The evolution of masturbation in birds

The few studies examining masturbation in non-human animals have used an array of definitions to describe masturbation, and these are often geared towards the study organism. We define masturbation as sexual stimulation of the genitals by self-manipulation. This definition includes individuals using inanimate object(s). Reports of masturbation in birds are most commonly recorded from non-experts using a variety of platforms. As such, we used several approaches to determine how widespread instances of masturbation were documented across avian taxa.<i>Literature review</i>We first performed a literature review to compile published and peer-reviewed accounts of masturbation across avian taxa. We performed electronic searches of the literature in line with the methodology from Mengist, Soromessa and Legese (2019). The search terms used were: “masturbation”, “solo-sex”, “bird”, “mating+behaviour”, “mating+system”. After identifying articles of interest using our search terms, all articles within the final library were read in full and included in the data collection if they met the final criteria and documented or discussed instances of masturbation in avian taxa.<br><i>Avian experts</i>We produced a questionnaire as a tool to survey avian experts in order to quantify how widespread masturbation is across avian taxa. We surveyed experts from academia who either currently or previously conduct research in birds, as well as other professionals and practitioners such as zookeepers. In association with the British and Irish Association of Zoos and Aquariums (BIAZA), this questionnaire was disseminated to all Zoos registered within this organisation. This approach was selected as bird keepers have extensive experience of working in close quarters with their study organisms and could therefore confidently state whether or not they had observed masturbation in their study species. As such, we requested data only for species that the respondent felt they had substantial experience and time observing. Equal attention was paid to respondents who stated that masturbation had never been observed in their study species, however this behaviour was classed as present in species for which a single confirmation of masturbation has been recorded. A species was classed as non-masturbatory if the respondent had never observed this behaviour before and there were no submitted responses to say the contrary.<br><i>Online reports and communities</i>There is a stark disparity between the number of published accounts of masturbation in avian species, in comparison to its widespread documentation from bird keepers, breeders and enthusiasts, particularly within online communities. As such, a vital component of this research was to integrate the extensive knowledge from these individuals and groups with published accounts, to determine how widespread this behaviour is observed across avian taxa. We therefore used a citizen science approach to survey online communities of bird keepers, breeders and enthusiasts for evidence of this behaviour, using the same questionnaire that was sent to avian experts. Further, we extended this methodology to conduct a comprehensive review of documented accounts of masturbation in avian taxa across online communities. We reviewed forums, social media sites (Facebook) and the online video sharing platform, Youtube. For all online data collection accounts, we had set inclusion criteria that posts had to reach in order to be included in the data collection. The minimum requirements were species, sex (either clearly stated or apparent through photographic evidence, such as in sexually dimorphic species), and an accurate written, photographic or video description of the individual(s) masturbating. Any posts that did not reach these minimum requirements were not included in the data collection or any subsequent analysis.A database was created that collated information from all sources regarding this behaviour across avian taxa. We included information detailing species, age (adult/juvenile), sex (male/female), origin (wild/captive), species mating system, social environment and condition (good/bad). For captive species we also recorded the rearing origin which we classed as either parent or hand reared (using human intervention). Social environment was used to record if individuals were housed with others of the same/different sex and the same/different species, and how many were in the group housing situation. Mating system information was gathered from the scientific literature and referenced accordingly.<b>Description:</b> A comprehensive excel spreadsheet with two tabs containing relevant data concerning the presence/absence of masturbation in birds.VariablesOrderSpecies latin and common namesIndication of whether masturbation has been observed in this species beforeIndication of confidence of respondentSex of birdNumber of individuals observed masturbatingWild or captive originGroup sizeHousing conditions with list of four potential optionsRearing origin (hand or parent reared)Age (adult or juvenile)Condition (good or bad)Any applicable notesReliability of data (scored 1-4 with being highest score)There is a second tab on the excel spreadsheet which details the breeding system of birds that were reported in our data.

