Fragmented Landscapes as Refuge for Forest Birds in Pakistan and India: A Systematic Review

The average human population in developing countries is increasing rapidly and half of the world population is now living in the cities. The report projections state that the current 7.88 billion population on Earth will increase to 8.5 billion by 2030, 9.7 billion in 2050, and 11.2 billion in 2100 (World Population Prospects, Population Division, United Nations, 2022). The process of human development changes natural landscapes into agricultural and urbanized areas, impermeable ground layers, hydrological process disruptions, exotic vegetation growth followed by a rise in human population, and altered energy and nutrient flows (Menon and Rangaswamy, 2016). Declining biodiversity in cities is mostly associated with habitat alteration, especially vegetation cover and structural changes due to urbanization (Sadam et al., 2021).

The rapid expansion of urban and rural areas has had profound effects on natural ecosystems and biodiversity worldwide, and it has affected the distribution of birds (Archer et al., 2019). Human-dominated areas are highly modified and fragmented habitats that affect the types of birds that occur in cities (Grimm et al., 2008; Aronson et al., 2014; Venter et al., 2016). In many developing countries, some wildlife and birds survive outside protected areas on farmlands, pasture lands, and urban areas (Bolwig et al., 2006). Land transformation poses significant challenges for wildlife, including forest birds (Lampila et al., 2005), as their habitat are increasingly fragmented and transformed, and depending on how these areas are designed and managed, only certain species utilize these areas (Hostetler and Holling, 2000; Zaman et al., 2023).

Forest birds, especially those living in and around the human-dominated areas are among the taxa that are most at risk from land transformation because they depend on good forest habitats for breeding, food, and shelter (Blair, 1996; Kang et al., 2015). Because forest birds have specific ecological niches and environmental needs, they face several challenges as their natural habitats become urbanized (Blair, 1996; Lepczyk et al., 2017). However, human-dominated environments and urban green spaces have the potential to function as essential resources and refuges for some bird species, assisting in their survival (Chace and Walsh, 2006).

Forest birds are important for pollination, seed dissemination, and pest management (Whelan et al., 2008). Their presence in urban and rural areas can promote avian diversity and improve human well-being by adding aesthetic and recreational value (Shochat et al., 2006). Forest birds also act as environmental quality indicators and can promote an understanding of the ecological integrity of cities (Clergeau et al., 2001). We focused on forest birds because most cities have the ability to conserve and plant trees in urban areas. Further, most urban bird surveys are done in parks and residential areas that contain trees (Hostetler and Holling, 2000; Lepczyk et al., 2017). To plan for the conservation of urban forest birds in human-dominated landscapes, conservationists must first understand which forest bird species can be found in cities and agricultural spaces. With such knowledge, it makes it possible to recognize priority species and their unique habitat needs, enabling targeted conservation efforts (Clergeau et al., 2001).

The prime objective of the current study is to determine the forest bird species of India and Pakistan that are potentially adapted to urban environments while maintaining their wilderness ranges because they are somehow vulnerable to rapid changes in the urban environment. The result of this review provides a list of forest birds that could utilize urban environments, helping in the decision-making process for avian conservation.

We carried out a systematic review of peer-reviewed studies of urban forest birds surveyed in urban and rural areas that contained trees and/or small forest fragments. The objective was to create a list of birds that are known to consistently use urban or rural areas that are highly fragmented. The geographic focus was India and Pakistan. These countries share about 3323 km of border length starting from Gujrat/Sindh to Kashmir (Pakistan, 2016). Both countries have been facing issues of uncontrolled urbanization since the start of the 21st century and both of them share the same zoogeographic region i.e. Indomalayan realm and have similar climatic conditions along with many cultural similarities along the borders (Bibi and Métais, 2016). Most of the mountain ranges, plane areas, deserts, and even coastal areas are shared in both of these countries. That is why they share over 70% of flora and fauna (Pakistan- Himalayas, Karakoram, Indus, Britannica, n.d.). We looked for bird studies that were conducted in urban and suburban areas with urban tree canopies and in rural areas that had forest fragments embedded in an agricultural matrix. We considered birds that were either year-round residents or migrants that were using the habitat as a stopover or winter habitat. We focused on these taxa: Accipitridiformes, Anseriformes, Apodiformes, Bucerotiformes, Charadriiformes, Ciconiformes, Columbiformes, Coraciiformes, Cuculiformes, Falconiformes, Gruiformes, Passeriformes, Pelecaniformes, Piciformes, Psittaciformes, Strigiformes, and Suliformes.

