Do Newly Built Urban Parks Support Higher Bird Diversity? Evidence from the High-Density Urban Built-Up Area of Zhengzhou, China

Abstract

Rapid urbanization has resulted in widespread habitat loss and fragmentation, threatening global biodiversity. Urban parks serve as essential refuges for wildlife within cities, particularly for birds, which are sensitive indicators of ecosystem health and habitat quality. In recent years, numerous Chinese cities have begun integrating biodiversity-friendly design approaches into new park development. However, the effectiveness of these strategies remains insufficiently evaluated. This study assesses the ecological performance of newly built parks by examining 11 recently constructed parks (within the past decade) and 9 historical parks in Zhengzhou, China’s high-density urban area. Monthly bird surveys were conducted across all 20 parks from May to December 2020, covering breeding, post-breeding, and overwintering seasons. Our findings reveal that new parks significantly outperformed old parks in bird abundance, species richness, Shannon diversity index, and functional diversity. Analysis of environmental variables at both local (within-park) and landscape (1-km buffer) scales showed that habitat diversity and multi-layered vegetation structure were the most influential local factors promoting bird diversity, while green space connectivity was the primary landscape-scale contributor. Notably, neither park area nor age significantly predicted diversity patterns. Based on these results, we propose three key planning strategies: (1) enhancing habitat diversity within parks to support species from various ecological niches; (2) implementing multi-layered vegetation planting to provide diverse food resources and nesting opportunities; (3) improving green space connectivity to facilitate species movement and population persistence within urban environments. These findings provide valuable insights for designing more effective biodiversity-friendly urban green spaces.

1. Introduction

Rapid urbanization represents one of the most significant forms of land-use change, profoundly transforming landscapes and ecosystems across the globe [1]. The expansion of urban infrastructure frequently encroaches upon natural and semi-natural habitats, resulting in extensive habitat loss, degradation, and fragmentation [2]. As a consequence, urbanization has emerged as a major driver of global biodiversity loss, altering species composition, disrupting ecological processes, and imperiling numerous native species [3,4]. With trillions of dollars projected for global infrastructure development in the coming decades, these pressures are expected to intensify, underscoring the critical need to reconcile urban growth with biodiversity conservation [5,6].

Amid these challenges, urban green spaces (UGS)—such as parks, gardens, cemeteries, and remnant natural areas—have gained recognition as vital components of urban ecosystems [7]. These green patches serve as key refuges, providing foraging and breeding grounds for diverse flora and fauna, and act as biodiversity hotspots within largely built-up environments. Among UGS, urban parks are often the most extensive and structurally complex, playing an especially important role in sustaining urban biodiversity [8] and delivering essential ecosystem services to residents [9]. Beyond functioning as isolated habitats, parks are increasingly viewed as potential nodes within broader ecological networks that support species movement and persistence in urban settings [10]. Thus, identifying how to design and manage urban parks to enhance their ecological functionality is a fundamental to sustainable urban planning.

Birds are widely regarded as ideal indicator taxa for assessing the ecological quality of urban green spaces and monitoring the impacts of urbanization [11]. They are highly responsive to environmental changes, with shifts in community structure, species richness, and abundance reflecting variations in habitat complexity, resource availability, and anthropogenic pressure [12]. Moreover, birds perform numerous ecological functions—including pollination, seed dispersal, pest control, and scavenging—that contribute to ecosystem health and stability [13], Their relative ease of observation and public appeal also make birds effective focal species for citizen science initiatives, promoting public engagement and environmental awareness [14,15,16,17].

Decades of ecological research have established consistent patterns in avian responses to urbanization [18]. Typically, bird community composition shifts markedly along rural-to-urban gradients [19]. Specialist and sensitive species often decline or are extirpated [20], while generalist, adaptable, and often non-native species tend to dominate [21]. Although highly urbanized areas usually exhibit reduced overall species richness [22], some studies note a peak in diversity at intermediate levels of disturbance—a pattern consistent with the intermediate disturbance hypothesis in urban ecological systems [23].

The structure and composition of urban bird communities are shaped by factors operating across multiple spatial scales, ranging from microhabitat features within parks to the broader urban landscape context. Understanding these multi-scale drivers and their interactions is essential for effective urban biodiversity conservation [22]. At the local (or patch) scale, park attributes play a decisive role [24]. Park area often serves as a strong positive predictor of species richness, aligning with the principles of island biogeography [25]. However, habitat quality and structural complexity are frequently more influential than size alone [26]. Parks with high plant species diversity—particularly native vegetation—and multi-layered vegetation structure (incorporating ground cover, shrubs, and canopy trees) provide a broader array of ecological niches, food resources (such as insects, seeds, and nectar), and nesting sites, thereby supporting richer avian assemblages [27,28,29]. Tall, mature trees act as keystone structures that significantly enhance bird diversity. The presence of water bodies and a reduction in intensively managed areas (e.g., highly manicured lawns) in favor of more natural habitats features also positively affect bird diversity [30]. Conversely, habitat simplification practice, such as replacing natural grass with artificial turf, can adversely affect bird communities [31].

