Urban-associated habitat alteration promotes brood parasitism of Acadian Flycatchers

ABSTRACT.   High rates of brood parasitism are generally associated with agricultural landscapes, but recent evidence suggests that urbanization may also increase the likelihood of brood parasitism. I evaluated the extent to which brood parasitism by Brown-headed Cowbirds ( Molothrus ater ) was explained by differences in (1) body size of adult hosts, presumably relating to the ability to defend nest from cowbirds, (2) nest placement in substrate and relative to habitat edges, (3) habitat structure surrounding nests, (4) host density, (5) cowbird abundance, both absolute and relative to host numbers, (6) landscape composition, and (7) Julian date. From 2001 to 2006, I monitored nest fate and measured vegetation characteristics surrounding nests of Acadian Flycatcher ( Empidonax virescens ) breeding in mature riparian forests in central Ohio, USA. The likelihood that a nest would be parasitized was best explained by the number of understory stems surrounding the nest and, to a lesser extent, by the amount of urbanization in the surrounding 1-km-radius landscape. Parasitized nests were surrounded by 1.6 times more stems and nearly twice the amount of urbanization than nonparasitized nests. Numbers of understory stems were positively associated with increasing urbanization, primarily due to invasion of urban forests by Amur honeysuckle ( Lonicera maackii ). Thus, urban-associated changes in habitat characteristics around nests may be important contributors to the greater vulnerability of urban nests to brood parasitism than nests in more rural landscapes. This pattern suggests that ecological restoration, such as removing exotic shrubs, may be an effective strategy to ameliorate certain negative consequences of urbanization near wooded reserves.     

Experimental support for the role of nest predation in the evolution of brood parasitism

In 1965, Hamilton and Orians (HO) hypothesized that the starting point for the evolution of obligate interspecific brood parasitism in birds was the facultative laying of physiologically committed eggs in neighbouring active nests of con‐ and heterospecifics, following predation of a bird’s own nest during the laying stage. We tested this prediction of the HO hypothesis by using captive pairs of zebra finches (Taeniopygia guttata), a species with evidence for intraspecific parasitism both in the wild and in captivity. As predicted, in response to experimental nest removal, subjects laid eggs parasitically in simulated active conspecific nests above chance levels. Across subsequent trials, we detected both repeatability and directional change in laying patterns, with some subjects switching from parasitism to depositing eggs in the empty nest. Taken together, these results support the assumptions and predictions of the HO hypothesis, and indicate that the zebra finch is a potential model species for future behavioural and genetic studies in captive brood parasite research.     

Importance of spatial habitat structure on establishment of host defenses against brood parasitism

We used metapopulation dynamics to develop a mathematical simulationmodel for brood parasites and their hosts in order to investigatethe validity of the "spatial habitat structure hypothesis,"which states that a low level of parasite egg rejection in hostpopulations is due to the immigration of acceptor individualsfrom nonparasitized populations. In our model, we varied dispersalrate and the relative carrying capacity of host individualsin parasitized and unparasitized patches. When both the relativecarrying capacity in the parasite-free patch and the dispersalrate increase, the nonparasitized patch will provide more acceptorindividuals to the parasite-prone patch. As the relative carryingcapacity in the parasite-free patch increases, the equilibriumfrequency of rejecters both in the parasite-prone and in theparasite-free patch decreases toward zero for intermediate levelsof the dispersal rate. Although the rejecter strategy is moreadaptive than the acceptor strategy in the parasite-prone patch,large numbers of acceptors are produced in the parasite-freepatch dispersing to the parasitized patch. As the number ofindividuals in the parasite-free patch increases, parasitismrate can be maintained stable at a high equilibrium level inthe parasite-prone patch.     

The evolution of egg size in the brood parasitic cuckoos

We compared genera of nonparasitic cuckoos and two groups ofparasitic cuckoos: those raised together with host young ("nonejectors")and those in which the newly hatched cuckoo either ejects thehost eggs or chicks, or kills the host young ("ejectors"). Nonejectorsare similar to their hosts in body size and parasitize largerhosts than do ejectors, which parasitize hosts much smallerthan themselves. In both types of parasite, the cuckoo's eggtends to match the host eggs in size. To achieve this, nonejectorshave evolved a smaller egg for their body size than have nonparasiticcuckoos, and ejectors have evolved an even smaller egg. Amongejector cuckoo genera, larger cuckoos have larger eggs relativeto the eggs of their hosts, and the relationship between cuckooegg volume (mass of the newly-hatched cuckoo) and host egg volume(mass to be ejected) did not differ from that predicted by weight-liftingallometry. However, comparing among Cuculus cuckoo species,the allometric slope differed from the predicted, so it is notclear that egg size is related to the need to give the cuckoochick sufficient strength for ejection. Comparing the two mostspeciose ejector genera, Chrysococcyx cuckoos (smaller and parasitizedome-nesting hosts) lay eggs more similar in size to their host'seggs than do Cuculus cuckoos (larger and parasitize open cup–nestinghosts). Closer size-matching of host eggs in Chrysococcyx mayreflect the following: (1) selection to reduce adult body massto facilitate entry through small domed nest holes to lay, and(2) less need for a large egg, because longer incubation periodsin dome-nesting hosts allow the young cuckoo more time to growbefore it need eject host eggs.     

