The effect of hunger on the acoustic individuality in begging calls of a colonially breeding weaver bird

Abstract

BackgroundIn colonially breeding birds, the ability to discriminate between individuals is often essential. During post-fledging care, parents have to recognize their own offspring among many other unrelated chicks in the breeding colony. It is well known that fledglings and food-provisioning parents of many bird species use contact calls to convey their identity. These calls are also often used as hunger-related signals of need in young birds. Here, we investigate how such calls incorporate signals of need and at the same time act as reliable indicators of each chick's identity.ResultsIn a field study, we experimentally manipulated the hunger level of colonially breeding Jackson's golden-backed weaver (Ploceus jacksoni) nestlings close to fledging and investigated its effects on acoustic call parameters. Some acoustic parameters that were related to the time-frequency pattern showed high individuality and were largely unaffected by a nestling's state of hunger. However, the majority of call parameters were significantly affected by hunger. Interestingly, most of these acoustic parameters showed both consistent changes with hunger and high between-individual differences, i.e. potential for individual recognition.ConclusionThe results indicate that individual recognition processes can be based on static, hunger-independent call parameters, but also on dynamic hunger-related parameters that show high individuality. Furthermore, these signal properties suggest that the assessment of signals of need can be improved if the signal value is referenced to a chick's vocal spectrum.

Individual vocal signatures in barn owl nestlings: does individual recognition have an adaptive role in sibling vocal competition?

“…Nestling individual discrimination was significantly higher in a food‐deprived than food‐satiated state (36% of success vs. 31%). This is consistent with a previous study in Jackson's golden‐backed weavers ( Ploceus jacksoni ) showing that chicks were more easily identifiable statistically when begging in a hungry than in satiated state (Reers & Jacot, ). Using the same argumentation as above, this finding is not surprising.…”

“…Because the next prey item is highly valuable for hungry nestlings and they invest more effort in calling than food‐satiated nestlings, they would derive more benefits from being identified as motivated competitors to be given the priority to the prey. Alternatively, the change in discriminability with hunger level could be a nonadaptive by‐product, due to the fact that nestlings’ motivation is more variable when food‐satiated, and they signal at maximal and stable level when food‐deprived (Reers & Jacot, ). This argument does not apply to the barn owl, as we showed that the acoustic features signalling hunger level (such as call duration) present similar within‐individual repeatability when food‐deprived and food‐satiated.…”

“…In family interactions, offspring vocal signatures allow nestmates to modify competitive behaviour according to kinship (Boncoraglio et al, 2009) and parents to recognize their progeny and avoid feeding alien offspring (Holley, 1984;Aubin & Jouventin, 1998;Levrero et al, 2009). Because animal vocalization can not only reveal their identity but also signal motivation to compete and resource-holding potential, different vocal cues may be used to perform these multiple tasks (Reers & Jacot, 2011). For instance, offspring begging calls can simultaneously advertise need for parental care (Christe et al, 1996;Marques et al, 2009) and identity (Levrero et al, 2009).…”

Innate development of acoustic signals for host parent–offspring recognition in the brood‐parasitic Screaming CowbirdMolothrus rufoaxillaris

“…In Mockingbird nests, Screaming Cowbird nestlings are rapidly outgrown by their larger host nest-mates and are thus expected to be hungrier than in Baywing nests and to compete more strongly to secure sufficient provisioning (De M arsico & Reboreda 2008). In other passerine species, deprived nestlings increase call duration, bandwidth or frequency modulation as their hunger level increases (Leonard & Horn 2006, Marques et al 2008, Reers & Jacot 2011, but see Anderson et al 2010). These observations accord with prior experimental work showing that Screaming Cowbird nestlings deprived of food increase the intensity of their begging displays as deprivation time increases (Lichtenstein 2001) and are more consistent with begging effort by Screaming Cowbirds as a signal of hunger rather than need (Mock et al 2011).…”

Parent–environmental interactions shape acoustic signatures in tree swallows: a cross‐fostering experiment

“…We used Sound Analysis Pro (SAP) (for details see Tchernichovski et al 2000, Tchernichovski and Mitra 2004) to measure the following nine call features (see Table 1 for descriptions) of the first 25 calls on each recording that were free of background noise (total of 610 calls from 60 nestlings, mean ± SD 10.2 ± 5.8 calls/nestling, range: 1–25 calls/nestling): 1) duration of call part (in ms); 2) variance of amplitude modulation (in ms −1 ); 3) mean frequency (in Hz); 4) mean frequency modulation (°); 5) variance of frequency modulation (°); 6) mean entropy; 7) variance in entropy; 8) mean pitch (in Hz) and 9) mean pitch goodness. These features have been previously shown to be important in acoustic signatures, showing considerable variation across songbird nestlings (Jacot et al 2010, Reers and Jacot 2011, Reers et al 2011).…”