At the landscape scale, the spatial context of a park is equally critical. Urban parks do not function as isolated ecological islands; the migration, dispersal, and long-term survival of their species depend strongly on connectivity with surrounding habitats [22]. High percentages of impervious surface cover in the adjacent matrix tend to reduce diversity [32], whereas proximity to larger natural patches or riparian corridors can serve as species sources, enriching local species richness [10,33]. Parks embedded within well-connected green infrastructure networks—such as those linked by tree-lined streets or smaller green patches—are more likely to sustain metapopulations and maintain higher long-term ecological integrity [34,35].

Despite these insights, important gaps persist, especially concerning the practical implementation of ecological principles in urban planning and the evaluation of their outcomes [36]. Although biodiversity-friendly design is increasingly integrated into urban development projects [37,38,39], most ecological studies have focused on established, historic parks or compared different types of urban park systems (UGS) (e.g., parks, golf courses, residential courtyards). There remains a scarcity of empirical studies directly evaluating the ecological performance of newly constructed parks through systematic comparison with traditionally designed parks within the same urban system [40,41]. A critical unanswered question is whether these newer parks, designed with explicit ecological intentions, actually support higher levels of biodiversity. Addressing this question is essential for validating current design approaches and offering evidence-based guidance for future urban greening, particularly in high-density, rapidly urbanizing cities in China [42,43,44].

This study aims to fill these research gaps by conducting a comparative analysis of bird diversity in new versus old urban parks in Zhengzhou, a densely populated megacity in central China experiencing rapid urbanization. We systematically assessed the effectiveness of contemporary park design in supporting avian diversity by examining not only taxonomic metrics (species richness and abundance) but also functional diversity, which reflects the variety of ecological roles played by species within a community and serves as a key indicator of ecosystem health and resilience [45,46]. In addition, we identified multi-scale environmental drivers—both local and landscape-level—underlying observed variations in bird diversity.

Specifically, we tested the following hypotheses:

• Newly built parks (constructed within the last decade) having incorporated modern ecological design principles support significantly higher bird abundance, species richness, and functional diversity compared to older, traditionally designed parks.
• At the local scale, greater habitat diversity and a higher proportion of multi-layered vegetation structure are the primary factors driving enhanced bird diversity in newer parks.
• At the landscape scale, higher connectivity to surrounding green infrastructure positively affects bird diversity across all parks, with particularly strong benefits for species dispersal in newer parks.

By testing these hypotheses, our study provides empirical evidence on the ecological outcome of different park development models. The findings offer practical insights for urban planners, landscape architects, and policymakers to support the design of more biodiverse and resilient urban green spaces.

2. Materials and Methods

2.1. Study Area and Park Selection

This study was conducted in Zhengzhou (112°42′–114°14′, 34°16′–34°58′), the capital of Henan Province, China (Figure 1). Zhengzhou has a temperate continental monsoon climate. It is a major transportation hub in China and a prime example of a rapidly urbanizing, high-density city. Over the past two decades, Zhengzhou’s urban area has expanded dramatically, with a permanent population exceeding 12 million. As part of its urban development plan, the Zhengzhou municipal government has maintained several historic parks while also constructing numerous new ones, providing an ideal setting for comparative research. In 2011, Zhengzhou decided to develop itself into a “National Forest City” and formulated the “Zhengzhou Forest City Construction Master Plan (2011–2020).” Subsequently, Zhengzhou has built a series of new urban parks in accordance with this plan, increasing the area of urban green space and adjusting its landscape pattern to maximize its ecosystem services. Most of these new parks are required to incorporate ecological and biodiversity-friendly strategies in their planning and design.

We selected 20 public urban parks in the high-density built up areas of Zhengzhou as research sites which are relatively evenly distributed in space (Figure 1). Based on the age of the parks, we divided them into two groups: the “new parks” group (n = 11), defined as parks built and open to the public less than 10 years ago (built between 2011 and 2020); and the “old parks” group (n = 9), defined as parks built over 20 years ago (built before 2000), representing more traditional park designs (

Table 1. The district to which the selected park belongs, its area, transect length, and year of construction.