The evolution of brood parasitism: the role of facultative parasitism

The hypothesis that facultative brood parasitism may serve asan intermediate step in the evolutionary transition from purelyparental reproduction to obligate parasitism was investigated.The population dynamics of a host-parasite complex were computer-simulatedin a model that incorporated different intensities of parasitismand host defense and considered a simplified semelparous birdspecies living in a homogeneous habitat The individuals usetwo different breeding strategies: provide parental care orparasitize the nest of those providing parental care. Underobligate parasitism, the parasites appeared unsuccessful, drovethe host population to extinction, or coexisted with the hostin stable or oscillating proportions. The behavior of the systemdepended on both the effectiveness of the parasite and the defenseof the host. Under facultative parasitism (making the best ofa bad job), the parasites reduced host numbers but did not reducethe population size below the number of breeding sites. Thus,facultative parasitism provides a better opportunity for thedevelopment of defense in the host. The population of a hostthat shows a certain level of defense can be more successfullyinvaded by obligate parasites so that stable coexistence ofhosts and parasites is possible.     

Piping plover habitat selection and nest success on natural,managed, and engineered sandbars

Loss of breeding habitat and nest predation have contributed to the decline of many shorebird species. The United States Army Corps of Engineers (USACE) initiated a piping plover (Charadrius melodus) habitat creation and augmentation program on the Missouri River in the summer of 2004. The USACE increased unvegetated sandbar habitat by depositing dredged material (engineered sandbars) and by clearing vegetation from existing sandbars (managed sandbars). We evaluated the effects of this increase in nesting and foraging habitat on habitat selection and nest daily survival rate (DSR) of piping plovers on Lewis and Clark Lake and the Gavins Point Reach of the Missouri River from 2005 to 2007 (n = 623 nests). Piping plovers selected engineered sandbars more often than expected based on area and selected natural and managed habitats less than expected based on area. Daily survival rate on engineered sandbars was significantly higher than on natural or managed sandbars (log odds: 2.50, 95% CI: 1.05–5.94). Thus, plovers' habitat selection may have increased their nesting success. Our results suggest that habitat augmentation may stave off declines in piping plover populations limited by insufficient habitat and low nesting success. © 2011 The Wildlife Society.     

Individual patterns of habitat and nest-site use by hosts promote transgenerational transmission of avian brood parasitism status

Brood parasitic birds impose variable fitness costs upon their hosts by causing the partial or complete loss of the hosts' own brood. Growing evidence from multiple avian host-parasite taxa indicates that exposure of individual hosts to parasitism is not necessarily random and varies with habitat use, nest-site selection, age or other phenotypic attributes. For instance, nonrandom patterns of brood parasitism had similar evolutionary consequences to those of limited horizontal transmission of parasites and pathogens across space and time and altered the dynamics of both population productivity and co-evolutionary interactions of hosts and parasites. We report that brood parasitism status of hosts of brown-headed cowbirds Molothrus ater is also transmitted across generations in individually colour-banded female prothonotary warblers Protonotaria citrea. Warbler daughters were more likely to share their mothers' parasitism status when showing natal philopatry at the scale of habitat patch. Females never bred in their natal nestboxes but daughters of parasitized mothers had shorter natal dispersal distances than daughters of nonparasitized mothers. Daughters of parasitized mothers were more likely to use nestboxes that had been parasitized by cowbirds in both the previous and current years. Although difficult to document in avian systems, different propensities of vertical transmission of parasitism status within host lineages will have critical implications both for the evolution of parasite tolerance in hosts and, if found to be mediated by lineages of parasites themselves, for the difference in virulence between such extremes as the nestmate-tolerant and nestmate-eliminator strategies of different avian brood parasite species.     