目前针对非人类动物自淫行为的相关研究寥寥无几，且各研究采用的自淫定义各不相同，往往适配于其所研究的对象物种。本研究将自淫行为定义为通过自主操作对生殖器进行性刺激的行为，该定义涵盖使用无生命物体实施该行为的个体。

目前关于鸟类自淫行为的报道，大多由非专业人士通过各类平台记录。为此，本研究采用多种方法，以明确自淫行为在鸟类类群中的普及程度。

## 文献综述
首先，我们开展文献综述工作，整理已发表且经过同行评议的鸟类类群自淫行为记录。本次文献电子检索遵循Mengist、Soromessa与Legese（2019）的研究方法，检索词设置为："masturbation"、"solo-sex"、"bird"、"mating+behaviour"、"mating+system"。通过检索词筛选出目标文献后，我们通读最终纳入的全部文献，若文献符合最终标准且记录或讨论了鸟类类群的自淫行为，则将其纳入数据集收集范围。

## 鸟类专家调研
我们编制了问卷作为调研工具，走访鸟类领域专家以量化自淫行为在鸟类类群中的普及情况。调研对象涵盖当前或此前从事鸟类研究的学术界专家，以及动物园饲养员等其他相关专业从业者。本问卷与英国及爱尔兰动物园与水族馆协会（British and Irish Association of Zoos and Aquariums, BIAZA）合作，向该组织旗下所有注册动物园发放。选择该发放渠道的原因在于，鸟类饲养员长期与研究对象近距离共处，能够准确判断其是否观察到目标物种的自淫行为。因此，我们仅收集受访者表示拥有充足观察经验与时长的物种相关数据。对于表示未观察到目标物种自淫行为的受访者，我们同样予以同等重视；但若某物种仅存在单例自淫行为确认记录，则将其归类为存在自淫行为的物种。若受访者从未观察到某物种的自淫行为，且无其他受访者提交相反记录，则将该物种归类为无自淫行为的物种。

## 在线报道与社群调研
相较于鸟类饲养者、繁育者与爱好者（尤其是在线社群中）广泛记录的鸟类自淫行为，已发表的相关报道数量相差悬殊。因此，本研究的关键环节之一便是将这些个体与社群的丰富知识与已发表报道相结合，以明确自淫行为在鸟类类群中的观测普及程度。为此，我们采用公民科学（citizen science）方法，使用向鸟类专家发放的同一套问卷，对鸟类饲养者、繁育者与爱好者的在线社群开展调研，以获取该行为的相关证据。此外，我们将该调研方法拓展至对在线社群中鸟类类群自淫行为记录的全面综述工作。我们对论坛、社交媒体平台（Facebook）以及在线视频分享平台YouTube进行了检索审查。针对所有在线数据收集的内容，我们设定了纳入标准，只有符合标准的帖子才能被纳入数据集。最低纳入标准包括：明确的物种信息、性别信息（需清晰标注或通过影像证据佐证，例如性二型物种），以及对发生自淫行为的个体的准确文字、照片或视频描述。未达到上述最低标准的帖子均不会被纳入数据集或后续分析。

我们构建了一个数据库，整合来自所有渠道的鸟类类群自淫行为相关信息。该数据库收录的信息包括：物种名称、年龄（成体/幼体）、性别（雄性/雌性）、个体来源（野生/圈养）、物种交配系统、社会环境以及个体健康状况（良好/不佳）。对于圈养个体，我们还记录其饲养起源，分为亲代抚育饲养与人工干预手养两类。社会环境字段用于记录个体的饲养同伴性别（同性/异性）、物种（同种/异种）以及圈养群体的规模。交配系统相关信息均来自科学文献并标注引用来源。

### 数据集说明
该数据集为一份包含两个工作表的完整Excel表格，涵盖鸟类自淫行为存在/缺失情况的相关数据。
变量包括：
1. 分类阶元（目）
2. 物种学名与通用名
3. 该物种是否曾被观察到自淫行为的标识
4. 受访者的确认置信度
5. 鸟类性别
6. 被观察到发生自淫行为的个体数量
7. 个体来源（野生/圈养）
8. 圈养群体规模
9. 饲养环境（共4种可选选项）
10. 饲养起源（手养或亲代抚育饲养）
11. 年龄（成体或幼体）
12. 健康状况（良好或不佳）
13. 相关备注
14. 数据可靠性评分（评分范围1-4，4分为最高分）

该Excel表格的第二个工作表用于详细说明本数据集收录鸟类物种的繁育系统。