Number	Park Name	District	Area (ha)	Built Year	Line Length (km)	Group
1	Lianhua Park	Huiji	10.73	2011	1.3	New
2	Longhu Wetland Park	Jinshui	19.38	2017	2.3	New
3	National Forest Park	Jinshui	165.83	2018	6.8	New
4	Wenhua Park	Jinshui	8.03	1999	1.2	Old
5	Sculpture Park	Zhongyuan	37.43	2015	2.5	New
6	Xiliuhu Park	Zhongyuan	112.01	2012	5.1	New
7	Bishagang Park	Zhongyuan	26.84	1957	2.3	Old
8	Renmin Park	Erqi	31.4	1952	2.7	Old
9	Zijingshan Park	Jinshui	19.18	1960	1.9	Old
10	Zhengzhouzhilin	Jinshui	28.87	2006	3.4	Old
11	Hongbaihua Park	Jinshui	13.25	2008	1.6	Old
12	Lonzihu Park	Jinshui	65.03	2016	3.8	New
13	Botanic Garden	Zhongyuan	57.4	2009	3.9	Old
14	Jialu River Park	Zhongyuan	75.31	2016	3.6	New
15	Shuangxiu Park	Erqi	4.25	1987	0.8	Old
16	Binhe Park	Guancheng	39.82	2014	1.8	New
17	Zhengzhou Arboretum	Erqi	279.72	2015	8	New
18	Diehu Park	Guancheng	68.34	2020	4.7	New
19	Lvgu Park	Huiji	28.31	2014	2.1	New
20	Jingxiu Park	Erqi	9.08	1980	1.1	Old

). When selecting the sites, we attempted to ensure that the two groups were comparable in terms of area distribution to minimize the potential influence of park area as a confounding variable. The selected parks ranged in size from 4.25 ha to 279.72 ha, encompassing the typical sizes of small and large urban parks, with some differences in infrastructure and vegetation characteristics.

2.2. Bird Census in Urban Parks

We conducted avian surveys in each of the 20 parks on eight occasions between May to December 2020. This survey period was designed to cover the breeding, post-breeding, and wintering seasons—based on historical bird records of the region—thus capturing the majority of bird species inhabiting Zhengzhou (except for the precociously migrating birds in March–April). Bird communities were surveyed using the line transect method [47]. One fixed transect route was established, with its total length scaled proportionally to the park area. Surveys were carried out by experienced observers between 06:00 and 10:00 h on days without strong winds or heavy rain. Observers walked at a steady pace of approximately 1.5 km/h and recorded all birds seen or heard within 50 m of the transect line. Species were identified and counted; however, birds merely flying over the park without using any habitat within it were excluded from the records.

During the survey, we also recorded the habitat type in which the birds appeared and divided the habitat types into the following 10 types: (1) deciduous forest; (2) coniferous forest; (3) mixed coniferous and deciduous forest; (4) dense shrubs; (5) sparse shrubs; (6) grassland; (7) water surface; (8) water edge; (9) open space; (10) buildings.

2.3. Bird Diversity Metrics

For each park, we calculated four diversity metrics based on the cumulative data from all eight surveys:

Abundance: The total number of individual birds recorded.

Species Richness: The total number of bird species recorded.

Avian diversity Index was calculated based on the Shannon–Wiener Index (H′), which is as follows:

$$\mathrm{H}\prime =-\sum {\mathrm{p}}_{\mathrm{i}}\ln \left({\mathrm{p}}_{\mathrm{i}}\right)$$

where pi is the proportion of individuals belonging to the i-th species. This index accounts for both species richness and evenness.

Functional Diversity (FD): We used the functional dispersion index (FDis) [48] for calculation. We compiled a trait database for all recorded species, including resource use, migration, feeding, and habitat preferences, categorizing them into three categories: diet, residence type, and habitat type, which is as follows:

$$\mathrm{F}\mathrm{D}\mathrm{i}\mathrm{s}={\displaystyle \frac{\sum {\mathrm{a}}_{\mathrm{j}}{\mathrm{z}}_{\mathrm{j}}}{\sum {\mathrm{a}}_{\mathrm{j}}}}$$

where aj denotes the abundance of species j, and zj represents the distance from species j to the weighted centroid c. The formula for calculating the weighted centroid c is:

$$\mathrm{c}={\displaystyle \frac{{\sum }_{\mathrm{j}}{\mathrm{a}}_{\mathrm{j}}{\mathrm{x}}_{\mathrm{j}}}{{\sum }_{\mathrm{j}}{\mathrm{a}}_{\mathrm{j}}}}$$

where xj is the coordinate vector of species j in functional trait space.