Nest success of northern bobwhite on managed and unmanaged landscapes in southeast Iowa

Range-wide declines in northern bobwhite populations (Colinus virginianus) have been attributed to concomitant loss of breeding habitat. Bobwhite management efforts to restore this habitat resource can be informed by empirical studies of associations between breeding success and multi-scale habitat attributes. We compared bobwhite nest success in 2 southern Iowa landscapes as a function of microhabitat and landscape composition. Lake Sugema Fish and Wildlife Area (LSWA) was managed to promote bobwhite recruitment, and Harrisburg Township (HT) was an adjacent landscape dominated by private agricultural production. Survival rate modeling based on telemetry data provided evidence for age-specific daily nest survival rate. Daily survival rates decreased as nest age increased, but the decline was more severe at HT. Nest survival at LSWA (S = 0.495, SE = 0.103) was nearly twice that on HT (S = 0.277, SE = 0.072). We found no evidence that habitat composition or spatial attributes within 210 m of a nest site significantly influenced nest success. Forb canopy at the nest site had a positive influence on nest success at HT but not at LSWA. We suggest nesting habitat with greater forb canopy cover will increase the opportunity for nesting success in landscapes with limited nesting habitat. © 2010 The Wildlife Society.     

Bees in the six: Determinants of bumblebee habitat quality in urban landscapes

With growing urbanization, it is becoming increasingly important to design cities in a manner that sustains and enhances biodiversity and ecosystem services. Native bees are critical pollinators that have experienced substantive declines over the past several decades. These declines have captured the attention of the public, particularly urbanites, prompting a large interest in protecting pollinators and their habitats in cities across North America and Europe. Unfortunately, we currently lack research about specific features of urban environments that can enhance the fitness of pollinators. We carried out an intensive study of Bombus impatiens, the Common Eastern Bumblebee, in the city of Toronto (Canada''s largest city), to better understand landscape parameters that provide high‐quality habitat for this species and likely other generalist bees. We divided the city into 270 grid cells and sampled a large number of worker bees, which were then genotyped at twelve hypervariable microsatellite loci. The genetic data allowed us to quantify the effective number of colonies and foraging distance for bumblebees in our study area. We then asked how the city''s landscape and human population demography and income are associated with the availability of high‐quality habitat for B. impatiens. Several aspects of Toronto''s landscape influenced colony density and foraging range. Urbanization had a clear effect on both colony density and foraging distance of workers. On the other hand, functional (i.e., not cosmetic) green space was often associated with higher quality habitats for bumblebees. Our study suggests several planning strategies to enhance habitat quality for bumblebees and other pollinators in cities.     

基于土地利用变化的福建省生境质量时空变化研究

地利用变化引起的生态效应已经成为生态学研究的核心问题,分析土地利用变化引起生境质量时空变化可以为生态保护和土地规划提供科学依据。以福建省为例,利用In VEST模型对福建省生境质量进行评估,根据生境质量指数将其生境划分为低、中、良好、优等。同时分析了福建省土地利用变化对其生境质量时空格局的影响。研究结果表明:2000—2010年,福建省景观破碎度指数逐渐降低,斑块之间连通性好,生境破碎化程度降低,整体生境得分值在0.9以上。林地是福建省的优势景观,其覆盖面积达到了福建省的86%以上,并且林地的破碎化程度低,人类活动对它的干扰较小,所以福建省大部分地区生境质量处于良好、优质等级。但是福建省东南沿海地区生境值低于0.6,处于中、低等级之间,主要因为建设用地的急剧扩张增加了对生境质量的破坏强度。东南沿海地区的GDP占到福建省的65%以上,形成了以二、三产业为主导的产业格局,对基础设施建设、工业、居住用地等的需求急剧增加。所以,福建省的57%以上的建设用地主要集中于东南沿海地区。东南沿海地区高度聚集的建设用地,侵占了大量的裸地和耕地,严重干扰了该地区整体生态格局,破坏了生境质量,导致其生境质量低于福建省其他地区。     

切尔诺贝利核事故对区域景观格局及生境质量的影响

灾难地景观格局及生境质量演化特征研究对于评估灾难破坏力及其滞后性,揭示人类活动对自然环境的影响机制具有重要意义。基于Landsat系列遥感影像提取切尔诺贝利隔离区景观类型结构,借助景观指数和InVEST模型刻画研究区近49年来的景观格局和生境质量演化轨迹,使用CA-Markov模型模拟核事故对区域生态景观的影响。研究表明：（1）切尔诺贝利核事故改变了隔离区原有的景观结构,导致耕地、建设用地等人为景观数量大幅缩减,土地利用程度显著下降,但核事故未对隔离区当前的景观结构造成实质性负面影响;（2）切尔诺贝利核事故致使隔离区人为干扰减少,植被连通性和集聚度提升,景观格局总体向好发展;（3）隔离区的设立扭转了区内生境质量恶化趋势,由耕地形成的低生境质量区域迅速转变为草地、林地等高生境质量区域,区内生境质量极大改善;（4）切尔诺贝利核事故使得区内高生境质量区域占比提升34%,改变了原有以耕地、建设用地不断扩张为主线的景观演化轨迹和生境质量不断退化的发展趋势。     

