Crocodilian Species Research Articles

Crocodiles of the Ouémé lower valley in Southern Benin: Local perceptions, uses and conservation challenges

The Ouémé Lower Valley, located in Southern Benin, is renowned for its rich biodiversity, which includes three species of crocodiles. Despite the presence of the crocodile species, the relation between these species and the local population is not well known. In this study, we aimed to examine local perceptions of crocodiles, document their uses, and identify conservation challenges. Over a period of 10 months, we surveyed the local population to understand their perceptions of crocodiles and the uses they make of these animals. Given the critical role of perceived threats in shaping conservation attitudes and behaviours, our objective also included analyzing perceived threats to crocodiles. From the 420 individuals interviewed, 90 % have a negative perception of crocodiles, perceiving them as harmful. However, 10 % of respondents, mainly from the 'Xwla' ethnic group, have a positive perception, perceiving crocodiles as harmless and beneficial. Local communities attribute various virtues to crocodile by-products, with crocodile teeth being the most cited, valued for their protective qualities. According to them, the decline in crocodile populations in the area is attributed primarily to poaching, agriculture, and sand extraction, as reported by 35 %, 28 %, and 22 % of respondents, respectively. Educational initiatives aimed at raising awareness about the ecological significance of crocodiles should be implemented, particularly targeting ethnic groups with negative perceptions of crocodiles in the region. Future researches are also needed in order to study in deep the impacts of anthropic activities on the crocodile population in the area.

Host species and age‐specific variation on Hepatozoon prevalence and its effect on body condition in two Neotropical crocodiles

Many populations of species belonging to the order Crocodilia are threatened due to illegal trafficking, indiscriminate hunting, and habitat loss and degradation affecting crocodilian health and parasitic load. Although several studies have revealed that crocodiles, caimans, and alligators are frequently infected by Hepatozoon spp., the results from studies exploring the costs of these apicomplexan parasites on the health of their reptilian hosts are still scarce and with inconclusive results. Here, we molecularly assessed the prevalence and genetic diversity of Hepatozoon spp. to explore their possible influence on body condition in captive individuals of two species of Neotropical crocodilians with conservation threats, the spectacled caiman Caiman crocodilus and the American crocodile Crocodylus acutus. Fourteen percent of spectacled caimans were infected by H. caimani, whereas no American crocodiles showed infection. The prevalence of Hepatozoon in spectacled alligators varied along age, where subadult individuals were the most frequently parasitized. Surprisingly, the body condition of infected individuals was significantly higher than body condition of uninfected spectacled caimans, which suggests greater negative effects of the infection in individuals of poor quality. Also, the body condition of subadult individuals was significantly higher than body condition of juveniles of both alligator species, likely reflecting differences in the occupancy of habitats with higher resource abundance, or variations in the nutritional values of the diet between these age classes. These outcomes provide valuable information on disease ecology for developing conservation strategies and the management conservation of wildlife populations of these species.

Prevalence of injuries in a Caiman crocodilus chiapasius (Bocourt 1876) population from the South Pacific coast of Mexico

ABSTRACT Crocodilians injuries are indicators of their health and social interactions. We analyzed the prevalence and distribution of injuries in spectacled caiman (Caiman crocodilus chiapasius) from the Biosphere Reserve of La Encrucijada (BRLE) in relation to the habitat, size, and sex of individuals. We collected data on injuries in caimans captured during nocturnal surveys (2014–2022) in the estuary and swamps of the BRLE. We determined the sex of each caiman, measured their snout–vent length, and registered the type of injury and body region where injuries were detected. From all records, 102 of 301 caimans (33.9%) presented injuries and they were more likely to be injured in the estuary than in the swamps, probably due to the presence of a larger sympatric crocodile species in the estuary (Crocodylus acutus). Sex had no effect on the proportion of injured individuals, but larger caimans have a higher probability of being injured than smaller ones, explained by an ontogenetic change in the individuals’ behaviors. Habitat, sex, and size class of individuals do not influence the number of injuries on different body regions. The tail was the most injured body region (17.6% of individuals), followed by the abdomen (13.0%), back (12.6%), head (9.6%), and extremities (4.0%).

Congenital Anomalies in American Crocodile (Crocodylus acutus, Cuvier, 1807) Embryos from a Farm Breeder in Colombia.

