Behavioural shift from predominantly indoor to outdoor-resting is becoming widespread in vector populations in settings where anti-vector vector interventions are extensively deployed [6, 15, 16, 35, 36]. The aim of this study was to examine if outdoor resting behaviour of the malaria vector populations described in the study settings [6, 7] was consistent or it was just a random occurrence. The study observed that among the test mosquitoes recaptured, the majority was collected outdoor. This suggested that these mosquitoes returned outdoors to rest after being released indoors. This pattern of preference for outdoor resting in mosquitoes was consistently observed from nine out of the twelve experiments, despite a low recapture rate. As outdoor resting behaviour in vector population could counteract control efforts [18, 37, 38], research assessing the extent of this behaviour is well-timed and necessary to guide decision making in malaria control programmes.
Switch to outdoor-resting behaviour in the vectors may be as a result of avoidance behaviour from indoor interventions [38, 39], which were heavily used in the study sites. Most sleeping rooms had LLINs and they were also sprayed with pirimiphos methyl, the insecticide that was being used for IRS at the time of the experiments . These mosquitoes might be avoiding contact with the insecticide indoors and chose to rest outdoors, where they may be safe, as there was no outdoor intervention in the villages. This could have also accounted for the predominant outdoor resting preference documented in the vectors in a previous study from this setting  and others all over Africa [6, 8, 12, 36, 37], which prompted this investigation.
The highly endophilic vectors: An. gambiae s.s., An. coluzzii and An. funestus s.s. were recaptured outdoors after being released indoors. This suggests a likely switch to outdoor resting behavior because these vector species may be avoiding contact with insecticide indoors and exiting to rest outdoors [40–42]. Change from endophily to exophily in response to control intervention is increasingly being documented in these highly endophilic vectors [8, 12, 16, 35, 43, 44]. This could have negative impact on malaria control as it can promote outdoor and residual transmission in these settings [11, 38, 45].
Anopheles arabiensis was found to predominate the mosquito species found resting outdoors from the recaptured test mosquitoes. This may be because An. arabiensis is known to be highly exophilic and zoophilic (preference for animal blood meal) [46–48], where it tends to stays outdoors to rest and feed on animals when there is intervention indoors [4, 49]. This vector species has also been observed to display insecticide avoidance and early-exiting behaviour [12, 18, 42], which make them difficult to control 
In this study, the recapture rate was much lower than most MRR studies reported. Several reasons could have accounted for this. One of such reasons is that the intervention indoors could have could have killed the mosquitoes while attempting to rest post-feeding [50, 51]. Another reason is the age of mosquitoes [20, 22, 52], which was unknown in this study. Plausibly, if the mosquitoes were old, they may have died within the period of recapture. Indeed, senescence is a factor associated with reduction of mosquito daily survival in the wild [53, 54]. Age was also previously suggested to be responsible for the low recapture rate in a similar experiment . Moreover, predators such as spiders were particularly common in the study areas, and were found inside animal houses that provide favourable environment for the mosquitoes to rest. Likewise, as some of the released mosquitoes were blood fed as well as semi-gravid and gravid, they might divert to seeking favorable oviposition spots which naturally occurs in the night. These mosquitoes may not return to rest within the same locality or might have been exposed to predators or died naturally. Other factors including emigration from the study area, climate condition, stress and negative effect of the experimental procedures could have also contributed to this low recapture success as previously documented in other MRR experiments [20, 22, 27].
The study also recaptured more mosquitoes during the rainy season relative to the dry season. This might be because more mosquitoes were released during this rainy season as expected. However, none of the control mosquitoes was recaptured throughout the experiments. The possible explanations could be that the mosquitoes might have died due to the residual effect of insecticides [50, 51] from their initial contact before collection. It may also be due to predators attack and other factors as suggested above.