Effect of floating nest platforms on the breeding performance of Black Terns

ABSTRACT.   In 2003 and 2004, we placed 41 floating nest platforms on Grassy Lake in southeastern Wisconsin (USA) to test the hypothesis that reproductive success of Black Terns ( Chlidonias niger ) is limited by the quality of suitable nesting habitat. Extreme differences in water levels between these 2 yr provided a natural experiment to evaluate the effectiveness of the nest platforms during a drought year (2003) when natural nesting substrate was abundant, and a flood year (2004) when natural substrate was limited during the peak nesting period. Terns nested on 27 of 41 (66%) of the platforms in 2003 and 26 of 41 (63%) in 2004. No difference in the occupancy rate of platforms and natural nests was evident in 2003, but the pattern of clutch initiations early in the season in 2004 indicated that platforms were preferred over natural substrates. In 2003, nest survival rates did not differ between nests placed on platforms and those placed on natural substrates, but platform nests had significantly higher hatching success and nest survival rates in 2004. Both the Kaplan-Meier and Apparent Nest Success methods of calculating nest survival provided similar estimates. In both years, eggs laid on platforms were significantly larger than those laid on natural substrates, suggesting that platforms were occupied by high-quality birds. Our study indicates that floating nest platforms can be an effective management tool to enhance nesting habitat for Black Terns and other aquatic birds that construct floating nests, primarily because platforms provide nest sites when natural sites are not available due to flooding. Nest platforms also may be useful for addressing questions concerning habitat selection and parental quality.     

基于土地利用格局变化的北京市生境质量时空演变研究

城市生境质量对生物多样性保护有至关重要的作用,以北京市为例分析2000—2015年北京市不同土地利用类型的空间分布特征和不同区域之间的差异,并借助In VEST-Habitat Quality模型评估了北京市4个时期(2000年、2005年、2010年和2015年)、4个区域(首都功能核心区、城市发展新区、城市功能拓展区、生态涵养发展区)的生境退化程度和生境质量变化情况。结果表明:(1)从2000年到2015年,建设用地增加了近40%,耕地、湿地是其快速扩张的主要来源,城市发展新区的建设用地增加了60%;(2)主要的生态用地(林地、草地、湿地)所占比例总体增加了5.71%,但是总体景观结构异质性减弱,斑块破碎化程度加大;(3)生境质量总体下降了2%,表现出明显的区域差异,首都功能核心区和生态涵养发展区的生境质量总值逐渐升高;生境退化度逐渐增加,最严重的区域在城市功能拓展区以及平原-山区交界地带。对区域生态服务价值评估的有益探索,为今后进一步城市景观格局的构建和优化提供依据和参考。     

The effects of anthropogenic alteration of nesting habitat on rates of extra‐pair fertilization and intraspecific brood parasitism in Canada Geese Branta canadensis

Parentage studies have shown that alternative reproductive strategies are widespread in many avian taxa that were once thought to be monogamous. Recent anthropogenically mediated habitat change may have disrupted ecological factors, such as breeding density, which have given rise to inter‐ and intraspecific variation in the frequency of extra‐pair fertilization (EPF) and intraspecific brood parasitism (IBP). We used genetic analyses to quantify the incidence of alternative reproductive strategies exhibited within clutches of Canada Geese Branta canadensis maxima nesting in high‐ and low‐density situations in and around urban areas in southern Michigan, USA. We tested the hypothesis that high nesting density would increase the frequency of EPF and IBP. There were no significant differences in rates of EPF and IBP clutches (14 and 26% of clutches, respectively) from nests in high‐density (21.7% EPF, 21.7% IBP) vs. low‐density (5.3% EPF, 31.6% IBP) areas, although high‐density sites had a fourfold higher rate of EPF. Rates of EPF and IBP in high‐density urban areas in Michigan were comparable to rates observed in other species nesting under different ecological conditions. Levels of relatedness between host and parasitic females were higher than expected by chance, suggesting that related females are more tolerant of one another and that host females could gain inclusive fitness benefits from rearing parasitic offspring. Our study highlights the importance of understanding the different costs and benefits associated with alternative behavioural repertoires that may vary as habitats and associated selection pressures are increasingly modified by human activities.     

