hematocrito de las aves mayores no era repetible y su peso corporal era repetible solo entre capturas dentro de la temporada. Nuestros resultados indican que los hematocritos y el peso corporal en general tuvieron coeficientes de repetibilidad similares, pero que los hematocritos de D. carolinensis eran un rasgo consistente de los individuos solo entre años. Por la razón que la repetibilidad entre capturas y meses dependía del sexo y edad, concluimos que el hematocrito es una medida útil del performance individual solo en circunstancias limitadas.

Arrival timing and hematological parameters in Gray Catbirds (Dumetella carolinensis)

Early arrival at the breeding grounds for migratory birds is associated with greater reproductive success. According to the condition-dependent arrival hypothesis, only those individuals in superior physiological condition are able to bear the costs (e.g., poor environmental conditions, limited food availability) of early arrival. Condition has usually been measured in terms of energy reserves or mass but other physiological measures of condition such as hematocrit and immune function have been gaining attention. We examined several measures of condition and their association with date of first capture in Gray Catbirds (Dumetella carolinensis) arriving at breeding grounds in northeastern Pennsylvania. Earlier arrivals had higher hematocrit and H/L ratios and lower lymphocyte counts. Arrival date was also negatively associated with fat score. Fat score was positively related to hematocrit, total number of leukocytes, and number of lymphocytes, but the other hematological parameters were not associated with traditional measures of condition (keel score, fat score, or a body condition index). Our results provide some support for the condition-dependent arrival hypothesis and suggest that there may be immunological differences between early- and late-arriving birds.

Prevalence of West Nile Virus in Migratory Birds during Spring and Fall Migration

To investigate the role of migratory birds in the dissemination of West Nile virus (WNV), we measured the prevalence of infectious WNV and specific WNV neutralizing antibodies in birds, principally Passeriformes, during spring and fall migrations in the Atlantic and Mississippi flyways from 2001-2003. Blood samples were obtained from 13,403 birds, representing 133 species. Specific WNV neutralizing antibody was detected in 254 resident and migratory birds, representing 39 species, and was most commonly detected in northern cardinals (Cardinalis cardinalis) (9.8%, N = 762) and gray catbirds (Dumetella carolinensis) (3.2%, N = 3188). West Nile virus viremias were detected in 19 birds, including 8 gray catbirds, and only during the fall migratory period. These results provide additional evidence that migratory birds may have been a principal agent for the spread of WNV in North America and provide data on the occurrence of WNV in a variety of bird species.

Avian kleptoparasitism of the digger wasp Sphex pensylvanicus

AbstractKleptoparasitism (one organism stealing prey from another) is especially common in birds. Avian kleptoparasites should be especially likely to target insects such as digger wasps (Hymenoptera: Sphecidae) that occur in large aggregations and repeatedly deliver large prey to the same nesting site. We document kleptoparasitism of digger wasps (Sphex pensylvanicus L.) by sparrows (Passer domesticus (L.)) and catbirds (Dumetella carolinensis (L.)). During summer 2008, we observed 697 wasp provisioning attempts (return of a prey-laden wasp to a marked nesting site) in a mown field. One-third (244/697) of attempts were intercepted by birds, primarily sparrows, which increased their hourly total number and hourly number of successful attacks per capita. Wasps maintained a consistent rate of successful provisioning attempts but may not have been able to do so indefinitely. Energetic costs related to kleptoparasitism may exert strong selection pressures on affected digger wasps.

Testing the role of sensory systems in the migratory heading of a songbird

The identification of the sensory cues and mechanisms by which migratory birds are able to reach the same breeding and wintering grounds year after year has eluded biologists despite more than 50 years of intensive study. While a number of environmental cues have been proposed to play a role in the navigation of birds, arguments still persist about which cues are essential for the experience based navigation shown by adult migrants. To date, few studies have tested the sensory basis of navigational cues used during actual migration in the wild: mainly laboratory based studies or homing during the non-migratory season have been used to investigate this behaviour. Here we tested the role of olfactory and magnetic cues in the migration of the catbird (Dumetella carolinensis) by radio tracking the migration of birds with sensory manipulations during their actual migratory flights. Our data suggest that adult birds treated with zinc sulphate to produce anosmia were unable to show the same orientation as control adults, and instead reverted to a direction similar to that shown by juveniles making their first migration. The magnetic manipulation had no effect on the orientation of either adults or juveniles. These results allow us to propose that the olfactory sense may play a role in experience based migration in adult catbirds. While the olfactory sense has been shown to play a role in the homing of pigeons and other birds, this is the first time it has been implicated in migratory orientation.