An online literature search was performed on articles published from 2000 to 2023 in English. Only original research articles were included in the review and we excluded editorials, comments, and opinion essays. To be included in this review, the research articles had to have reported bird species abundance/presence and were analyzed within urban/rural forest fragments either in the form of urban parks or small forest patches and/or surveys in residential/commercial areas. To identify appropriate articles, we identified a series of keywords and used these as a search string in the Web of Science© online database and Science Direct. We developed our systematic review following the protocol suggested by the Collaboration for Environmental Evidence (CEE, 2013), using the population-intervention-comparator-outcomes (PICO) framework. This framework utilizes a combination of words that maximizes the discovery of relevant articles. This search strategy corresponded to the following: (a) Population – descriptors of those objects of study such as urban forest birds, (b) Interventions - aspects influencing these objects defined such as forest fragment, pocket park, urban trees, (c) Comparator- descriptors of the interventions identified such as fragment size, small fragment, large fragment, and (d) Outcomes- descriptors of outcomes related to objects with identified interventions such as occurrence, abundance, density. Additionally, we also included the words India and Pakistan to define the geographical scope of the review. Likewise, we used the words identified in the previous step to build a search string using Boolean operators like “AND” to link the groups of words between and “OR” to link those words inside of each search. We also used the string the symbol * to find words that have some suffix o prefix commonly used but with a similar meaning (e.g., urban* = urbanization or *urban=suburban). Additionally, we also included in the string the Boolean operator “NOT” linked to broader topics such as climate change and other study topics not considered for this review.

Based on the literature identified in the first step, we developed a list of articles considered suitable for inclusion in the review. We reviewed titles, abstracts, and the full text to determine relevant studies. We screened titles and abstracts of articles discovered through the scientific search engines and rated each as either “0” (not useful) or “1” (potentially useful). For those that received a “1,” we read the full text. We considered articles with forest bird records in urban/rural forest fragments or residential commercial areas with trees in the Indo-Pak subcontinent.

We reported the total number of articles selected for this review and information on the year of publication and country of study. Additionally, from these articles, we constructed a list of all birds that are known to consistently use urban or rural areas that are highly fragmented. Forest birds made the list when they were reported in at least two articles and had a minimum of five individuals seen in a study. For each species, we provided the following: (a) the English common name and scientific name of each selected bird following the taxonomic classification, (b) existing sites associated with the reporting time and dates, (c) the Method used to count the bird population, and (d) the urban/rural green spaces where the forest birds occurred in at least two decades.

We found a total of 127 possible bird studies in India and Pakistan in human-dominated landscapes, but only 10 studies met our criteria where we were able to generate a list of forest birds reported in and around urban habitats like urban green spaces, agricultural lands, and residential/commercial areas (Supplementary Table I). Of these 10 studies, 3 studies included all three habitats, 3 studies included residential areas and agricultural lands, 2 of the studies just reported birds’ density in urban green spaces and residential areas while 1 study just reported urban green spaces, and 1 reported residential areas. Green spaces are areas that have scattered trees in high human areas and some portions covered by small forest fragments. Overall, most studies were published in the last 10 years (80%) with 5 studies in Pakistan and 5 studies in India (Supplementary Table I).

We documented a total of 101 bird species considered to be utilizing trees in human-dominated landscapes. We found 95 bird species (94%) reported in urban green spaces. Out of these 95 species, 65% were primary residents, 23% were winter migrants, 5% were summer breeders, and 7% of the species were considered to be partially resident and winter migrants in the Indo-Pak subcontinent (Table I).

Table I. List of 101 forest bird species in this review identified as users of fragmented landscapes in human dominated areas of India and Pakistan.

1. Altaf et al. (2018); 2. Riaz et al. (2020); 3. Zaman et al. (2023); 4. Sidra et al. (2013); 5. Naithani and Bhatt (2012); 6. Sengupta et al. (2014); 7. Rajpar et al. (2019); 8. Pal et al. (2019); 9. Khera et al. (2009); 10. Tiwary and Urfi (2016).

We found 91 (90%) species in agricultural lands. Out of which 72% of species were primarily year-round residents to the reported areas, 22% were winter migrants and seventy-two species (71%) were reported in residential/commercial areas. Out of these, 9 species were winter migrants, 5 of them were only summer breeders, 5 species were partial resident and winter migrants and the remaining 53 bird species were year-round residents in India and Pakistan (Table I). With a total of 101 bird species identified from 17 orders, Passeriformes exhibited the highest diversity of bird species than the other orders in all three habitats with 47 species in cultivated lands, 45 species in green spaces, and 37 species in residential and commercial areas (Table I). The second largest number of species belonged to Pelecaniformes, and then Accipitridiformes. This diversity emphasizes that human-dominated areas contain possible habitats for a wide array of bird species, including both residents and migratory visitors.

The list of 101 forest bird species spans across several genera. Notably, large species such as shikra (Accipiter badius) and Northern goshawk (Accipiter gentilis) occurred in fragmented areas with trees. Also, migratory species were sighted, such as wood sandpiper (Tringa glareola) and common greenshank (Tringa nebularia); human-dominated areas can provide stopover and wintering habitats along bird migratory flyways (Archer et al., 2019; Xu et al., 2021). However, not all residential landscapes are created equal. Managing the quality and quantity of urban vegetation is key to creating good breeding and stopover habitat within the built environment and native vegetation can increase native bird diversity (Schneider and Miller, 2014). As observed in one of the review studies, greater bird densities and diversities were discovered in residential areas with higher vegetation cover (Sengupta et al., 2014).