Changing land management of lowland wet grasslands of the UK: impacts on snipe abundance and habitat quality

Snipe Gallinago gallinago breeding on lowland wet grasslands in England have undergone widespread and dramatic declines in abundance and distribution since at least the 1970s. There are many potential drivers of the decline but reductions in habitat quality, driven by land management, are often proposed as a contributing factor in the historical declines of breeding waders. Breeding snipe are now restricted to a few key places such as nature reserves and environmentally sensitive areas where management for breeding waders is implemented. On average, populations have continued to decline, even in these key areas, though population trends vary from a decline of 98% to an increase of 61% between the early 1990s and 2006. We examined the relationship between regional variation in snipe population trends and soil conditions, other habitat features and land management. Snipe were more likely to persist in fields where the soil conditions were wet and soft. Fields are wetter and softer now than in the early 1990s and management influenced these conditions. Soil softness increased with decreasing grazing pressure and increasing surface flooding. Soil moisture increased with surface flooding and was higher in organic soils. Changes in field condition were consistent with decreases in grazing pressure and increases in surface flooding. In spite of habitat condition being altered in a way that should have been beneficial to snipe, the numbers have continued to decline. Thus, it is unlikely that the measures of habitat condition examined here have been the driver of the decline and other factors must be involved. Research efforts should now focus on alternative explanations of the decline, for example, changes in other key aspects of habitat quality such as prey abundance, or changes in snipe productivity or mortality.     

城市扩张导致京津冀区域生境质量下降

城镇化发展极大地改变了区域生境分布格局和功能,从而影响区域生态安全。因此,开展生境质量的评估,对于城市生态安全保障具有重要作用。基于In VEST生境质量模型,评估了京津冀区域2005—2015年生境质量时空变化格局。研究结论如下:1)2005—2015年,京津冀生境面积减少7134.2 km~2,占2005年生境面积的3.7%。耕地、草地和水域生境面积分别减少5081.0、1695.1、421.6 km~2,占对应类型生境面积的4.7%,4.9%和7.2%。2)京津冀生境质量从0.88降至0.83,下降幅度达5.69%。其中,耕地生境质量下降最为严重,其次为水域生境质量。3)生境质量下降区域主要沿北京-保定-石家庄-邢台-邯郸等经济发展迅速的区域分布,表现为城市扩张侵占原有生境。4)京津冀高生境质量斑块破碎度增加,低生境质量斑块集聚度增加。整体上看,京津冀区域生境斑块破碎度增加。     

生境破碎化过程对流域生境质量的影响

近几十年来,随着工业化、城市化的加速推进,人类活动对自然生境的干扰越来越频繁,导致生境破碎化与生境质量下降。在流域尺度上科学模拟生境破碎化过程及其对生境质量的影响,对于提升生物多样性和生态系统功能具有重要意义。以鄱阳湖流域为研究区域,基于InVEST模型分析区域生境质量的演变特征;从生境面积、生境边缘和生境隔离三个特征维度模拟生境破碎化过程;采用广义加性模型和地理探测器探究不同生境破碎化过程对生境质量变化的影响与交互作用。研究结果表明:(1)鄱阳湖流域生境质量呈下降趋势,从2000年的0.7862下降到2010年的0.7807,再下降到2020年的0.7715,但总体生境质量较好。生境质量较优的区域主要分布在流域南部、东北部以及西部地区,生境质量较差的区域主要分布在各个子流域的交界处。(2)2000-2010年,鄱阳湖流域生境面积占比下降、生境边缘增加和生境隔离增加三个生境破碎化过程分别占总研究区网格数的34.70%、30.15%和4.50%;2010-2020年分别占总研究区网格数的34.80%、30.69%和4.40%;2000-2020年分别占总研究区网格数的40.82%、37.50%和5.46%。生境面积减少的网格主要集中在鄱阳湖流域的中北部地区;生境边缘增加的网格分布和生境面积减少的网格分布相似;相比之下,生境隔离增加的网格较少,主要分布在各城市的中心城区范围。(3)生境破碎化过程对生境质量具有显著影响,两者呈非线性负相关关系;三个生境破碎化过程两两之间交互作用对生境质量的影响呈现双因子增强趋势。研究结果可为鄱阳湖流域生态格局优化与生境质量提升提供科学参考。