Using stable isotopes to track frugivory in migratory passerines

Several species of North American migratory songbirds undergo seasonal diet shifts from insects to fruits, but this phenomenon is poorly quantified. Measurement of naturally occurring stable isotopes of carbon (δ13C) and nitrogen (δ15N) are linked to sources of diets and trophic level, respectively. We used stable carbon (δ13C) and nitrogen (δ15N) isotope analyses of blood and claw tissues of 16 species of migratory songbirds to evaluate the timing and extent of frugivory over different periods. Species differed considerably in their tissue δ15N values, but we found poor isotopic segregation of species according to our a priori classifications as insectivores or omnivores. Season accounted for considerable variance in tissue δ15N values. However, only American Robin ( Turdus migratorius L., 1766), Northern Oriole ( Icterus galbula (L., 1758)), Gray Catbird ( Dumetella carolinensis (L., 1766)), Least Flycatcher ( Empidonax minimus (W.M. Baird and S.F. Baird, 1843)), and Warbling Vireo ( Vireo gilvus (Vieillot, 1808)) showed expected decrease in winter-grown tissue δ15N values compared with those grown in late summer. This indicates either that our a priori guild associations were incorrect and (or) that using stable isotopes to track frugivory at continental scales is problematic. We recommend that the isotope technique be used to track frugivory only in well-constrained systems where food-web δ15N follows reliable and understood trophic enrichment patterns.

Short communication: Absence of protandry in a population of Gray Catbirds Dumetella carolinensis

Sex-based differential arrival on the breeding grounds at the completion of migration has been poorly studied in monochromatic and monomorphic species because individuals are difficult to sex without recapture or molecular tests. We examined sex-based arrival timing to the breeding grounds of the Gray Catbird Dumetella carolinensis, a monochromatic species. We also examined differences in size and arrival by age as these are well documented to affect arrival timing. Older birds were larger than younger birds, and older males were larger than older females. Older birds arrived back on the breeding grounds earlier than younger birds, as documented in many species, but males did not precede females. Our results provide evidence of sexual size dimorphism in Catbirds and add to a growing body of information on arrival timing in monochromatic species. Differences in intensity of sex-based competition for breeding resources are hypothesized as the primary selective force for one sex to precede the other to the breeding grounds (Kokko 1999, Kokko et al. 2006). Typically, males arrive at the breeding grounds in advance of females (Morbey & Ydenberg 2001), a phenomenon known as protandry (Rubolini et al. 2004). This is because males are thought to experience more intensive selective pressure for acquiring territories or other resources for attracting a mate than females (but see Kokko et al. 2006 for a discussion of why females may also be under selection pressure for earlier arrival to compete for resources or mates). Furthermore, comparative studies suggest that the extent of sexual selection experienced by males, as evidenced by the degree of sexual dichromatism (Moller & Birkhead 1994, Owens & Hartley 1998), sexual size dimorphism (Owens & Hartley 1998, Dunn et al. 2001), polygyny or rate of extra-pair paternity (Coppack et al. 2006), affects the degree of protandry. While protandry is well documented in dimorphic species (Rubolini et al. 2004), little is known about arrival dates by sex in monomorphic or monochromatic species (Rubolini et al. 2004, Edwards & Forbes 2007, Newton 2008). The primary reason for this is the difficulty in sexing individuals upon arrival at the migratory destination. Moreover, the limited studies to date have produced equivocal results. For example, male Spotted Flycatchers Muscicapa striata preceded females during passage on the island of Ventotene, Italy, (Mabey 2002), and male White-throated Sparrows Zonotrichia albicollis and Least Flycatchers Empidonax minimus preceded females during spring migration at Long Point Observatory, Ontario, Canada (Mills 2005). In contrast, Edwards and Forbes (2007) presented evidence that Song Sparrows Melospiza melodia did not exhibit protandry upon arrival at breeding grounds in Ontario. Our research on arrival and breeding in the Gray Catbird afforded us the opportunity to assess arrival timing by sex and age in a songbird migrant described as monochromatic and monomorphic (Cimprich & Moore 1995). One advantage of our study is that we captured birds both during the arrival period and throughout the breeding season, permitting us to determine an individual’s sex and relate it back to when it arrived at breeding grounds in northeastern Pennsylvania. Although there are several hypotheses regarding differences (or lack of differences) in arrival timing between the sexes (Morbey & Ydenberg 2001) here we focus on assessing whether catbirds are indeed monomorphic and whether they exhibit protandry.

