Eggs of Laughing Falcon from nests recorded in 2007 in the Pantanal, state of Mato Grosso do Sul, Brazil, in different nests and months: A (N1) August; B (N3) September; C (N4) October; D (N5) November. 

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... years and reach a diameter at breast height of more than 70 cm (Santos et al. 2006). From the 11 nests monitored, eight nests had one egg or nestling, while only three had two eggs or nestlings, totaling 14 eggs. The eggs were rounded and buff with brown markings, dark brown or purplish brown with darker markings ( Fig. 3), and one egg studied weighed 60 g, measured 56.7 mm in length and 44.3 mm in width, much like what has been observed in others studies (Wolfe 1954, Skutch 1999, Specht et al. 2008). The color patterns of the eggs are slightly different from that reported by other authors, who mention them as being white with a great amount of medium-sized dark brown spots (Wolfe 1954, Specht et al. 2008). The dark purple coloration of some eggs observed is very similar to those of Collared Forest-Falcon ( Micrastur semitorquatus ) as reported in the literature and observed on other occasions at the study site (Barbosa et al. 2014). The clutch size varied from 1–2 eggs/nestlings, as already sug- gested in the literature (Wolfe 1954, Skutch 1999, Ferguson-Lees and Christie 2001), but in 72 % of the nests ( n 5 8) only one egg or nestling was observed, as in some known studies (Skutch 1999, Miller et al. 2010). Many factors have been already mentioned as influencing clutch size in different groups of birds, including latitude and prey availability, among others (Jetz et al. 2008). Based on our data, we can infer that latitude does not appear to influence clutch size in H. cachinnans , but other factors, such as prey availability or type, may have an effect. From the 11 nests recorded, six were found in the breeding season of 2007 and five in 2008. One of the artificial nests (N 2112) found in 2007 was reoccupied by the species in the following year, possibly by the same pair. Among the 11 nests, roughly 45 % ( n 5 5) were depredated while as eggs. The remaining nests consisted of four nests with one nestling each and two nests with two nestlings each. On 7 August 2007, when monitoring nest N3 a couple of Laughing Falcons were observed defending the nest, which upon inspection was empty. Thirty-eight days later, on 14 September, only one adult individual was present and one egg was inside the nest. Thirteen days later, on 27 September, the egg was observed to be intact and an adult individual was present nearby the nest. However, 42 days later on 8 November, the egg was gone and an adult Collared Forest-Falcon had occupied the nest and laid two eggs. In the Pantanal, these species compete with each other for cavities and with other species, such as Hyacinth Macaws (Guedes 2004b, Barbosa et al. 2014). The nestlings observed were very similar in plumage to each other, with the body and wings covered in pale buff plumes, and their distinctive black face masks already evident (Fig. 4A). In one of the nests monitored, a nestling , 1 month old was just a little larger and very similar to the first plumage observed, consisting of pale buff overall, but with brownish wing coverts and dark thin stripes in the head (Fig. 4C). We were not able to check that nest in the following weeks and in the last observations, roughly 1 month later, the young was not in the nest anymore and no adults were seen. We are unable to determine the fate of this nest, though it is plausible the nestling fledged. Four of the eleven clutches were located in nest-boxes. In one of them (N4), we found an egg on 27 October 2007 with the parents close by and vocalizing actively (Fig. 3C). On 3 December, the egg was still there and the parents were present nearby. Ten days later, we recorded a nestling about 3–4 days old, which was photographed and had its vocalization recorded. The calls recorded from this nestling may represent an undescribed vocalization of the species. The calls consisted of short phrases composed of 6–10 notes, lasting 1.5–2 secs, slightly descending in frequency and repeated randomly (Fig. 5). All the single notes varied from 0.5–1 kHz in frequency and 0.1 secs in time, except the first note which is more than two times longer and slightly higher in frequency than the rest. This vocalization is somewhat similar to that emitted by adults when under threat, as they felt on the occasions when we were present nearby their nests. It also consists of short phrases, lasting about 2 sec, composed by roughly 10 notes slightly descending in frequency and with the first note longer and higher in frequency than the remaining (KVCB, pers. obs.). In spite of the similarity between the vocalization of the nestling and the adult and that both are observed when the birds are under some threat, it is still unknown if they are delivered in the same behavioral context. A few other vocalizations have been reported for Laughing Falcon chicks, all of them coming from chicks 2 weeks old or older. Apparent food begging calls, cackle calls during handling and a soft ‘‘wah’’ call were delivered by chicks from 15– 40 days old (Parker et al. 2012). However, there is no mention in the literature of the vocalization type we report here, or from chicks of such an early age (3–4 days old). From the seven natural nests, four were seemingly depredated (N1, N3, N5 and N6), as the eggs disappeared without any sign or remains found. Thus, from the seven nests recorded, only three were successful. The fact that the species breeds only once a year and lays 1–2 eggs each time (White et al. 1994, Specht et al. 2008) and may compete for nest cavities also highlights the importance of the use of nest-boxes in the reproduction of the species. The results presented here reveal new information on the breeding biology of Laughing Falcons, refining the proximal dates of the breeding season of the species in the Pantanal region, providing new descriptions of egg coloration, new information concerning the plumage of the young and a noteworthy, possibly undescribed vocalization of a nestling. From a conservation perspective, this study stresses the importance of monitoring nests of cavity-nesting birds, especially of those experi- encing population declines. Although reports exist of Laughing Falcons using nest-boxes for nesting (Guedes 2004b), this paper provides novel and detailed data on the breeding biology of the species and indicates that Laughing Falcons may successfully reproduce in such nests. Our data also reinforce the importance of large, natural cavities for the reproduction of many bird species and, furthermore, highlight the potential importance of artificial nests, such as nest-boxes, as a conservation tool in situations where there is a genuine shortage of available cavities for ...