2.4. Environmental Variables

We considered environmental variables at two scales: local and landscape. Local-scale variables include park area, water body area, habitat diversity, and multi-layered planting area in each urban park. At the landscape scale, using a 1 km buffer zone around urban parks (Figure 2), we obtained indicators such as green space connectivity, impervious surface proportion, green space area proportion, average building height, population density, and POI density. The environmental variables and data sources are shown in the table (

Table 2. Definition and data source of environment variables.

Scale	Variations	Definition	Data Source
Local-scale	Park area	Total area of the park	ArcGIS10.2--2020.5-8 Aerial raster data from drones
	Multi-layered planting area	vegetated area with a clear vertical structure comprising trees, shrubs, and herbaceous ground cover
	Water body area	water body cover in parks
	habitat diversity	bird survey habitat variety	field survey
Landscape-scale	Green space connectivity	1 km-buffer green space connectivity	ArcGIS 10.2-(GF-2) 2020 https://www.resdc.cn/(accessed on 15 May 2020)
	impervious surface proportion	1 km-buffer impervious surface proportion
	Green space area	1 km-buffer green area
	average building height	1 km-buffer average building height	open street map https://master.apis.dev.openstreetmap.org/(accessed on 20 December 2020)
	population density	1 km-buffer average population density	Worldpop100 m https://worldpop.Ldpop.org/(accessed on 20 December 2020)
	POI density	1 km-buffer POI density	https://lbs.amap.com/(accessed on 20 December 2020)

).

Park area and water body area: Calculated from high-resolution satellite imagery in ArcGIS 10.2.

Multi-layered planting area: This was defined as the vegetated area with a clear vertical structure comprising trees, shrubs, and herbaceous ground cover. This was assessed through detailed field surveys and analysis of UAV imagery.

Green Space Connectivity: The index was calculated using Conefor Sensinode 2.6 (Figure 3).

2.5. Statistical Analysis

All statistical analyses were performed in R version 4.1.2.

First, we used one-way analysis of variance (ANOVA) to test for significant differences in the four bird diversity metrics (Abundance, Species Richness, Shannon Diversity, and Functional diversity) between the new and old park categories.

Next, to identify the key drivers of bird diversity, we used multiple linear regression. Prior to analysis, we tested for multicollinearity among predictor variables using Pearson correlation coefficients; variables with |r| > 0.7 were considered collinear and were not included in the same model. We then evaluated all possible model combinations using the corrected Akaike Information Criterion (AICc) to rank these models. Model support was assessed using ΔAICc (the difference in AICc between each model and the best-supported model). Models with ΔAICc < 2 were considered to have strong support. Akaike weights (w_i) were calculated for each model based on ΔAICc, representing the relative probability that a given model is the best among the candidate set. The model with the highest w_i was selected as the most parsimonious. Finally, we calculated the summed Akaike weight for each environmental variable across all models in which it appeared, to assess its relative importance in explaining bird diversity.

3. Results

3.1. Overall Bird Community

Across the 20 parks and eight survey periods, we recorded a total of 19574 individual birds belonging to 159 species (Supplementary Table S1) in 40 families (Figure 3). The most abundant species were the Passer montanus (48.64%), Cyanopica cyanus, Pica pica, Spilopelia chinensis, and Turdus mandarinus, which are common urban-adapted species. The top ten species accounted for 81.87% of the total number of bird surveys. However, we also recorded several species of conservation interest, including Emberiza aureola and Aythya baeri, which are Critically Endangered species, primarily in the larger, more habitat-diverse new parks.

With the acceleration of urbanization, some bird species have become increasingly adapted to the urban environment, especially insectivorous birds and omnivorous birds, which have become the dominant groups.

Based on the literature review and observations during the survey on the resource utilization, migration, feeding and habitat preferences of birds, the following groups were formed (

Table 3. Functional trait groupings for all recorded bird species.

Group		Count
Resident Type	Resident	47
	Passage Migrant	42
	Summer Visitor	52
	Winter Visitor	14
	Accidental	4
Feeding Habits	Granivores	14
	Predatory	11
	Insectivorous	65
	Omnivorous	69
Habitat Type	Forest	84
	Water	42
	Near Water	17
	Other	16

):

Passage Migrant: species for which the area is not part of its breeding or wintering grounds but is consistently used as a stopover during seasonal migration.

Accidental: species observed in an area far beyond its known, established geographic distribution or migration routes, with occurrences being infrequent and unpredictable.