Our study results are similar to several review studies of North and South America. In a study of Neotropical migrant birds in South America (Amaya-Espinel and Hostetler, 2019), researchers found that small forest patches and urban tree cover provided some migrants with stopover and wintering habitats. Another study found that certain interior-forest specialists, which are defined as being dependent on extensive forest expanses for successful breeding, utilized small forest fragments in both urban and rural settings and tree canopies within suburban residential areas as crucial stopover sites during migration seasons (Archer et al., 2019). However, some migrating species may primarily forage or take shelter near the centers of forest patches; Dawson and Hostetler (2010) found several migrant species that avoided the edges of forest patches, indicating that the interior of these small urban forest fragments may hold significance for these species. Further, Buron et al. (2022) demonstrated that birds that primarily foraged under the tree canopy typically utilized urban forest patches more than residential treed areas. Additionally, remnant forest patches, located next to developments, are still utilized by migrating and resident bird species (Hostetler et al., 2005). Overall, studies have suggested that both city trees in residential areas and forest fragments in and around cities can provide habitat for different types of forest birds (Archer et al., 2019).

Synanthropic species, or urban dwellers, are birds that can effectively take advantage of human-caused changes and disruptions in an urban environment (Fischer et al., 2015). The presence of forest generalist species in urban environments of India and Pakistan, such as the house crow (Corvus splendens) and common myna (Acridotheres tristis), highlights their adaptability to cities, exploiting food waste generated by humans (Marzluff et al., 2012; Tariq et al., 2024). Other resident species like the house swift (Apus affinis) and Indian ring dove (Streptopelia decaocto) also demonstrate successful adaptation to human-dominated landscapes (Pal et al., 2019). Despite crows being seen in cities, a significant decline in the urban population of house crows has been observed (Radadia, 2013). Factors contributing to this decline could be due to the reduction of trees (Marzluff et al., 2001), crowded and heavily built-up areas (Bernat-Ponce et al., 2018), toxicity in urban environments (Benmazouz et al., 2021; Seress and Liker, 2015), and fluctuations in food availability (Mustafa et al., 2015). This decline in crows since 2011 suggests the vulnerability of synanthropic species in the urban areas of India and Pakistan, underscoring the complex interactions between urbanization and bird ecology.

For forest birds in cities, it is important to conserve forest fragments and trees as cities expand. Developers and city planners must take into account design, construction, and post-construction factors to promote the long-term health of trees and forest patches (Hostetler, 2012). For example, construction practices such as parking heavy machinery in forested areas, failure to protect root zones of trees with proper fencing, and failure to recognize and remove invasive vegetation transported from other areas can greatly reduce the ability of trees to survive and forested areas to retain plant and animal diversity (Hostetler, 2012). Further, nearby residents may impact conserved areas through pollution, exotic animals, and the spreading of invasive plants. Conserving forest patches within an urban area can have limited effects on biodiversity when steps are not taken to ensure its biological integrity. Without long-term management, urban forest patches can become ecological traps-habitats that an organism might favor despite increased livelihood of species mortality and decline (Battin, 2004).

It’s important to note that while this review lists forest birds seen in urban and fragmented rural areas of Pakistan and India, the mere presence of a species does not guarantee thriving populations or long-term persistence. Factors such as disease, competition, pollution, and predation can adversely affect certain species (Wilson et al., 2019). However, these lists serve as a starting point for identifying local species of concern and potential conservation. City planners can then collaborate with ecologists to assess population vitality and conduct further research on breeding success and foraging availability in fragmented and residential areas. While areas with trees could become bird habitats, potential threats to city birds must be carefully addressed through conservation measures and sustainable urban planning (Hostetler, 2012; Wilson et al., 2019).

We extend our sincere gratitude to the Higher Education Commission of Pakistan (HEC) for their generous financial support, which was instrumental in the successful completion of our review article. Our heartfelt thanks go to the Department of Wildlife Ecology and Conservation, IFAS, UF, for their invaluable support. We are also deeply thankful to the dedicated faculty members at Bhauddin Zakariya University Multan’s Department of Forestry and Range Management for their kind cooperation and assistance during the crucial phase of data collection.

The study was partially funded by Higher Education Commission (HEC), Pakistan.

During the preparation of this work, the authors used Chat GPT to enhance the Grammar and readability of the article. After using this service, the authors reviewed and edited the content as needed and took full responsibility for the content of the publication.

There is supplementary material associated with this article. Access the material online at: http://dx.doi.org/10.17582/journal.pjz/..........

The authors have declared no conflict of interest.