The American crocodile (Crocodylus acutus, Cuvier, 1807) (Class Reptilia, Family Crocodylidae) is a crocodile species inhabiting the Neotropics. Congenital defects have been described in almost every vertebrate group. In crocodiles, teratology alterations have been described in captive animals (pets, zoos, farms) such as Crocodylus niloticus or Gavialis gangeticus. The present study aimed to characterize congenital malformations of C. acutus from a farm in Lomas de Matunilla, Ballestas, Bolívar, Colombia. A total of 550 unhatched eggs were examined after embryo death. A total of 61 embryos presented malformations, with 42 different types of anomalies observed. Limb and tail malformations (29%) were the most common malformations observed. Several malformations, such as cephalothoracopagus, thoracopagus, sternopagus, xiphopagus twins, campylorrachis scoliosa, and acrania, were documented in crocodiles for the first time. Research in teratology enhances our understanding of crocodile biology. It plays a role in their conservation and management, thus helping to ensure the long-term viability of these species in their natural habitats.

Temperature-Dependent Sex Determination in Crocodilians and Climate Challenges.

The sex of crocodilians is determined by the temperature to which the eggs, and hence the developing embryo are exposed during critical periods of development. Temperature-dependent sex determination is a process that occurs in all crocodilians and numerous other reptile taxa. The study of artificial incubation temperatures in different species of crocodiles and alligators has determined the specific temperature ranges that result in altered sex ratios. It has also revealed the precise temperature thresholds at which an equal number of males and females are generated, as well as the specific developmental period during which the sex of the hatchlings may be shifted. This review will examine the molecular basis of the sex-determination mechanism in crocodilians elucidated during recent decades. It will focus on the many patterns and theories associated with this process. Additionally, we will examine the consequences that arise after hatching due to changes in incubation temperatures, as well as the potential benefits and dangers of a changing climate for crocodilians who display sex determination based on temperature.

Preliminary assessment of blood mercury contamination in four African crocodile species

Heavy metal contamination in the environment is an increasingly pervasive threat to the long-term persistence of wildlife. As high trophic level consumers, crocodylians are at substantial risk from bioaccumulation of mercury (Hg). Despite that they are generally well-studied and the focal species of many conservation efforts around the world, little is known about Hg contamination levels in most crocodylians. Here we preliminarily evaluate blood Hg contamination in four African species – Central African slender-snouted crocodile (Mecistops leptorhynchus), African dwarf crocodile (Osteolaemus tetraspis), West African crocodile (Crocodylus suchus), and Nile crocodile (Crocodylus niloticus) – from a diversity of sites and habitats across 5 different countries representing varying degrees of environmental pollution. All of our sampled crocodiles were Hg contaminated and, worryingly, these African crocodiles generally showed the highest levels of Hg contamination of any crocodylian species examined to date. Of most concern was that Hg concentrations were not only highest in M. leptorhynchus, the most threatened amongst our study species, but also in individuals sampled in what are believed to be some of the most remote and pristine natural areas left in Africa – Gabon’s national parks. Our results underscore the need to better understand the impact of longstanding petroleum, mining, forestry, and agricultural industries on the entire aquatic food chain throughout much of Africa, including on the threatened species in these habitats and the human populations that depend on them for their subsistence and livelihoods.

Nuclei and Tracts in the Telencephalon of Crocodiles: Identification and Characterization Using an Organizational Scheme Applicable to Other Reptiles.

The telencephalon of reptiles has been suggested to be the key to understanding the evolution of the forebrain. Nevertheless, a meaningful framework to organize the telencephalon in any reptile has, with rare exception, yet to be presented. To address this gap in knowledge, the telencephalon was investigated in two species of crocodiles. A variety of morphological stains were used to examine tissue in transverse, horizontal, and sagittal planes of sections. Besides providing a description of individual nuclei, brain parts were organized based on two features. One was related to two fixed, internal structures: the lateral ventricle and the dorsal medullary lamina. The other was the alignment of neurons into either layers, cortex, or not, nucleus. Viewed from this perspective, all structures, with limited exceptions, could be accurately placed within the telencephalon regardless of the plane of section. Furthermore, this framework can be applied to other reptiles. A further extension of this scheme suggests that all structures in the telencephalon could be grouped into one of two categories: pallial or basal.