Bird abundance and species richness showed significant differences among the 20 parks (Figure 4) (Supplementary Tables S2 and S3). Longhu Wetland Park had the highest average abundance (160.75) and species richness (31.375), while Wenhua Park and Shuangxiu Park had the lowest average abundance (83.5, 85.5) and species richness (14.25, 14).

The average Shannon–Wiener Diversity Index for the 20 urban parks was 2.59 (Supplementary Table S4). Longhu Wetland Park and Jialu River Park had average diversity indices exceeding 3, at 3.04 and 3.2, respectively. Parks with lower Shannon–Wiener indices were People’s Park, Hongbaihua Park, Cultural Park, Shuangxiu Park, and Jingxiu Park, at 2.27, 2.35, 2.15, 2.37, and 2.36, respectively.

The average functional dispersion index for the 20 urban parks was 0.38 (Supplementary Table S5). Longhu Wetland Park and Xiliuhu Park had higher functional dispersion indices, at 0.49 and 0.48, respectively. This indicates that these parks have a greater variety of habitat types or abundant food sources, allowing them to accommodate a wider range of bird species with different feeding habits and habitat preferences. Green spaces with lower functional dispersion indices were Shuangxiu Park and Hongbaihua Park, at 0.26 and 0.28, respectively.

Among parks with high bird diversity indices, Longhu Wetland Park (Figure 5A,B), completed in 2017, is one of the few artificial wetlands in Zhengzhou that protects and restores natural aquatic ecosystems. Its construction effectively integrates and connects surrounding water systems and green space resources. Composed of multiple ecological islands of varying sizes, the park utilizes a rich plant community to create a near-natural wetland environment, boasting a high bird diversity and becoming a popular spot for birdwatching and photography.

The Jialu River Park (Figure 5C,D), built in 2016, is connected to the Jiangang Reservoir in Zhengzhou Water Source Protection Area upstream, and crosses the South-to-North Water Diversion Canal downstream to connect to Xiliu Lake. It is adjacent to the Changzhuang Reservoir to the west. It has abundant water and a natural river valley landscape. It has a good natural ecological background, and pays attention to preserving the original style and curvature of the river channel in the water body design, creating an ecological environment that protects the original ecology and is inhabited by a variety of organisms.

Xiliuhu Park (Figure 5E,F), originally constructed in 2011, underwent an ecological renovation in 2018. Leveraging the site’s topography and incorporating sponge city theory, the park created an ecological green belt that collects rainwater, directs runoff, and filters water. Building on the existing terrain, the park also created a self-repairing, water-filtering artificial wetland, which collects rainwater and directs runoff back into the river. The natural ecological environment supports a high bird population and diversity.

Traditional parks, such as Wenhua Park (Figure 5G) and Shuangxiu Park (Figure 5H), have lower bird diversity. These parks were primarily designed for human viewing and recreation, resulting in a monotonous vegetation composition and structure, and frequently mowed lawns, which limited bird food and habitat resources. Furthermore, because these parks are located in close proximity to residential areas, they often feature a high proportion of hard paving to cater to the recreational needs of surrounding residents (such as senior citizens’ square dancing and choir rehearsals).

3.2. Comparison of Bird Diversity Between New and Old Parks

The results of the one-way ANOVA revealed significant differences between new and old parks for all four bird diversity metrics (Figure 6). Newly parks consistently supported higher levels of bird diversity. Specifically, new parks had significantly greater total abundance (p = 0.0209), higher species richness (p = 0.0007), a higher Shannon diversity index (p = 0.0036), and greater functional richness (p = 0.0019) compared to old parks. These findings indicate that, on average, the newly established parks support higher avian abundances and a greater diversity of bird species. Moreover, bird populations within these parks demonstrate a more balanced distribution, contributing to a more stable community structure. The coexisting species also occupy a broader range of functional traits—such as those related to diet and foraging behavior—suggesting that avian assemblages in new parks utilize a wider spectrum of ecological niches.

3.3. Drivers of Bird Diversity

After testing for collinearity, eight environmental variables were retained for model selection (impervious surface was selected from the landscape-scale proportion of green space and proportion of impervious surface). Model selection results consistently emphasized the importance of local habitat characteristics and landscape connectivity in shaping bird communities (Figure 7;

Table 4. Diversity indicators and predictor variable model selection results based on the AICc.

Indicator	Model	AICc	Δ AICc	wi	adjR2
Abundance	Habitat diversity + Impervious surface ratio + Water Body Area	166.35	0	0.133	0.744
Species Richness	Habitat Diversity + Connectivity	143.96	0	0.128	0.676
Shannon DI	Connectivity + Multi-layered Planting Area	−9.67	0	0.173	0.443
Functional DI	Multi-layered Planting Area + Impervious surface ratio + Habitat Diversity	−33.57	0	0.122	0.566

).