Video Recording Reveals the Method of Ejection of Brown-Headed Cowbird Eggs and No Cost in American Robins and Gray Catbirds

Abstract. Despite the importance of knowing the method and cost of ejection in understanding the persistence of brood parasitism, anecdotal records of witnessed ejections of real Brownheaded Cowbird (Molothrus ater) eggs exist for only eight of ∼30 ejecter species. The probability of a host damaging its own egg while ejecting a parasite's egg is thought to be lower for hosts that grasp-eject, but grasp-ejection is an option only for hosts with appropriate bills. For hosts incapable of grasp-ejection, the cost of puncture-ejection may render acceptance adaptive. We video-recorded 12 ejections of real cowbird eggs by American Robins (Turdus migratorius) and 17 by Gray Catbirds (Dumetella carolinensis). With no damage to their own eggs, robins graspejected all cowbird eggs, whereas catbirds grasp-ejected 14 eggs and puncture-ejected three eggs. Our study revealed that a few species use a mixture of ejection methods and even large species may puncture-eject with little cost.

Winter Site Fidelity and Over-winter Site Persistence of Passerines in Florida

Many species of temperate migrant birds are abundant in winter in the southeastern United States, but little is known about fidelity of migratory species to wintering areas. Mist netting was conducted at Rock Springs Run State Reserve in Orange County, Florida during the non-breeding season from 1997 to 2002. We quantify the first records of winter site fidelity for Gray Catbird (Dumetella carolinensis), House Wren (Troglodytes aedon), and Orange-crowned Warbler (Vermivora celata). We also document the first known winter returns of Blue-headed Vireo (Vireo solitarius) and Ovenbird (Seiurus aurocapilla) in temperate winter areas. Many site faithful birds exhibited over-winter site persistence by being recaptured many times throughout the winter (over 4 weeks), suggesting these birds are site faithful within and between years. Patterns of returns and over-winter site persistence followed trends expected from life history characteristics for most species.

TESTING AN ASSUMPTION OF THE SEXUAL-SIGNALING HYPOTHESIS: DOES BLUE-GREEN EGG COLOR REFLECT MATERNAL ANTIOXIDANT CAPACITY?

Abstract The presence of blue-green egg pigmentation has puzzled naturalists for more than 100 years. One hypothesis on the function of this pigmentation proposes that blue-green egg chroma signals female quality and that males respond to this signal by increased provisioning to presumably higher-quality clutches. The hypothesized mechanism is that blue-green egg color signals female antioxidant capacity, because the eggshell pigment responsible for blue-green coloration, biliverdin, has antioxidant properties in the mother. Our study is the first to examine this mechanism, which is critical to this hypothesis. We found that female Gray Catbirds with higher total antioxidant capacity laid eggs with higher blue-green chroma. In addition, we found that males provided more care to nestlings from clutches with higher average blue-green egg chroma. This shows an intriguing potential link between female antioxidant capacity and blue-green egg chroma. Interpreting the variation in females' antioxidant capacity w...

Stress, Metabolism, and Antioxidants in Two Wild Passerine Bird Species

Antioxidants protect against free-radical damage, and free radicals, in turn, are thought to underlie aging. Thus, measuring antioxidants may aid field ecologists in understanding the physiological mechanisms that underlie life-history trade-offs. Antioxidant levels are known to vary markedly in response to the stress of capture in many birds. These changes in antioxidants could result from regulation (e.g., by stress-related hormones) or consumption (e.g., by an increase in free radicals due to increased metabolic rate). Here we experimentally test the effect of increased metabolic rate on circulating antioxidant and corticosterone concentrations in two wild passerine bird species, house sparrows (Passer domesticus) and gray catbirds (Dumetella carolinensis). We increased metabolic rate via exposure to low ambient temperatures overnight in captivity and measured circulating antioxidant capacity, uric acid, corticosterone, and oxygen consumption in cold-exposed and control individuals. Both species showed increases rather than decreases in all antioxidant parameters overnight, contradicting a consumption-by-energy-expenditure hypothesis. Both positive and negative correlations between antioxidant response and corticosterone response were occasionally but not consistently present, refuting a generalized regulation-by-corticosterone hypothesis. High baseline uric acid predicted diminished response of corticosterone and all antioxidants. Thus, high uric acid may reflect recent stress, poor condition, or a compensatory response. Relationships among metabolic rate, antioxidants, and corticosterone differed qualitatively between the species.