Crocodilian Phallic Malformations and Anomalies

Abstract Phallic malformations directly impact crocodilian copulatory function and thus could impact reproductive success in individual animals. This case series characterizes malformations observed and the implied reproductive consequences. We assessed a range of phallic malformations observed in saltwater crocodile (Crocodylus porosus), Nile crocodile (Crocodylus niloticus), broad-snouted caiman (Caiman latirostris), and Cuban crocodile (Crocodylus rhombifer) during veterinary examinations or postmortem studies and characterized observation into the following categories: amputation, phallic glans malformations, sulcus spermaticus obstruction, and prolapse. Through detailed descriptions of these anomalies, we discuss potential reproductive health impact based on current knowledge across crocodilian species. When considering captive management of breeding stock, it is vital to examine individual efficacy at achieving proper intromission and insemination. Therefore, full reproductive examination in males should be part of routine examination to best manage individuals with such anomalies.

Pharmacokinetics of tildipirosin in estuarine (Crocodylus porosus) and freshwater (Crocodylus siamensis) crocodiles

Tildipirosin is a macrolide antimicrobial. It is authorised for the treatment and prevention of respiratory disease in cattle and pigs. There are no data on its administration in crocodiles. Therefore, this study evaluated the disposition kinetics of tildipirosin after intravenous (dose: 2 mg/kg) and intramuscular (doses: 2 and 4 mg/kg) administration in two crocodilian species (estuarine and freshwater; n = 5). Tildipirosin plasma concentrations were quantified by a validated HPLC method. Plasma concentrations obtained at each extraction time were analysed by non-compartmental methods. In the estuarine and freshwater crocodiles, the apparent volumes of distribution of tildipirosin after intravenous administration were 0.36 ± 0.10 and 1.48 ± 0.26 L/kg, respectively. These values, suggesting poorer tissue distribution, were much lower than those obtained in mammals. There was complete bioavailability of tildipirosin after intramuscular route at a dose of 2 mg/kg; however, at a dose of 4 mg/kg the bioavailability decreased by about 20–25 %. Furthermore, the pharmacokinetics of tildipirosin were markedly different in the two crocodilian species. Considering a MIC of 0.5 µg/mL, the surrogate marker AUC0–24/MIC indicates that tildipirosin would greatly exceed the value of 65 h for both crocodile species and dose levels tested. This suggests that both doses (2 and 4 mg/kg) may provide a bactericidal effect. Therefore, based on the absence of adverse reactions following the administration of tildipirosin in both crocodilian species, and considering its favourable pharmacokinetic properties, tildipirosin may be useful in treating infections in these reptiles.

Increasing Population Status of Broad-Snouted Caiman (Caiman latirostris) Based on Sustainable Use Strategies in a Managed Protected Area in Santa Fe, Argentina.

People and crocodilians have engaged in interactions since the earliest human settlements. After many years of escalating non-regulated use, coupled with emerging threats such as habitat modification, environmental pollution, and the exponential growth of human populations, natural crocodilian populations have been pushed to the brink of extinction. To prevent this, various initiatives have implemented strategies to prevent local extinction. Reinforcing wild populations through reintroductions and head-starting programs has been considered the safest approach to recovering crocodilian populations. Subsequently, the concept of sustainability emerged. In the case of many historically exploited crocodilian species, it became evident that rational utilization need not adversely affect population status; on the contrary, there were clear signs of recovery when local communities were involved. In 1990, the broad-snouted caiman (Caiman latirostris) was in a critical state due to decades of poaching and the aforementioned threats. In response, the "Monitoring and restocking program of the broad-snouted caiman for management purposes", commonly known as Proyecto Yacaré, was established to study population abundance and assess the biological, ecological, and social response to this management methodology. As a result of the eggs's harvest, a proportion equivalent to or greater than what would have survived in natural conditions was released into the original habitat where the eggs were collected. The surplus was allocated for leather and meat production with a focus on economic and environmentally sustainable practices, without affecting biodiversity or threats to the managed species. The in situ work carried out by this program has been crucial for the recovery of broad-snouted caiman populations under the "incentives for conservation" system, whereby local communities receive benefits for nest identification and egg harvesting. Over time, conservation incentives have become significant contributors to regional economies. This study illustrates how C. latirostris populations increased due to the implementation of egg harvesting by local communities in a natural reserve for management purposes. This population increase was detected through continuous night monitoring and an analysis of the number of nests in the area. Currently, C. latirostris populations have transitioned from being among the most threatened to becoming one of the most abundant throughout their distribution area. Based on the analyzed information, we may affirm that the commercial value of these species is one of the most relevant aspects contributing to the sustainability of these programs, primarily due to the change in perception generated among local communities. Therefore, identifying and controlling factors affecting these programs are fundamental for the conservation of these species.