For Abundance, the habitat diversity (w+ = 0.73, p < 0.01), Impervious surface ratio (w+ = 0.61, p < 0.05) and Water Body Area (w+ = 0.57, p < 0.05) were the significant predictors. This is basically consistent with the results of previous studies, indicating that the richer the habitat types within the park, the larger the water area, and the lower the intensity of surrounding urbanization, the more birds are observed in the park.

For Species Richness, the best-fit model included Habitat Diversity (w+ = 0.93, p < 0.01) and Green Space Connectivity (w+ = 0.71, p < 0.05). This suggests that the number of bird species a park can accommodate depends not only on the habitat complexity within it, but also greatly on the landscape context of the area in which it is located: parks that are better connected to surrounding green spaces and surrounded by low-urbanization environments have higher species counts.

For the Shannon–Wiener Diversity Index, the Multi-layered Planting Area (w+ = 0.89, p < 0.01) and Green Space Connectivity (w+ = 0.87, p < 0.01) were the strongest predictors, and they are all significantly positively correlated with the Shannon–Wiener index of birds. This result indicates that parks with complex vertical vegetation structures and located in highly connected landscapes have bird communities composed of more species and a more balanced distribution of species.

For Functional Richness, Multi-layered Planting Area (w+ = 0.86, p < 0.01), Impervious surface ratio (w+ = 0.65, p < 0.05) and Habitat Diversity (w+ = 0.60, p < 0.05) were the significant predictors. This means that the more complex vegetation structure and more diverse habitat types within the park provide the required exclusive ecological niches for birds with different functional characteristics (such as obligate insectivorous birds), but this effect will be weakened by the high-intensity urbanization in the surrounding area.

Across all models, two variables—Park Area and Population Density—were consistently absent from the top-ranked models and showed no significant effects on any of the bird diversity metrics.

4. Discussion

Against the backdrop of accelerating global urbanization, mitigating its negative impacts on biodiversity has become a central challenge for sustainable development. Using the rapidly urbanizing Chinese city of Zhengzhou as a case study, this study offers robust empirical evidence for the effectiveness of proactive ecological planning. By comparing avian communities between newer, ecologically designed parks incorporating biodiversity-friendly principles and older, traditional ones, we demonstrate that purposefully designed green spaces markedly enhance bird diversity. Our core findings strongly support our primary hypothesis (H1): newer parks with deliberate ecological design significantly outperformed older parks across four key metrics—avian abundance, species richness, the Shannon–Wiener Index, and functional dispersion. These results underscore that the ecological value of urban green spaces is not merely a function of their existence, but rather depends critically on the quality of their internal habitat structure and their strategic integration into the broader urban landscape.

4.1. The Efficacy of Biodiversity-Friendly Design: Why New Parks Perform Better

Our findings demonstrate that the “ecological philosophy and biodiversity-friendly design” promoted in newer parks is not merely rhetorical but has been effectively translated into practice, yielding tangible ecological benefits. In contrast to some European studies where older parks exhibit higher biodiversity due to prolonged natural succession [49], our results clearly indicate that in Zhengzhou, habitat quality far outweighs park age as a determinant of ecological value. This discrepancy may be attributed to the fact that older parks in European contexts often undergo ecological maturation, developing stable ecosystems with greater resource abundance (e.g., seeds and insects). In contrast, many older parks in Zhengzhou were designed primarily for ornamental and recreational purposes, characterized by simplified plant community structures—often lacking shrub layers and diverse ground cover—and dominated by monotypic habitats such as expansive lawns and paved plazas. These areas are also subject to more intensive human disturbance and maintenance regimes, including frequent mowing and pesticide application, which further diminish their ecological functionality.

In comparison, newer parks appear to have been intentionally designed with ecological principles integrated from the outset. Strategies such as creating vegetation mosaics and diverse habitat patches, preserving or constructing water bodies, and introducing native plant species [16,50] have enabled these spaces to rapidly provide complex structures and niche variety. This approach of “designed ecology” facilitates the swift establishment of rich avian communities, underscoring how ecologically informed planning can accelerate the development of functional urban green spaces. Such interventions allow these ecosystems to deliver biodiversity conservation benefits promptly, without awaiting decades of natural succession—a critical advantage in rapidly urbanizing regions [51]. Our analysis directly corroborates the importance of these habitat features, showing that habitat diversity and multi-layered vegetation coverage are key drivers of enhanced biodiversity metrics. Thus, the superior performance of new parks is not coincidental but a direct outcome of their ecologically oriented design philosophy.