Autumn Stopover Near The Gulf Of Honduras By Nearctic-Neotropic Migrants

Abstract The southeastern Yucatan Peninsula hosts high numbers of transient Nearctic-Neotropic migrants during autumn migration, but the importance of this region during migratory stopover has not been addressed. We studied autumn stopover body mass gains among passerine migrants in tropical lowland forest 20 km inland from the Gulf of Honduras. Most individuals captured had some subcutaneous fat. Ten of 15 taxa with sufficient sample sizes had significant positive diel (24 hr) gains in a body condition index. Estimates of net mass gains in these 10 taxa suggested they all were depositing fat; average individuals in four of these taxa were depositing sufficient fuel to undertake an entire night of migration after only 1 day of fattening: Empidonax spp., Red-eyed Vireo (Vireo olivaceus), Gray Catbird (Dumetella carolinensis), and Northern Waterthrush (Seiurus noveboracensis). Two (Wood Thrush [Hylocichla mustelina] and Common Yellowthroat [Geothlypis trichas]) of the four species apparently not gaining mas...

Long-Term Effects of Wastewater Irrigation on Habitat and a Bird Community in Central Pennsylvania

We studied the possible long-term (1987 vs. 2003–2004) effects of wastewater irrigation of forests to habitat and a songbird community in central Pennsylvania. The study site, Toftrees, is a wastewater-irrigated deciduous forest interspersed with agriculture grasslands and crop fields that receives ∼260 cm of wastewater annually. Habitat variables were quantified within 15 random 0.04-ha circular plots in 2003 and 20 random plots in 1987. We conducted bird surveys twice weekly during 2003 and mist-netted birds for 1,250 hrs during 2004. Surveys and mist-netting efforts paralleled those conducted in 1987. A major decline in density of understory trees and short shrubs was noted between 1987 and 2003; in contrast, cover of herbaceous vegetation and density of tall shrubs dramatically increased. Ground-shrub foraging bird species and two mid-canopy foragers, Red-eyed Vireo (Vireo olivaceus) and Eastern Wood-Pewee (Contopus virens), declined from 1987 to 2003–2004. Conversely, Gray Catbirds (Dumetella carolinensis) increased dramatically over this time period.

OBSERVATION OF A NORTHERN CARDINAL NEST REUSED BY A GRAY CATBIRD IN THE SAME SEASON

Abstract We report a Gray Catbird (Dumetella carolinensis) reusing a Northern Cardinal (Cardinalis cardinalis) nest in the same breeding season. The Northern Cardinal nest failed during incubation on 19 June 2006, but the Gray Catbird nest was successful, fledging three young on 31 July 2006. Nest site availability does not appear to be the reason for reuse of the nest. Time constraints late in the breeding season may result in use of old nests.

Yellow-breasted Chat and Gray Catbird Productivity in a Fragmented Western Riparian System

We studied the effects of habitat fragmentation on productivity of Yellow-breasted Chat (Icteria virens) and Gray Catbird (Dumetella carolinensis) in southern British Columbia in a western riparian ecosystem. Nesting dates were later in isolated habitat patches than in continuous habitat patches for both species. We found no direct evidence that habitat fragmentation decreased productivity in either species. Average fecundity did not significantly differ between continuous (2.54 fledglings for Gray Catbird; 1.78 and 1.67 fledglings for Yellow-breasted Chat in 2002 and 2003, respectively) and isolated sites (1.33 fledglings for Gray Catbird; 1.78 and 0.87 fledglings for Yellow-breasted Chat in 2002 and 2003, respectively). Territory size, as measured by mapping perch locations for breeding adults, was smaller for Yellow-breasted Chats breeding in the Okanagan Valley (0.25 ha) than for chats in mid and high-density southern populations. However, overall fecundity and nest success were similar to more southerly populations. These results suggest that both species can persist in a relatively fragmented ecosystem.