Population status and genetic assessment of mugger (Crocodylus palustris) in a tropical regulated river system in North India

For rewilding the depleted crocodylian populations in India, a targeted ‘one-species one area’ based conservation approach was adopted in the early-1970s. Suitable habitats were identified and designated as protected areas, specifically targeted to recover a particular crocodylian species. A ~ 610 km stretch of Chambal River in the Ganga River Basin was declared as National Chambal Sanctuary to restore the ‘Critically Endangered’ gharial (Gavialis gangeticus), where active management of mugger (Crocodylus palustris) was discouraged. In the present study, we examined the population trends, occupancy, and genetic status of mugger by conducting population monitoring and genetic assessment to understand the status of potentially competitive mugger in the Sanctuary. Our finding suggests that the mugger population has notably increased and colonised the Sanctuary. We observed a moderate level of genetic diversity in the mugger, which was relatively higher compared to the gharial in the Sanctuary. The rapid colonization of ecological generalist mugger raises concerns about potential competition with ecological specialist gharial threatening its long-term sustainability. Considering the coexistence dynamics between the species, it is essential to extend adaptive management strategies for mugger to ensure successful recovery of gharial population in the Sanctuary.

Osteology of Crocodylus palaeindicus from the late Miocene–Pleistocene of South Asia and the phylogenetic relationships of crocodyloids

Fossil crocodylian remains have been documented from India and other parts of South Asia since the mid-nineteenth century, but specimens attributed to several extinct and extant species of Crocodylus have largely been neglected in modern taxonomic treatments. Here, we present a detailed anatomical description of the extinct species Crocodylus palaeindicus, which we restrict to the late Miocene to early middle Pleistocene of India. Using an autapomorphy-based approach to species-level identification, we regard Crocodylus sivalensis as a junior synonym of C. palaeindicus and provide taxonomic re-identifications of all specimens previously referred to these two species. We present a new diagnosis for C. palaeindicus that facilitates its distinction from the extant mugger crocodile, C. palustris, which does not unequivocally appear in the fossil record prior to the Pleistocene. The lack of clear spatiotemporal overlap, coupled with the otherwise lengthy ghost lineage implied by their sister-taxon relationship in our phylogenetic analyses, provides tentative support that the extant species either is the descendant of C. palaeindicus or originated via budding cladogenesis. An expanded phylogenetic analysis recovers the late Miocene African C. checchiai and Pliocene South American C. falconensis as species within the Neotropical Crocodylus clade, supporting an African origin for this radiation. We also recover Kinyang, from the early–middle Miocene of Kenya, as a crocodyline, rather than an osteolaemine as originally described, and it is potentially the stratigraphically earliest known member of the Crocodylus lineage. Other notable results from our phylogenetic analyses suggest that crocodyloids might not have been present in North America prior to the late Neogene arrival of Crocodylus, with Albertosuchus knudsenii, Prodiplocynodon langi and ‘Crocodylus’ affinis all recovered outside of Crocodyloidea. Furthermore, we demonstrate that an alligatoroid placement for the recently erected latest Cretaceous–Palaeogene East Asian clade Orientalosuchina is highly labile, with relationships at the ‘base’ of Crocodylia unstable.

Estimating Total Length of Partially Submerged Crocodylians from Drone Imagery

Understanding the demographic structure is vital for wildlife research and conservation. For crocodylians, accurately estimating total length and demographic class usually necessitates close observation or capture, often of partially immersed individuals, leading to potential imprecision and risk. Drone technology offers a bias-free, safer alternative for classification. We evaluated the effectiveness of drone photos combined with head length allometric relationships to estimate total length, and propose a standardized method for drone-based crocodylian demographic classification. We evaluated error sources related to drone flight parameters using standardized targets. An allometric framework correlating head to total length for 17 crocodylian species was developed, incorporating confidence intervals to account for imprecision sources (e.g., allometric accuracy, head inclination, observer bias, terrain variability). This method was applied to wild crocodylians through drone photography. Target measurements from drone imagery, across various resolutions and sizes, were consistent with their actual dimensions. Terrain effects were less impactful than Ground-Sample Distance (GSD) errors from photogrammetric software. The allometric framework predicted lengths within ≃11–18% accuracy across species, with natural allometric variation among individuals explaining much of this range. Compared to traditional methods that can be subjective and risky, our drone-based approach is objective, efficient, fast, cheap, non-invasive, and safe. Nonetheless, further refinements are needed to extend survey times and better include smaller size classes.