4.2. Interpreting the Multi-Scale Drivers of Avian Diversity

Our models indicate that different avian diversity metrics are influenced by distinct environmental factors, suggesting that bird communities respond to urban environments through multiple ecological perspectives.

The Central Role of Habitat Heterogeneity: Habitat diversity emerged as the strongest positive predictor of both species richness and abundance, aligning with existing literature [52]. Environments comprising mosaics of woodlands, shrublands, grasslands, and water bodies provide varied foraging, nesting, and shelter opportunities for species with differing ecological requirements, thereby facilitating greater species coexistence [53]. Notably, along with multi-layered vegetation coverage, habitat diversity also serves as a key driver of the Functional Dispersion Index (FDis). This implies that beyond merely increasing species richness, habitat complexity and heterogeneity are crucial for promoting functional diversity and supporting specialized species such as certain insectivorous birds. These findings help explain why the avian communities in newer parks are enhanced not only in numerical abundance but also in functional composition [54,55].

The Importance of Vegetation Structure: The extent of multi-layered vegetation exhibited a particularly strong positive association with both the Shannon–Wiener Index and FDis. Complex vertical structures—integrating tree, shrub, and herb layers—foster a wider variety of microhabitats and ecological niches [56,57]. For instance, species such as Lanius schach prefer perching on high branches with broad views for foraging, whereas Pycnonotus sinensis frequents the mid-canopy. In contrast, Phoenicurus auroreus and Tarsiger cyanurus are commonly found in lower trees and tall shrubs, Sinosuthora webbiana often remains concealed within dense shrubbery, and Turdus mandarinus and Upupa epops typically forage and rest on lawns. Multi-layered vegetation also offers safer nesting sites and improved protection from both predators and human disturbance [58]. For example, our surveys documented that Oriolus chinensis and Terpsiphone incei nested exclusively in poplar trees near water bodies in areas with minimal human activity. Such structural diversity promotes resource partitioning [59], reduces interspecific competition [60], and ultimately contributes to bird communities characterized by more even species abundance (higher Shannon index) and greater functional diversity [61,62].

The Attraction of Water Bodies: The presence of water areas significantly positively influenced bird abundance [63,64]. As natural water sources are often limited in urban settings, ponds, streams, or lakes within parks serve not only as essential habitats for waterbirds [65,66] but also as critical resources for drinking and bathing for all avian species. Consequently, water bodies act as significant attractors, markedly enhancing local bird abundance.

The Constraining Effect of Landscape Context: Our results underscore that the ecological benefits of well-designed parks can be substantially diminished by unfavorable surrounding landscape conditions [10]. The proportion of impervious surface within a 1-km buffer zone exerted strong negative effects on abundance and functional diversity [32]. High-intensity urbanization introduces noise, light pollution, human disturbance, increased risk of traffic collisions, and higher densities of predators, which together create an “ecological trap” or barrier that inhibits birds from utilizing—or even accessing—green spaces isolated within urban matrices.

Conversely, the positive influence of green space connectivity on species richness and the Shannon–Wiener Index highlights that parks embedded within well-connected green infrastructure networks can benefit from ongoing species dispersal and genetic exchange with surrounding populations. This connectivity is vital for sustaining long-term community stability and diversity. The contrasting roles of these landscape factors—connectivity versus imperviousness—reinforce the fundamental concept that urban parks cannot be considered in isolation from their broader environmental context.

4.3. Rethinking the Importance of Park Area and Population Density

Contrary to the well-established species–area relationship emphasized in ecological literature [10,11], our study found that park area was not a significant predictor of bird diversity in Zhengzhou [67]. This discrepancy may reflect a distinctive aspect of urban ecological systems: in densely built-up environments such as Zhengzhou, habitat quality and heterogeneity appear to be more important than size alone. A small park with high habitat diversity and complex vegetation structure can support richer bird communities than a large but homogenous park dominated by simplified landscapes such as lawns. This observation aligns with recent studies suggesting that clusters of small parks can collectively sustain high species richness through beta diversity [68]. This is an encouraging insight for urban planners, as it implies that significant ecological gains can be achieved even within space-constrained urban centers.

For example, Longhu Wetland Park, with an area of only 19 ha, exhibited the highest average bird diversity among the studied parks. In contrast, larger parks such as Bishagang Park and Binhe Park supported relatively low bird diversity. These parks contain extensive paved squares (Figure 8A), channelized river segments (Figure 8B), and recreational infrastructure such as fountain plazas and running tracks—features that provide limited habitat value for birds.