Community engagement and human perception in crocodile conservation: preliminary steps in Sian Ka’an Biosphere Reserve

IntroductionWildlife tourism is important for the conservation of protected areas, endangered species, and to empower local communities. Nevertheless, when guidelines and practices are not clear and correctly executed, tourism may have a negative impact.MethodsWe carried out semi-open interviews (n = 34) and several workshops (n = 50) with locals and tour guides in the village of Punta Allen in Sian Ka'an Biosphere Reserve, Mexico. Data were organized in tables in Excel®, and statistical analysis was conducted with IBM® SPSS® Statistics software. A priori, exploratory data analysis was carried out to identify the general pattern of the data, and a priori data normality test (Shapiro–Wilks) and χ2 test were carried out to find out if there were differences in the frequency of a response depending on socioeconomic variables.ResultsMost respondents (69%) dedicated 2–10 min to crocodile observation, one quarter (25%) spent 11–20 min, and the remainder (6%) 21–30 min. The majority (97%) of respondents mentioned that when they see a crocodile, they approach at a 5–10 m distance and wait for the occupants of the boat to take pictures, and then leave; only one respondent (3%) said that they feed crocodiles to attract them to the boat. Most respondents (89%) said that crocodile observation does not need to be improved, and it is fine the way it is currently carried out; the remaining 11% said that it could be improved. Workshops were received positively and allowed us to share information on crocodile species, their conservation, and good tourism practices.DiscussionIt is necessary to enlighten tourism service providers about the biology and importance of crocodilian species, to promote conservation and provide services with an educational impact/focus for visitors to the reserve. There is a need to develop a communication program that provides accurate information for new service providers and renews and reinforces concepts for established providers. Additionally, we need to continuously monitor and evaluate wildlife observation activities to enhance current practices in our study area, and to determine if they are having a negative impact on crocodile behavior and biology.

Experimental and numerical investigation on novel three-dimensional printed bio-inspired hexagonal lattices for energy absorption and stiffness behavior

In the current study, a new type of novel lattice structures with the concept of bio-mimicking three different nature-inspired designs from the honeycomb patterns, the overlapping phenomenon of the scales present on fish dermal layers, and scutes pattern observed from the top skin layers present on crocodile species are developed. These lattice structures are designed within a cubic volume of 30 mm. The design of lattice unit cells is made with two different geometrical sizes of 4 and 6 mm with different overlapping areas of 20, 30, 40, and 50% calculated from each cell area. All the unit cells’ walls are maintained at 0.4 and 0.6 mm only. The specimens are modeled and manufactured through the VAT photopolymerization process, one of the significant additive manufacturing principles for great dimensional accuracy with negligible defects in 3D printing (3DP). The research approach used to develop lightweight bio-inspired structures has been laid out, starting with observing design that served as inspiration. The cured 3D-printed specimens are examined under quasi-static compressive loading carried out on all specimens as per ASTM 1621 standards to measure the crashworthiness response of designed specimens. The energy ingestion capacity of all the specimens is assessed. A good correlation is observed between the experimental and numerical results for better validation. The best design parameters among all 16 specimens are identified for applying energy absorption applications in the automobile and aviation fields in real-time.

Blood Biochemical Reference Intervals of Black Caimans (Melanosuchus niger) and Spectacled Caimans (Caiman crocodilus) in the Brazilian Amazon Region.

Reference intervals for physiologic parameters, crucial for assessing the health status of animals, have been documented for various crocodilian species across the globe. Nonetheless, the establishment of plasma biochemical reference intervals specific to Amazonian crocodilians remains incomplete. In an effort to address this gap, we procured blood samples from 65 black caimans (Melanosuchus niger) and 58 spectacled caimans (Caiman crocodilus) during the period of September-December 2019 within the Anavilhanas National Park in the Brazilian Amazon region We aimed to define reference intervals for 11 key plasma variables measured, namely glucose, triglycerides, total cholesterol, calcium, magnesium, sodium, potassium, albumin, total protein, uric acid, and urea. In general, the determined blood reference intervals aligned closely with those established for other crocodilian species. Some specific measurements, such as total cholesterol, sodium, and magnesium, exhibited distinct variations based on the species. Furthermore, female black caimans showcased elevated cholesterol levels compared with their male counterparts. Within the spectacled caimans, disparities related to sex were evident solely in the case of electrolytes sodium and potassium, with males demonstrating higher levels compared with females. These reference intervals not only provide data for assessing potential fluctuations in the health of wild or captive Amazonian crocodilians but also hold value for veterinary management.

Cytochrome oxidase I DNA barcodes of crocodilians meat selling in Hong Kong

The crocodilians include true crocodiles, alligators, caimans, and gharial, and the trade of crocodilian products is regulated in accordance with the Convention of Wild Fauna and Flora (CITES). Hong Kong does not have her own wild crocodilians; thus, all crocodilians meat available is presumably imported with proper license. Here, we obtained a dataset of cytochrome oxidase I (COI) gene markers of 114 crocodilian meat samples (including frozen and dried crocodilian meat products) available in the contemporary market. We have also validated these barcodes in a phylogenetic approach with other data deposited on the GenBank, and detected 112 samples belonging to four crocodile species Crocodylus siamensis, C. porosus, C. niloticus and Alligator mississippiensis, and 2 samples belonging to snake Malayopython reticulatus. The dataset generated in this study will be useful for further studies including meat inspection, illegal trading, and enhancement of international and local legislations on illegal reptile importation.

Primeiro relato de predação de um jacaré-coroa (Paleosuchus trigonatus) por uma lontra (Lontra longicaudis)

ABSTRACT Lontra longicaudis is a semi-aquatic predator which mainly feeds on fish and crustaceans, but which can opportunistically predate mammals, birds, and reptiles. In the Amazon, this species is sympatric with Paleosuchus trigonatus, one of the smallest species of crocodilians, whose possible means of defense is a very rigid skin, which causes adults to have few predators. Here we report the first documented case of predation of P. trigonatus by L. longicaudis.

Hindlimb and pelvic anatomy of Caiman yacare (Archosauria, Pseudosuchia): Myology and osteological correlates with emphasis on lower leg and autopodial musculature.

The anatomy of the archosaurian pelvis and hindlimb has adopted a diversity of successful configurations allowing a wide range of postures during the evolution of the group (e.g., erect, sprawling). For this reason, thorough studies of the structure and function of the pelvic and hindlimb musculature of crocodylians are required and provide the possibility to expand their implications for the evolution of archosaurian locomotion, as well as to identify potential new characters based on muscles and their bony correlates. In this study, we give a detailed description of the pelvic and hindlimb musculature of the South American alligator Caiman yacare, providing comprehensive novel information regarding lower limb and autopodial muscles. Particularly for the pedal muscles, we propose a new classification for the dorsal and ventral muscles of the autopodium based on the organisation of these muscles in successive layers. We have studied the myology in a global background in which we have compared the Caiman yacare musculature with other crocodylians. In this sense, differences in the arrangement of m. flexor tibialis internus 1, m. flexor tibialis externus, m. iliofibularis, mm. puboischiofemorales internii 1 and 2, between Ca. yacare and other crocodylians were found. We also discuss the muscle attachments that have different bony correlates among the crocodylian species and their morphological variation. Most of the correlates did not exhibit great variation among the species compared. The majority of the recognised correlates were identified in the pelvic girdle; additionally, some bony correlates associated with the pedal muscles are highlighted here for the first time. This research provides a wide framework for future studies on comparative anatomy and functional morphology, which could contribute to improving the character definition used in phylogenetic analyses and to understand the patterns of musculoskeletal hindlimb evolution.

The Various Ways in Which Birds Blink

There has, to date, been no systematic study of the various ways in which birds blink. Digital video recordings were made, and studied using still frames, of 524 bird species, mainly in zoos but also in the wild. Videos on 106 species from various sites on the internet were studied, some of which we had also videoed, giving a total of 591 (out of a possible 10,000) species from all 43 orders and 125 (out of a possible 249) families. Digital video recordings were also made of 15 (out of a possible 24) species of crocodile. Three types of blink were observed in birds: (1) Nictitating membrane blinks were rapid and brief (phasic) and occurred mainly on head movement. (2) Upper lid blinks were seen in parrots, owls, pigeons and some others. These were also rapid and brief and accompanied nictitating membrane blinks. (3) Lower lid blinks were slow and sustained (tonic) and occurred with drowsiness and preening. Nictitating membrane blinks and lower lid blinks were seen in crocodiles but not upper lid blinks. Globe retraction, where the eyeball is pulled into the orbit of the skull during a blink, was seen in crocodiles but not birds. Phasic blinks remove debris and moisten the cornea, essential for allowing oxygen to diffuse into the cornea, which has no blood supply. Tonic blinks are probably mainly protective. The orders of birds which have upper lid blinking are not closely related and this feature is probably the result of convergent evolution.