Furthermore, connectivity at the landscape scale may compensate for the limited area of individual parks by facilitating movement among green patches, thereby mitigating the constraints imposed by size [69]. The strong positive effect of green space connectivity on species richness and the Shannon–Wiener index underscores that urban parks are not isolated entities. A small but well-connected park can act as a stepping stone for dispersal, allowing for continuous immigration from larger source populations and thus helping maintain high species diversity. Therefore, our findings do not refute island biogeography theory but rather extend it from a focus on “island area” to the concept of an “island network” [70]. The collective ecological value of a well-connected system of small parks may exceed that of a single large isolated park.

Similarly, the lack of a significant effect of surrounding human population density was unexpected. This may suggest that in a highly urbanized setting like Zhengzhou, bird communities have become habituated to consistent human presence. Alternatively, high-quality park design—such as incorporating dense thickets or undisturbed islands within water bodies—may effectively buffer human disturbances, providing refuge areas that reduce the impacts of anthropogenic activity.

4.4. Management Implications and Planning Recommendations

Our findings offer evidence-based guidance for urban planners, landscape architects, and park managers to enhance urban biodiversity through the following recommendations:

Prioritize Habitat Heterogeneity and structural complexity: In both the design of new parks and the renovation of existing ones, emphasis should be placed on actively creating diverse habitat patches—such as woodland areas, shrub zones, wildflower meadows, and ecological swales—rather than adhering to the conventional “lawn with scattered trees” model [71]. The establishment of multi-layered native plant communities should be mandated in design standards to ensure complete vertical stratification and provide full ecological niches for wildlife [72].

Incorporate water features as core biodiversity elements: Even in space-constrained parks, the inclusion of small-scale water elements such as shallow ecological ponds or rain gardens is recommended. These features not only promote avian diversity [73] but also deliver additional ecosystem services including stormwater management, microclimate cooling, and humidity regulation.

Adopt systematic landscape-scale planning: Site selection for new parks should prioritize proximity to existing green corridors or key nodes within urban ecological networks to enhance connectivity [16,74,75]. For established parks, urban policies should encourage the creation of ecological buffer zones that limit high-intensity development and promote low-density, green-oriented land uses—such as community gardens and greenways—to mitigate the negative effects of adjacent impervious surfaces. Furthermore, future planning should aim to link isolated parks through integrated ecological corridors, such as riparian vegetation zones and tree-lined pathways, to establish a functional and resilient urban ecological network.

4.5. Limitations and Future Directions

This study offers a robust within-city comparison; however, its conclusions should be validated across urban settings with varying climatic conditions, spatial structures, and regional species pools [76]. Furthermore, while our eight-month survey detected breeding, post-breeding, and overwintering phases, it did not cover the very early spring migration period (March–April). Consequently, our study did not record ‘precociously migrating’ bird species that pass through the urban area during this window. Future research incorporating year-round and long-term monitoring would provide a more complete picture of avian community dynamics in urban parks, and help clarify how avian communities respond to successional changes in vegetation.

Future research should also examine the effects of specific management practices—such as pesticide application, mowing frequency, and levels of public access—on bird assemblages. Controlled experimental approaches, including the deliberate addition or removal of habitat features, could strengthen causal inference regarding the mechanisms underlying urban park biodiversity [77]. Moreover, expanding studies to include other key taxonomic groups, such as insects and mammals, is essential for a more comprehensive understanding of urban ecosystem functioning [78].

Finally, integrating environmental justice principles is critical to ensure equitable access to high-quality, biodiverse green spaces for all urban residents. It is important to recognize that the environment encompasses the spaces where people live, work, and recreate [79]. By advancing a more nuanced understanding of urban ecological systems, we can contribute to the design of cities that promote both biodiversity conservation and human well-being.

5. Conclusions

This study clearly demonstrates that in the high-density urban context of Zhengzhou, newly constructed parks designed with biodiversity-friendly principles support significantly higher bird diversity compared to traditional older parks. This enhancement is primarily driven by high-quality habitat features within the parks—particularly diversity of habitat types and complex vegetation structures—coupled with connectivity to other green spaces at the landscape scale. These findings provide an important implication for rapidly urbanizing cities worldwide: through scientifically informed and nuanced ecological design, urban parks can serve as vital refuges for biodiversity conservation. Moving forward, urban green space planning should transition from a focus on expanding area toward improving ecological quality, with priority given to integrating isolated green patches into functional, interconnected ecological networks. Thereby, cities can foster vibrant habitats for birds and other wildlife within increasingly built-up environments.